JP7773966B2 - Switching power supply device and power supply system using the same - Google Patents

Description

The present invention relates to a switching power supply device with a remote sensing function and a power supply system using the same.

When the load line connecting the switching power supply to the load becomes long, the voltage drop across the load line increases when output current flows through it, causing the load end voltage to deviate from the target voltage. To address this issue, remote sensing has traditionally been used to obtain information on the load end voltage, and the operation of the switching power supply is controlled based on this information.

For example, Patent Document 1 describes a switching power supply that directly detects the load end voltage via a sensing line, inputs the detected value to an error amplifier, and performs feedback control of the load end voltage.

Patent document 2 also describes a power supply device that detects the output terminal voltage V2 and output current I, and indirectly recognizes the load line voltage drop I・r by multiplying the detected value of I by a pre-registered load line resistance value r, and adjusts the output terminal voltage target value V2m so that the relationship V1m = V2m + I・r (V1m is the target value of the load terminal voltage V1) holds.

Japanese Patent Application Publication No. 7-241074 Japanese Patent Application Publication No. 9-34561

The switching power supply in Patent Document 1 has a long sensing wire in the feedback control system for stabilizing the load end voltage. As a result, the inductance component of the sensing wire makes the feedback control system more susceptible to oscillation, and the longer the sensing wire, the more difficult it becomes to design the control system.

The power supply device in Patent Document 2 detects voltage drops in the load line and performs feedforward control. Because no sensing wires are involved in the feedback control system (sensing wires themselves are not required), the problem of feedback control systems being prone to oscillation can be avoided. However, every time the configuration (length, thickness) of the load line is changed, the resistance value r must be derived and registered again, which is extremely time-consuming.

Furthermore, the power supply device in Patent Document 2 is configured to recognize the voltage drop on the load line based on the value of the output current I, so it is unable to accurately grasp the actual voltage drop. For example, if the value of the output current I increases, it is expected that the load line will self-heat, causing the resistance value r to fluctuate (increase). Furthermore, because the load line contains an inductance component in addition to the resistance component, it is expected that when the output current I suddenly changes, voltage fluctuations will occur due to the back electromotive force of the inductance component.

In the power supply device of Patent Document 2, as shown in the graph in Figure 15(a), when the output current I = zero, it is controlled so that V2m = V1m [operating point P0], and when I = Ia flows, it is controlled so that V2m = V1m + Ia・r [operating point P1]. Therefore, as shown in the time chart in Figure 15(b), when there is a sudden change from I = zero to I = Ia, I, V2m, and V2 change in the same way, and each waveform becomes approximately similar.

At this time, as shown by the waveform of the voltage drop V2-V1 on the load line, immediately after the output current I suddenly changes, a voltage fluctuation ΔVx caused by the inductance component occurs on the load line. However, this voltage fluctuation ΔVx is not reflected in the control, so the waveform of the load end voltage V1 will be disrupted for the period until the voltage fluctuation ΔVx converges.

Furthermore, when current Ia begins to flow through the load line, the load line self-heats, gradually increasing its resistance, resulting in a voltage fluctuation ΔVy. However, this voltage fluctuation ΔVy is not reflected in the control, so the load end voltage V1 gradually decreases until the load line temperature stabilizes. For example, if resistance value r is registered so that V1 = V1m when I is small, V1 ≠ V1m when I is large, and if resistance value r is registered so that V1 = V1m when I is large, V1 ≠ V1m when I is small. Therefore, even when using the power supply device described in Patent Document 2, it is difficult to accurately control the load end voltage.

The present invention was made in consideration of the above-mentioned background art, and aims to provide a switching power supply device that can accurately control load-end voltage using a feedforward remote sensing function, and a power supply system using the same.

The invention described in claim 1 is
a power conversion unit that converts a DC or AC input voltage supplied to an input terminal into a DC voltage by a switching operation of a main switching element and supplies the power to a load through a load line of a predetermined length;
an output terminal voltage detection unit that detects an output terminal voltage Vo generated at the output terminal of the power conversion unit and outputs a corresponding analog output terminal detection voltage Vok=k·Vo (k is a positive constant);
a load end voltage detection unit that detects a load end voltage Vf generated at the load end of the load line and outputs a corresponding analog load end detection voltage Vfk=k·Vf;
a designated voltage information generating unit that receives a designated value Vfs of the load end voltage Vf and generates designated voltage information J(Vsi) indicating a corresponding designated voltage Vsi=k·Vfs;
a target voltage information generating unit that performs digital calculation processing based on the output end detected voltage Vok, the load end detected voltage Vfk, and the specified voltage information J(Vsi) to generate target voltage information J(Vm) indicating a target voltage Vm=Vsi+Vok−Vfk;
a target voltage generation unit that generates an analog target voltage Vm based on the target voltage information J(Vm);
a control unit that determines the on-time and off-time of the main switching element so that the output terminal detected voltage Vok and the target voltage Vm are equal, generates drive pulses so that the main switching element is turned on and off during these on-times and off-times, and outputs the drive pulses to the main switching element.

The target voltage generation unit preferably comprises a pulse width modulation unit that outputs a square wave voltage whose duty is set based on the target voltage information J(Vm), and a low-pass filter that smooths the square wave voltage to generate the target voltage Vm [the invention described in claim 2].

The target voltage information creation unit can be configured to perform processing in a first information creation mode to create the target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk when Vok - Vfk < Vth (Vth is a voltage threshold), and to perform processing in a second information creation mode to create target voltage information J(Vm) such that Vm = Vsi + Vth when Vok - Vf ≥ Vth [the invention described in claim 3].

Alternatively, the target voltage information creation unit can be configured to perform processing in a first information creation mode that creates the target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk when Vok - Vfk < Vth (Vth is a voltage threshold), and to perform processing in a second information creation mode that creates the target voltage information J(Vm) such that Vm = Vsi when Vok - Vfk ≥ Vth [the invention described in claim 4].

Alternatively, the target voltage information creation unit can be configured to perform processing in a first information creation mode that creates the target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk when Vfk > Vth (Vth is a voltage threshold), and to perform processing in a second information creation mode that creates the target voltage information J(Vm) such that Vm = Vsi when Vfk ≤ Vth, regardless of the value of Vok - Vfk [the invention described in claim 5].

Furthermore, it is preferable that the designated voltage information creating unit is configured so that the designated value Vfs of the load end voltage Vf can be changed externally [the invention according to claim 6].
a power conversion unit that converts a DC or AC input voltage supplied to an input terminal into a DC voltage by a switching operation of a main switching element and supplies the power to a load through a load line of a predetermined length;
an output terminal voltage detection unit that detects an output terminal voltage Vo generated at the output terminal of the power conversion unit and outputs a corresponding analog output terminal detection voltage Vok=k·Vo (k is a positive constant);
a load end voltage detection unit that detects a load end voltage Vf generated at the load end of the load line and outputs a corresponding analog load end detection voltage Vfk=k·Vf;
a designated voltage information generating unit that receives a designated value Vfs of the load end voltage Vf and generates designated voltage information J(Vsi) indicating a corresponding designated voltage Vsi=k·Vfs;
a temporary target voltage information generating unit that performs digital calculation processing based on the output end detected voltage Vok, the load end detected voltage Vfk, and the specified voltage information J(Vsi) to generate temporary target voltage information J(Vmx) indicating a temporary target voltage Vmx=h·(Vsi+Vok−Vfk) (h is a positive constant);
a target voltage generating unit that generates an analog target voltage Vm=Vmx/h based on the temporary target voltage information J(Vmx);
a control unit that determines an on-time and an off-time of the main switching element so that the output terminal detected voltage Vok is equal to the target voltage Vm, generates a drive pulse so that the main switching element is turned on and off during the on-time and off-time, and outputs the drive pulse to the main switching element;
a Vm line external connection terminal that enables a Vm line, which is an output line of the target voltage generation unit, to be connected to an external device;
The target voltage generation unit is a switching power supply device that includes a temporary target voltage generation unit that generates an analog temporary target voltage Vmx based on the temporary target voltage information J(Vmx) created by the temporary target voltage information creation unit, a pull-up circuit that pulls up the Vm line to a positive voltage, and a Vm control unit that has a current-drawing output stage and draws current from the Vm line when Vm > Vmx/h and stops drawing current from the Vm line when Vm ≦ Vmsx/h, thereby controlling the target voltage Vm to be a value Vmx/h that corresponds to the temporary target voltage Vmx.

The temporary target voltage generation unit preferably comprises a pulse width modulation unit that outputs a square wave voltage whose duty is set based on the temporary target voltage information J(Vmx), and a low-pass filter that smooths the square wave voltage to generate the temporary target voltage Vmx [the invention described in claim 8].

Furthermore, it is preferable that the specified voltage information creation unit is configured so that the specified value Vfs of the load end voltage Vf can be changed externally [the invention described in claim 9].

The temporary target voltage information creation unit can be configured to perform processing in a first information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h (Vsi + Vok - Vfk) in the range of Vok - Vfk < Vth (Vth is a voltage threshold), and to perform processing in a second information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h (Vsi + Vth) in the range of Vok - Vf ≥ Vth [the invention described in claim 10].

Alternatively, the temporary target voltage information creation unit can be configured to perform processing in a first information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h·(Vsi + Vok−Vfk) in the range of Vok−Vfk<Vth (Vth is a voltage threshold), and to perform processing in a second information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h·Vsi in the range of Vok−Vfk≧Vth [the invention described in claim 11].

Alternatively, the temporary target voltage information creation unit can be configured to perform processing in a first information creation mode that creates the temporary target voltage information J(Vmx) such that Vmx = h·(Vsi + Vok−Vfk) in the range of Vfk>Vth (Vth is a voltage threshold), and to perform processing in a second information creation mode that creates the temporary target voltage information J(Vmx) such that Vmx = h·Vsi in the range of Vfk≦Vth, regardless of the value of Vok−Vfk [the invention described in claim 12].

Furthermore, it is preferable that the specified voltage information creation unit is configured so that the specified value Vfs of the load end voltage Vf can be changed externally [the invention described in claim 13].

Furthermore, the present invention is directed to a power supply system using a plurality of switching power supply devices according to the present invention, comprising:
In each of the switching power supply devices, the output ends of the power conversion units are connected in parallel with each other, the Vm line external connection terminals are connected with each other, the constant k is set to a uniform value, and the constant h is set to a uniform value;
When one of the switching power supply devices having the lowest designated value Vfs of the load end voltage Vf is designated as a master power supply and the others are designated as slave power supplies,
the load end voltage detection unit of the master power supply has an input end connected to the load end, detects the load end voltage Vf, and outputs the load end detection voltage Vfk;
the input terminal of the load end voltage detection unit of the slave power supply is open and outputs zero volts regardless of the value of the load end voltage Vf, which causes the temporary target voltage information creation unit of the slave power supply to create the temporary target voltage information J(Vmx) in the second information creation mode,
a target voltage Vm(M) is generated on the Vm line of the master power supply, the target voltage Vm being generated by the target voltage generation unit of the master power supply itself, and the target voltage Vm(M) input via the external connection terminal of the Vm line of the slave power supply itself is generated on the Vm line of the slave power supply itself;
The control units of the master power supply and the slave power supply are a power supply system that generates the drive pulses so as to reduce the difference between the target voltage Vm(M) generated on its own Vm line and its own output terminal detected voltage Vok.

The switching power supply device of the present invention uses a unique feedforward remote sensing function to accurately match the load end voltage Vf to a specified value Vfs. Furthermore, by operating the target voltage information creation unit or temporary target voltage information creation unit normally in the first information creation mode and in the second information creation mode in special circumstances, it is possible to continue supplying power to the load while ensuring the safety of the load and power conversion unit, even in the event that the sensing line suddenly becomes disconnected (e.g., due to a wire breakage).

The power supply system of the present invention operates the above-mentioned switching power supply units in parallel, and by controlling the target voltage Vm of one of the multiple switching power supply units, it performs feedforward remote sensing while meeting requirements such as simultaneous startup of all switching power supply units, equalization of load power burden, and easy setting changes to the load end voltage Vf.

1 is a block diagram showing a configuration of a switching power supply device according to a first embodiment of the present invention; 2A and 2B are circuit diagrams showing an example of a method for inputting an external command GS (load end voltage specification value Vfs) to the specification voltage information creation unit of FIG. 1 , and FIG. 2C and 2D are circuit diagrams showing a specific example of the configuration of the target voltage generation unit of FIG. 1 . 2A is a graph showing the processing content of the target voltage information creation unit in FIG. 1 , and FIG. 2B is a time chart showing the operating waveforms [operating point P0→P1] of each part of the switching power supply device when this processing is executed. 2A is a graph showing the processing content of a first modified example of the target voltage creation unit in FIG. 1 , and FIG. 2B is a time chart showing the operating waveforms [operating point P1→P2] of each part of the switching power supply device when this processing is executed. 1A is a graph showing the processing content of a second modified example of the target voltage creation unit of FIG. 1 , and FIG. 1B is a time chart showing the operating waveforms [operating point P1→P3] of each part of the switching power supply device when this processing is executed. 10A is a graph showing the processing content of a third modified example of the target voltage creation unit in FIG. 1 , and FIG. 10B is a time chart showing the operating waveforms [operating point P1→P4] of each part of the switching power supply device when this processing is executed. FIG. 10 is a block diagram showing the configuration of a switching power supply device according to a second embodiment of the present invention. 8A is a circuit diagram showing a specific example of the configuration of the target voltage generating unit in FIG. 7, and FIG. 8B is a circuit diagram showing a modified example of the temporary target voltage generating unit. 8A is a graph showing the processing content of the temporary target voltage information creating unit in FIG. 7, and FIG. 8B is a time chart showing the operating waveforms [operating point P0→P1] of each part of the switching power supply device when this processing is executed. 8A is a graph showing the processing content of the temporary target voltage information creating unit in FIG. 7, and FIG. 8B is a time chart showing the operating waveforms [operating point P1→P2] of each part of the switching power supply device when this processing is executed. 8A is a graph showing the processing content of a first modified example of the temporary target voltage information creation unit of FIG. 7, and FIG. 8B is a time chart showing the operating waveforms [operating point P1→P3] of each part of the switching power supply device when this processing is executed. 8A is a graph showing the processing content of a second modified example of the temporary target voltage information creation unit of FIG. 7, and FIG. 8B is a time chart showing the operating waveforms [operating point P1→P4] of each part of the switching power supply device when this processing is executed. 1 is a block diagram showing a configuration of an embodiment of a power supply system of the present invention; 14 is a circuit diagram showing the operation of each target voltage generating unit of the master power supply and the slave power supply in the power supply system of FIG. 13. 1A is a graph showing the processing executed in a conventional switching power supply device (the power supply device of Patent Document 2), and FIG. 1B is a time chart showing the operating waveforms [operating point P0→P1] of each part of the switching power supply device when this processing is executed.

<<First embodiment of the switching power supply device of the present invention>>
A first embodiment of a switching power supply device according to the present invention will now be described with reference to FIGS.
<Switching power supply device 10 of the first embodiment>
The switching power supply 10 of this embodiment has an input power supply 14 connected to an input terminal 12, and includes a power conversion unit 20 that converts a DC or AC input voltage Vi supplied to the input terminal 12 into a DC voltage by the switching operation of a main switching element (not shown), and supplies the power to a load 18 through a load line 16 of a predetermined length (e.g., 1 m to 20 m).In addition, as shown in FIG. 1, the switching power supply 10 includes an output terminal voltage detection unit 24, a load terminal voltage detection unit 26, a specified voltage information creation unit 28, a target voltage information creation unit 30, a target voltage generation unit 32, and a control unit 34.

The output terminal voltage detection unit 24 is connected to the output terminal 22 of the power conversion unit 20. It detects the output terminal voltage Vo generated at the output terminal 22 and outputs a corresponding analog output terminal detection voltage Vok = k · Vo (k is a positive constant). The output terminal voltage detection unit 24 can be configured using a known voltage amplifier circuit or differential amplifier circuit.

The load end voltage detection unit 26 is connected to one end (load end 36) of the load line 16 via a sensing line 38. It detects the load end voltage Vf generated at the load end 36 and outputs a corresponding analog load end detection voltage Vfk = k·Vf (where the constant k is the same value as the constant k of the output end voltage detection unit 24). The load end voltage detection unit 26 is preferably configured as a differential amplifier circuit to match the ground potential of the load end detection voltage Vfk to the output end detection voltage Vok.

The specified voltage information creation unit 28 is provided within the digital processor. The specified value Vfs of the load end voltage Vf is set as the default value, and this block creates specified voltage information J (Vsi) indicating the corresponding specified voltage Vsi = k·Vfs (where the constant k is the same value as the constant k of the output end voltage detection unit 24).

The specified voltage information creation unit 28 is configured so that the setting of the specified value Vfs can be changed by an external command GS from the user. For example, if the specified value Vfs is set to 48 V by default and the user wants to change the specified value Vfs to 48.5 V, the setting is changed by inputting the external command GS. There are various methods for inputting the external command GS. For example, as shown in Figure 2(a), the user can input it as a digital signal via an external control device 40 externally connected to the switching power supply 10. Alternatively, as shown in Figure 2(b), the user can manually adjust the variable resistor 42a of the voltage variable circuit 42 provided inside the switching power supply 10 and input it as an analog voltage.

The target voltage information creation unit 30 is a block located within the digital processor that performs digital calculations based on the output end detected voltage Vok, the load end detected voltage Vf, and the specified voltage information J(Vsi) to create target voltage information J(Vm) that indicates the target voltage Vm = Vsi + Vok - Vfk. The processing performed by the target voltage information creation unit 30 can be represented as shown in the graph in Figure 3(a).

The target voltage generation unit 32 is a block that generates an analog target voltage Vm based on target voltage information J(Vm). For example, as shown in Figure 2(c), the target voltage generation unit 32 can be configured simply with a single D/A converter. Alternatively, as shown in Figure 2(d), the target voltage generation unit 32 can be configured with a pulse width modulation unit 32a that outputs a square-wave voltage Vp (peak value V1) whose duty cycle D is set based on the target voltage information J(Vm), and a low-pass filter 32b that smooths the square-wave voltage Vp to generate a target voltage Vm ≈ V1 · D. Note that when using a D/A converter, a relatively expensive, high-speed digital processor is required to increase the resolution of the target voltage Vm. However, a configuration with a pulse width modulation unit 32a and low-pass filter 32b has the advantage of being able to generate a target voltage Vm with high resolution even using an inexpensive, general-purpose digital processor.

The control unit 34 is a block that determines the on-time and off-time of the main switching element so that the output terminal detection voltage Vok is equal to the target voltage Vm, generates a drive pulse Vg so that the main switching element turns on and off during these on-time and off-time, and outputs it to the main switching element.

Next, the operation of the switching power supply 10 will be explained based on the time chart in Figure 3(b). Figure 3(b) shows the operating waveforms when the load 18 suddenly changes and the output current becomes Io = Ia [operating point P1] while the switching power supply 10 is operating at output current Io = zero [operating point P0].

First, to explain the operation of operating point P0, since the output current Io = zero, the voltage drop Vo - Vf on the load line 16 becomes zero. As a result, Vok - Vfk = zero, so the target voltage information creation unit 30 and target voltage generation unit 32 operate to generate the target voltage Vm = Vsi. As a result, the control unit 34 operates so that the output end voltage Vo becomes Vo = Vm/k = Vok/k = Vsi/k = Vfs, and the load end voltage Vf becomes Vf = Vo = Vfs. In other words, the load end voltage Vf is controlled to the same value as the specified value Vfs.

When the output current Io suddenly increases from zero to Ia between times ta and tb, the operating point changes from P0 to P1. At operating point P1, the output current Io = Ia, so the voltage drop Vo - Vf on the load line 16 is a finite value. As a result, Vok - Vfk is a finite value, so the target voltage information creation unit 30 and target voltage generation unit 32 operate, generating the target voltage Vm = Vsi + Vok - Vfk. As a result, the control unit 34 operates to set the output end voltage Vo as Vo = Vm/k = Vok/k = (Vsi + Vok - Vfk)/k = Vfs + (Vok - Vfk)/k, and the load end voltage Vf is Vf = Vfs. In other words, the load end voltage Vf is controlled to the same value as the specified value Vfs.

In Figure 3(b), immediately after the operating point P1 is reached, a voltage fluctuation ΔVx occurs in the waveform of the voltage drop Vo-Vf due to the inductance component of the load line 16. However, the target voltage Vm changes in response to this voltage fluctuation ΔVx, appropriately changing the output terminal voltage Vo. Furthermore, after the operating point P1 is reached, a voltage fluctuation ΔVy occurs as the load line 16 self-heats and its resistance increases, but the target voltage Vm changes in response to this voltage fluctuation ΔVy, appropriately changing the output terminal voltage Vo. Therefore, the load terminal voltage Vf is controlled to approximately the specified value Vfs, even when voltage fluctuations ΔVx and ΔVy occur.

In this way, with the switching power supply device 10, the output terminal voltage Vo changes appropriately in response to the voltage drop in the load line 16, allowing the load terminal voltage Vf to accurately match the specified value Vfs.

<Modifications 30(1) to 30(3) of the target voltage information generating unit 30>
When the target voltage information creating unit 30 is used, if the sensing line 38 suddenly becomes disconnected (for example, due to a disconnection accident), Vok-Vfk becomes large even though the actual voltage drop Vo-Vf in the load line 16 is small, and the target voltage Vm becomes higher than expected. As a result, the control unit 34 operates, causing the output end voltage Vo and the load end voltage Vf to become excessively large, and it is conceivable that the safety of the load 18 and the power conversion unit 20 cannot be ensured.

For example, for safety reasons, adding an overvoltage protection circuit to stop the power conversion unit 20 is one possible method, but depending on the type of load 18, it may not be possible to simply stop the power supply. Therefore, when a malfunction occurs in which the sensing line 38 suddenly becomes disconnected, it is necessary to continue the power supply to the load 18 while ensuring the safety of the load 18, etc.

By using the modified target voltage information creation units 30(1) to 30(3) described below, if the sensing line 38 suddenly becomes disconnected, the load end voltage Vf will be maintained at a value that does not deviate significantly from the specified value Vfs, thereby resolving the above problem.

First, the target voltage information creation unit 30(1) of the first modified example will be described. A voltage threshold Vth is set in advance in the target voltage information creation unit 30(1). Then, as shown in FIG. 4(a), processing is performed in a first information creation mode to create target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk in the range of Vok - Vfk < Vth. The first information creation mode is the same as the processing content of the target voltage information creation unit 30 described above [FIG. 3(a)]. Then, in the range of Vok - Vf ≧ Vth, processing is performed in a second information creation mode to create target voltage information J(Vm) such that Vm = Vsi + Vth.

To explain the operation of the switching power supply 10 when using the target voltage information creation unit 30(1), the time chart in Figure 4(b) shows the operating waveforms when, while operating in the range Vok - Vfk < Vth [operating point P1], the sensing line 38 is disconnected for some reason, causing the device to operate in the range Vok - Vfk ≥ Vth [operating point P2]. Here, it is assumed that the output current Io is constant.

Because operating point P1 performs processing in the first information creation mode, the voltages of each component are the same as those at operating point P1 in Figure 3(b). When sensing line 38 breaks at time tc, load end detection voltage Vfk decreases and Vok - Vfk increases between times tc and td, causing target voltage information creation unit 30 and target voltage generation unit 32 to operate and increase target voltage Vm. As a result, the output end voltage Vo and load end voltage Vf increase due to the operation of control unit 34.

Then, at time td, the range Vok - Vfk ≧ Vth [operating point P2] is reached, and the mode switches from the first information creation mode to the second information creation mode. In other words, after time td, the increase in target voltage Vm is limited, and Vm is maintained at Vsi + Vth. As a result, the control unit 34 controls the output terminal voltage Vo to Vo = Vm/k = Vok/k = (Vsi + Vth)/k = Vfs + Vth/k, and the load terminal voltage Vf is maintained at a value slightly lower than the output terminal voltage Vo. Therefore, by setting the voltage threshold Vth to an appropriate value, it is possible to continue supplying power to the load 18 while ensuring the safety of the load 18, etc.

Next, the target voltage information creation unit 30(2) of the second modified example will be described. A voltage threshold Vth is set in advance in the target voltage information creation unit 30(2). Then, as shown in FIG. 5(a), processing is performed in a first information creation mode to create target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk in the range of Vok - Vfk < Vth. This first information creation mode is the same as the processing content of the target voltage information creation unit 30 described above [FIG. 3(a)]. Then, in the range of Vok - Vf ≧ Vth, processing is performed in a second information creation mode to create target voltage information J(Vm) such that Vm = Vsi.

To explain the operation of the switching power supply 10 when using the target voltage information creation unit 30(2), the time chart in Figure 5(b) shows the operating waveforms when, while operating in the range Vok - Vfk < Vth [operating point P1], the sensing line 38 is disconnected for some reason, causing the device to operate in the range Vok - Vfk ≥ Vth [operating point P3]. Here, it is assumed that the output current Io is constant.

Because operating point P1 performs processing in the first information creation mode, the voltages of each component are the same as those at operating point P1 in Figure 3(b). When sensing line 38 breaks at time te, load end detection voltage Vfk decreases and Vok - Vfk increases between times te and tf, causing target voltage information creation unit 30 and target voltage generation unit 32 to operate and increase target voltage Vm. As a result, the output end voltage Vo and load end voltage Vf increase due to the operation of control unit 34.

Then, at time tf, the range Vok - Vfk ≥ Vth [operating point P3] is reached, and the mode switches from the first information creation mode to the second information creation mode. In other words, after time tf, the increase in target voltage Vm is limited, and Vm = Vsi is maintained. As a result, the control unit 34 operates to control the output terminal voltage Vo to Vo = Vm/k = Vok/k = Vsi/k = Vfs slightly after the change in Vm, and the load terminal voltage Vf is maintained at a value slightly lower than the output terminal voltage Vo (= Vfs). Therefore, power supply to the load 18 can be continued while ensuring the safety of the load 18, etc.

Next, the target voltage information creation unit 30(3) of the third modified example will be described. A voltage threshold Vth is set in advance in the target voltage information creation unit 30(3). Then, as shown in FIG. 6(a), processing is performed in a first information creation mode to create target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk in the range of Vfk > Vth. This first information creation mode is the same as the processing content of the target voltage information creation unit 30 described above [FIG. 3(a)]. Then, in the range of Vfk ≦ Vth, processing is performed in a second information creation mode to create target voltage information J(Vm) such that Vm = Vsi, regardless of the value of Vok - Vfk.

To explain the operation of the switching power supply 10 when using the target voltage information creation unit 30(3), the time chart in Figure 6(b) shows the operating waveforms when, while operating in the range Vfk > Vth [operating point P1], the sensing line 38 is broken for some reason, causing the device to operate in the range Vfk <= Vth [operating point P4]. Here, it is assumed that the output current Io is constant.

Because operating point P1 performs processing in the first information creation mode, the voltages of each component are the same as those at operating point P1 in Figure 3(b). When sensing line 38 breaks at time tg, load end detection voltage Vfk decreases and Vok - Vfk increases between times tg and th, causing target voltage information creation unit 30 and target voltage generation unit 32 to operate and increase target voltage Vm. As a result, control unit 34 operates, increasing output end voltage Vo and load end voltage Vf.

Then, at time th, the range Vfk≦Vth [operating point P4] is reached, and the mode switches from the first information creation mode to the second information creation mode. In other words, after time th, the increase in target voltage Vm is limited, and Vm is maintained at Vsi. As a result, the control unit 34 operates to control the output terminal voltage Vo to Vo=Vm/k=Vok/k=Vsi/k=Vfs slightly after the change in Vm, and the load terminal voltage Vf is maintained at a value slightly lower than the output terminal voltage Vo (=Vfs). Therefore, power supply to the load 18 can be continued while ensuring the safety of the load 18, etc.

<Summary of Effects of Switching Power Supply Device 10 and Modifications>
As described above, switching power supply 10 can accurately match load end voltage Vf to specified value Vfs by using a unique feedforward remote sensing function. Furthermore, by using modified target voltage information creation units 30(1) to 30(3) to normally operate in the first information creation mode and in the second information creation mode at special times, it is possible to continue supplying power to load 18 while ensuring the safety of load 18 and power conversion unit 20, even when an incident occurs in which the sensing line is suddenly disconnected (for example, a wire breakage accident).

<<Second embodiment of the switching power supply device of the present invention>>
Next, a second embodiment of the switching power supply of the present invention will be described with reference to Figures 7 to 12. Here, the same components as those in the switching power supply 10 described above will be given the same reference numerals and the description thereof will be omitted.
<Switching power supply device 44 of the second embodiment>
The switching power supply 44 of this embodiment is a power supply that has a remote sensing function and a function suitable for parallel operation and can be used as a standalone power supply. As shown in Figure 7, the configuration of the switching power supply 44 has many similarities to that of the switching power supply 10, but differs in that a temporary target voltage information generator 46 is provided instead of the target voltage information generator 30, a target voltage generator 48 is provided instead of the target voltage generator 32, and a Vm line external connection terminal 50 is newly provided. The following description will focus on the differences in configuration.

The temporary target voltage information creation unit 46 is a block located within the digital processor that performs digital calculations based on the output terminal detected voltage Vok, the load terminal detected voltage Vf, the specified voltage information J(Vsi), and a preset voltage threshold Vth to create temporary target voltage information J(Vmx) indicating the temporary target voltage Vmx. Specifically, in the range of Vok - Vfk < Vth (Vth is the voltage threshold), it performs processing in a first information creation mode to create target voltage information J(Vmx) such that Vmx = h (Vsi + Vok - Vfk). In the range of Vok - Vf ≥ Vth, it performs processing in a second information creation mode to create temporary target voltage information J(Vmx) such that Vmx = h (Vsi + Vth). The processing performed by the temporary target voltage information creation unit 46 can be represented as shown in the graphs in Figures 9(a) and 10(a).

The first information creation mode is a mode that is executed when the switching power supply 44 is operating normally, and the second information creation mode is a mode that is executed when an event occurs in which the sensing line 38 suddenly becomes disconnected (for example, a wire breakage accident). This has the same meaning as the first and second information creation modes described in the explanation of the switching power supply 10.

The target voltage generation unit 48 is a block that generates an analog target voltage Vm = Vmx/h based on the temporary target voltage information J(Vmx). As shown in Figure 8(a), the target voltage generation unit 48 is composed of a temporary target voltage generation unit 52, a pull-up circuit 54, and a Vm control unit 56.

The temporary target voltage generator 52 generates an analog temporary target voltage Vmx based on the temporary target voltage information J(Vmx). The temporary target voltage generator 52 can be configured similarly to the target voltage generator 32 shown in Figures 2(c) and (d). That is, as shown in Figure 8(a), it can be configured simply with a single D/A converter. Alternatively, as shown in Figure 8(b), it can be configured with a pulse-width modulator 52a that outputs a square-wave voltage Vp (peak value V1) whose duty cycle D is set based on the temporary target voltage information J(Vmx), and a low-pass filter 58b that smooths the square-wave voltage Vp to generate a temporary target voltage Vmx ≈ V1 · D. Note that a D/A converter configuration requires a relatively expensive, high-speed digital processor to achieve high resolution for the temporary target voltage Vmx. However, a configuration with a pulse-width modulator 52a and a low-pass filter 52b offers the advantage of being able to generate a temporary target voltage Vmx with high resolution even using an inexpensive, general-purpose digital processor.

The pull-up circuit 54 is a circuit that pulls up the output line of the Vm control unit 56 (described below, the Vm line 50a, which is the output line of the target voltage generation unit 48) to a positive voltage. The pull-up circuit 54 is a constant current circuit, as shown in Figure 8 (a). The pull-up circuit may simply be a fixed resistor, but a constant current circuit has the advantage of reducing loss.

The Vm control unit 56 has a current-drawing output stage, and is a block that draws current from the Vm line 50a when Vm > Vmx/h (constant h is the same value as the constant h of the temporary target voltage information creation unit 46), and stops drawing current from the Vm line 50a when Vm ≤ Vmx/h, thereby controlling the target voltage Vm on the Vm line 50a to a value Vmx/h corresponding to the temporary target voltage Vmx. For example, in the configuration of Figure 8(a), Vm is controlled to (1 + R1/R2) Vmx, and if R2 is left open, Vm is controlled to Vmx.

The Vm line external connection terminal 50 is a terminal that allows the Vm line 50a to be connected externally. This terminal is connected to each other when multiple switching power supply units 44 are operated in parallel, and is left open when using a single switching power supply unit 44.

Next, the operation of the switching power supply 44 when used alone will be explained with reference to Figures 9(b) and 10(b). The time chart in Figure 9(b) shows the operating waveforms when the load 18 suddenly changes and the output current becomes Io = Ia [operating point P1] while operating at output current Io = zero [operating point P0].

First, to explain the operation of operating point P0, since the output current Io = zero, the voltage drop Vo - Vf on the load line 16 becomes zero. As a result, Vok - Vfk = zero, so the temporary target voltage information creation unit 46 and target voltage generation unit 48 operate to generate the target voltage Vm = Vmx/h = (h · Vsi)/h = Vsi. As a result, the control unit 34 operates so that the output end voltage Vo becomes Vo = Vm/k = Vok/k = Vsi/k = Vfs, and the load end voltage Vf becomes Vf = Vo = Vfs. In other words, the load end voltage Vf is controlled to the same value as the specified value Vfs.

When the output current Io suddenly increases from zero to Ia between times ta and tb, the operating point changes from P0 to P1. At operating point P1, the output current Io = Ia, so the voltage drop Vo - Vf on the load line 16 is a finite value. As a result, Vok - Vfk is a finite value, so the temporary target voltage information creation unit 46 and target voltage generation unit 48 operate, generating the target voltage Vm = Vmx/h = [h · (Vsi + Vok - Vfk)]/h = Vsi + Vok - Vfk. As a result, the control unit 34 operates to set the output end voltage Vo as Vo = Vm/k = Vok/k = (Vsi + Vok - Vfk)/k = Vfs + (Vok - Vfk)/k, and the load end voltage Vf is Vf = Vfs. In other words, the load end voltage Vf is controlled to the specified value Vfs.

In this way, when the switching power supply device 44 is operating normally [at operating points P0, P1 in the range Vok - Vfk < Vth], the temporary target voltage information creation unit 46 performs processing in the first information creation mode, causing the output end voltage Vo to change appropriately in response to the voltage drop on the load line 16, and enabling the load end voltage Vf to accurately match the specified value Vfs.

The time chart in Figure 10(b) shows the operating waveforms when, while operating in the range Vok - Vfk < Vth [operating point P1], the sensing line 38 is disconnected for some reason, causing the device to operate in the range Vok - Vfk ≥ Vth [operating point P2]. Here, it is assumed that the output current Io is constant.

Operation at operating point 1 in Figure 10(b) is the same as operation point P1 in Figure 9(b). When the sensing line 38 is disconnected at time tc while at operating point P1, the load end detection voltage Vfk decreases and Vok - Vfk increases between times tc and td. This causes the temporary target voltage information creation unit 46 and target voltage generation unit 48 to operate, increasing the temporary target voltage Vmx and target voltage Vm = Vmx/h. As a result, the output end voltage Vo and load end voltage Vf increase due to the operation of the control unit 34.

Then, at time td, the range Vok - Vfk ≥ Vth [operating point P2] is reached, and the mode switches from the first information creation mode to the second information creation mode. In other words, after time td, the increase in the temporary target voltage Vmx and the target voltage Vm is limited, and they are maintained at Vmx = h · (Vsi + Vth) and Vm = Vsi + Vth, respectively. As a result, the control unit 34 controls the output terminal voltage Vo to Vo = Vm/k = Vok/k = (Vsi + Vth)/k = Vfs + Vth/k, and the load terminal voltage Vf is maintained at a value slightly lower than the output terminal voltage Vo. Therefore, by setting the voltage threshold Vth to an appropriate value, it is possible to continue supplying power to the load 18 while ensuring the safety of the load 18, etc.

Note that the operation of switching power supply device 44 shown in Figure 9(b) is basically the same as the operation of switching power supply device 10 shown in Figure 3(b), and the operation of switching power supply device 44 shown in Figure 10(b) is basically the same as the operation of switching power supply device 10 shown in Figure 4(b). The difference is that switching power supply device 44 is characterized by the inclusion of constant h in the processing and operation of temporary target voltage information creation unit 46 and target voltage generation unit 48, which provides a unique effect when performing parallel operation. More details will be provided later in the explanation of power supply system 58.

<Modifications 46(1), 46(2) of the temporary target voltage information generating unit 46>
Next, two modified examples 46(1) and 46(2) in which the processing content of the second information creation mode of the temporary target voltage information creation unit 46 is changed will be described in order.

First, the temporary target voltage information creation unit 46(1) of the first modified example will be described. The temporary target voltage information creation unit 46(1) performs processing in a first information creation mode to create target voltage information J(Vmx) such that Vmx = h·(Vsi + Vok−Vfk) in the range of Vok−Vfk<Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create temporary target voltage information J(Vmx) such that Vmx = h·Vsi in the range of Vok−Vf≧Vth. The processing performed by the temporary target voltage information creation unit 46(1) can be represented as shown in the graph in FIG. 11(a).

The time chart in Figure 11(b) shows the operating waveforms when, while operating in the range Vok - Vfk < Vth [operating point P1], the sensing line 38 is disconnected for some reason, causing the device to operate in the range Vok - Vfk ≥ Vth [operating point P3]. Here, it is assumed that the output current Io is constant.

The operation of operating point 1 in Figure 11(b) is the same as the operation of operating point P1 in Figure 9(b). When the sensing line 38 breaks at time te, the load end detection voltage Vfk decreases and Vok - Vfk increases between times te and tf. This causes the temporary target voltage information creation unit 46(1) and target voltage generation unit 48 to operate, increasing the temporary target voltage Vmx and target voltage Vm = Vmx/h. As a result, the output end voltage Vo and load end voltage Vf increase due to the operation of the control unit 34.

Then, at time tf, the range Vok - Vfk ≧ Vth [operating point P3] is reached, and the mode switches from the first information creation mode to the second information creation mode. In other words, after time tf, the increase in the temporary target voltage Vmx and the target voltage Vm is limited, and they are maintained at Vmx = h · Vsi and Vm = Vsi, respectively. As a result, the output end voltage Vo is controlled by the control unit 34 so that Vo = Vm/k = Vok/k = Vsi/k = Vfs, and the load end voltage Vf is maintained at a value slightly lower than the output end voltage Vo. Therefore, the power supply to the load 18 can be continued while ensuring the safety of the load 18, etc.

The operation of the switching power supply 44 shown in Figure 11(b) is basically the same as the operation of the switching power supply 10 shown in Figure 5(b).

Next, the temporary target voltage information creation unit 46(2) of the second modified example will be described. The temporary target voltage information creation unit 46(2) performs processing in a first information creation mode to create target voltage information J(Vmx) such that Vmx = h·(Vsi + Vok−Vfk) in the range of Vfk > Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create temporary target voltage information J(Vmx) such that Vmx = h·Vsi in the range of Vf≦Vth, regardless of the value of Vok−Vfk. The processing performed by the temporary target voltage information creation unit 46(2) can be represented as shown in the graph in FIG. 12(a).

The time chart in Figure 12(b) shows the operating waveforms when, while operating in the range Vfk > Vth [operating point P1], the sensing line 38 is disconnected for some reason, causing the device to operate in the range Vfk <= Vth [operating point P4]. Here, it is assumed that the output current Io is constant.

The operation of operating point 1 in Figure 12(b) is the same as the operation of operating point P1 in Figure 9(b). When the sensing line 38 breaks at time tg, the load end detected voltage Vfk decreases and Vok - Vfk increases between times tg and th. This causes the temporary target voltage information creation unit 46(1) and target voltage generation unit 48 to operate, increasing the temporary target voltage Vmx and target voltage Vm = Vmx/h. As a result, the output end voltage Vo and load end voltage Vf increase due to the operation of the control unit 34.

Then, at time th, the range Vfk≦Vth [operating point P4] is reached, and the mode switches from the first information creation mode to the second information creation mode. In other words, after time th, the increase in the temporary target voltage Vmx and the target voltage Vm is limited, and they are maintained at Vmx = h·Vsi and Vm = Vsi, respectively. As a result, the control unit 34 operates to control the output end voltage Vo to Vo = Vm/k = Vok/k = Vsi/k = Vfs, and the load end voltage Vf is maintained at a value slightly lower than the output end voltage Vo. Therefore, power supply to the load 18 can be continued while ensuring the safety of the load 18, etc.

The operation of the switching power supply 44 shown in Figure 12(b) is basically the same as the operation of the switching power supply 10 shown in Figure 6(b).

<Summary of Effects of Switching Power Supply Device 44 and Modifications>
As described above, switching power supply device 44 provides the same operational effects as switching power supply device 10. Furthermore, switching power supply device 44 has an additional function suitable for parallel operation, and by combining multiple switching power supply devices 44, a power supply system with excellent performance can be obtained. This will be described in more detail later in the description of power supply system 58.

<<One embodiment of the power supply system of the present invention>>
Next, one embodiment of the power supply system of the present invention will be described with reference to Figures 13 and 14. As shown in Figure 13, the power supply system 58 of this embodiment is made up of two switching power supply units 44. The switching power supply units 44 are the second embodiment of the switching power supply unit of the present invention described above.

The two switching power supplies 44 have constants k and h set to the same value, and the output ends 22 of the power conversion units 20 are connected in parallel (operated in parallel) with equally thick and short conductors 60a and 60b, and power is supplied to a single load 18 through a load line 16 of a predetermined length connected to the connection point. The load power is the sum of the output power of the two switching power supplies 44. Furthermore, the Vm line external connection terminals 50 are interconnected.

The two switching power supply units 44 intentionally differ in the designated value Vfs of the load end voltage Vf so that the load end voltage Vf will be different when operated independently. Therefore, of the two switching power supply units 44, the one with the lowest designated value Vfs and the lowest provisional target voltage Vmx when operated independently is designated as the master power supply 44(M), and the other (with the designated value Vfs set to a sufficiently high value and the provisional target voltage Vmx when operated independently) is designated as the slave power supply 44(S) to distinguish them.

In the master power supply 44(M), the input terminal of the load end voltage detection unit 26 is connected to the load end 36 via the sensing line 38, and the load end voltage detection unit 26 is configured to output a load end detection voltage Vfk = k·Vf. On the other hand, in the slave power supply 44(S), the input terminal of the load end voltage detection unit 26 is open, and the load end voltage detection unit 26 is configured to output zero volts regardless of the value of the load end voltage Vf. Therefore, the temporary target voltage information creation unit 46 of the slave power supply 44(S) always creates temporary target voltage information J(Vmx) in the second information creation mode.

As described above, the specified value Vfs of the slave power supply 44(S) is set to a value sufficiently higher than the specified value Vfs of the master power supply 44(M). Therefore, when the master power supply 44(M) is operating normally (when the sensing line 38 is correctly connected and processing in the first information creation mode is being performed), the temporary target voltage Vmx of the master power supply 44(M) will always be lower than the temporary target voltage Vmx of the slave power supply 44(S).

Next, the operation of the target voltage generation units 48 of the master power supply 44(M) and slave power supply 44(S) will be explained based on specific numerical examples. Figure 14 shows a situation in which a tentative target voltage Vmx = 5V is input to the Vm control unit 56 with constant h = 1 for the master power supply 44(M), and a tentative target voltage Vmx = 7V is input to the Vm control unit 56 with constant h = 1 for the slave power supply 44(S).

The master power supply 44(M) is controlled by its own Vm control unit 56 to a target voltage Vm = Vmx/h = 5V. Meanwhile, if the slave power supply 44(S) were operating alone, its own Vm control unit 56 would control the target voltage Vm = Vmx/h = 7V. However, because the Vm line 50a is connected to the Vm line 50a of the master power supply 44(M) via the Vm line external connection terminal 50, the target voltage Vm is maintained at 5V. Therefore, the Vm control unit 56 of the slave power supply 44(S) is held in an uncontrollable state, with its operation of drawing current from the Vm line 50a suspended.

In Figure 14, if the target voltage Vm of the master power supply 44(M) is Vm(M), the target voltage Vm of the slave power supply 44(S) will also be Vm(M). Therefore, the output end voltage Vo of the master power supply 44(M) and the slave power supply 44(S) will be the same value, and the load end voltage Vf will also be the same value, so that the load power will be shared almost equally.

As described above, the power supply system 58 controls the target voltage Vm of one of the two switching power supply units 44 (the master power supply 44(M)) while performing feedforward remote sensing, making it possible to meet requirements such as simultaneous startup of the two switching power supply units 44, equalization of the load power burden, and easy setting changes to the load end voltage Vf. Furthermore, even if the sensing line 38 of the master power supply 44(M) suddenly becomes disconnected (for example, due to a wire breakage), the power supply to the load 18 can continue while ensuring the safety of the load 18 and each power conversion unit 20.

Note that while the power supply system 58 described above is configured to operate two switching power supply units 44 in parallel, it may also be configured to operate three or more switching power supply units 44 in parallel. When operating three or more units in parallel, only one unit will be the master power supply 44(M) and the others will all be slave power supplies 44(S), achieving the same effects as when two units are operated.

<<Other embodiments, etc.>>
The switching power supply device and power supply system of the present invention are not limited to the above-described embodiment and modifications. For example, when configuring power supply system 58, temporary target voltage information generator 46 of switching power supply device 44 may be replaced with temporary target voltage information generators 46(1) and 46(2) of the modifications, and similar effects can be obtained.

Furthermore, in the description of the power supply system 58 above, it was stated that "the output terminals 22 of the power conversion units 20 are connected in parallel (operated in parallel) with equally thick and short conductors 60a, 60b, and power is supplied to a single load 18 through a load line 16 of a predetermined length connected to the connection point." However, if circumstances prevent the conductors 60a, 60b from being sufficiently thick and short, there is a possibility that the balance of the output currents Io of the two switching power supplies 44 (balance of load power burden) will be slightly disrupted. Therefore, if more precise balancing is desired, it is advisable to apply the current balance adjustment circuit technology described in Figure 1 of Japanese Utility Model Laid-Open Publication No. 63-135406, for example.

This current balance adjustment circuit technology involves providing each power supply with a current detection circuit that detects the output current Io, interconnecting the outputs of these circuits, generating a voltage (correction voltage) of a polarity corresponding to the direction and magnitude of the unbalanced current flowing between the current detection circuits, and biasing the input voltage of the comparator. When applied to the present invention, for example, a similar current detection circuit could be provided inside each switching power supply 44, and a circuit could be added between the Vm line 50a and the control unit 34 that adds the correction voltage to the target voltage Vm generated on the Vm line 50a and inputs the result to the control unit 34. Alternatively, if conditions are met, a circuit could be added between the output terminal voltage detection unit 24 and the control unit 34 that adds the correction voltage to the output terminal detection voltage Vok and inputs the result to the control unit 34.

10, 44 Switching power supply device 12 Input terminal 16 Load line 18 Load 20 Power conversion unit 22 Output terminal 24 Output terminal voltage detection unit 26 Load terminal voltage detection unit 28 Specified voltage information creation unit 30, 30(1), 30(2), 30(3) Target voltage information creation unit 32, 48 Target voltage generation unit 32a Pulse width modulation unit 32b Low pass filter 34 Control unit 36 Load terminal 38 Sensing line 44(M) Master power supply 44(S) Slave power supplies 46, 46(1), 46(2) Temporary target voltage information creation unit 50 Vm line external connection terminal 50a Vm line 52 Temporary target voltage generation unit 52a Pulse width modulation unit 52b Low pass filter 54 Pull-up circuit 56 Vm control unit 58 Power supply system
GS external command
h positive constant
Io output current
J(Vsi) specified voltage information
J(Vm) Target voltage information
J(Vmx) Temporary target voltage information
k positive constant
Vi input voltage
Vf Load voltage
Vfk Load end detection voltage
Vfs Load voltage specification
Vg drive pulse
Vm target voltage
Vmx temporary target voltage
Vo Output terminal voltage
Vok Output terminal detection voltage
Vsi specified voltage

Claims (14)

a power conversion unit that converts a DC or AC input voltage supplied to an input terminal into a DC voltage by a switching operation of a main switching element and supplies the power to a load through a load line of a predetermined length;
an output terminal voltage detection unit that detects an output terminal voltage Vo generated at the output terminal of the power conversion unit and outputs a corresponding analog output terminal detection voltage Vok=k·Vo (k is a positive constant);
a load end voltage detection unit that detects a load end voltage Vf generated at the load end of the load line and outputs a corresponding analog load end detection voltage Vfk=k·Vf;
a designated voltage information generating unit that receives a designated value Vfs of the load end voltage Vf and generates designated voltage information J(Vsi) indicating a corresponding designated voltage Vsi=k·Vfs;
a target voltage information generating unit that performs digital calculation processing based on the output end detected voltage Vok, the load end detected voltage Vfk, and the specified voltage information J(Vsi) to generate target voltage information J(Vm) indicating a target voltage Vm=Vsi+Vok−Vfk;
a target voltage generation unit that generates an analog target voltage Vm based on the target voltage information J(Vm);
a control unit that determines an on-time and an off-time of the main switching element so that the output terminal detected voltage Vok and the target voltage Vm are equal, generates a drive pulse so that the main switching element is turned on and off during the on-time and off-time, and outputs the drive pulse to the main switching element. The switching power supply device of claim 1, wherein the target voltage generation unit is composed of a pulse width modulation unit that outputs a square wave voltage whose duty is set based on the target voltage information J(Vm), and a low-pass filter that smooths the square wave voltage to generate the target voltage Vm. The switching power supply device of claim 1, wherein the target voltage information creation unit performs processing in a first information creation mode to create the target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk when Vok - Vfk < Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create the target voltage information J(Vm) such that Vm = Vsi + Vth when Vok - Vf ≥ Vth. The switching power supply device of claim 1, wherein the target voltage information creation unit performs processing in a first information creation mode to create the target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk when Vok - Vfk < Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create the target voltage information J(Vm) such that Vm = Vsi when Vok - Vfk ≥ Vth. The switching power supply device of claim 1, wherein the target voltage information creation unit performs processing in a first information creation mode to create the target voltage information J(Vm) such that Vm = Vsi + Vok - Vfk when Vfk > Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create the target voltage information J(Vm) such that Vm = Vsi when Vfk ≤ Vth, regardless of the value of Vok - Vfk. A switching power supply device according to any one of claims 1 to 5, wherein the specified voltage information creation unit is configured to allow the specified value Vfs of the load end voltage Vf to be changed externally. a power conversion unit that converts a DC or AC input voltage supplied to an input terminal into a DC voltage by a switching operation of a main switching element and supplies the power to a load through a load line of a predetermined length;
an output terminal voltage detection unit that detects an output terminal voltage Vo generated at the output terminal of the power conversion unit and outputs a corresponding analog output terminal detection voltage Vok=k·Vo (k is a positive constant);
a load end voltage detection unit that detects a load end voltage Vf generated at the load end of the load line and outputs a corresponding analog load end detection voltage Vfk=k·Vf;
a designated voltage information generating unit that receives a designated value Vfs of the load end voltage Vf and generates designated voltage information J(Vsi) indicating a corresponding designated voltage Vsi=k·Vfs;
a temporary target voltage information generating unit that performs digital calculation processing based on the output end detected voltage Vok, the load end detected voltage Vfk, and the specified voltage information J(Vsi) to generate temporary target voltage information J(Vmx) indicating a temporary target voltage Vmx=h·(Vsi+Vok−Vfk) (h is a positive constant);
a target voltage generating unit that generates an analog target voltage Vm=Vmx/h based on the temporary target voltage information J(Vmx);
a control unit that determines an on-time and an off-time of the main switching element so that the output terminal detected voltage Vok is equal to the target voltage Vm, generates a drive pulse so that the main switching element is turned on and off during the on-time and off-time, and outputs the drive pulse to the main switching element;
a Vm line external connection terminal that enables a Vm line, which is an output line of the target voltage generation unit, to be connected to an external device;
the target voltage generation unit comprises a temporary target voltage generation unit that generates an analog temporary target voltage Vmx based on the temporary target voltage information J(Vmx) created by the temporary target voltage information creation unit; a pull-up circuit that pulls up the Vm line to a positive voltage; and a Vm control unit that has a current-drawing output stage and draws current from the Vm line when Vm > Vmx/h and stops drawing current from the Vm line when Vm ≦ Vmsx/h, thereby controlling the target voltage Vm to be a value Vmx/h that corresponds to the temporary target voltage Vmx. The switching power supply device of claim 7, wherein the temporary target voltage generation unit comprises a pulse width modulation unit that outputs a square wave voltage whose duty is set based on the temporary target voltage information J(Vmx), and a low-pass filter that smooths the square wave voltage to generate the temporary target voltage Vmx. A switching power supply device according to claim 7 or 8, wherein the specified voltage information creation unit is configured to allow the specified value Vfs of the load end voltage Vf to be changed externally. The switching power supply device of claim 7, wherein the temporary target voltage information creation unit performs processing in a first information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h (Vsi + Vok - Vfk) in the range of Vok - Vfk < Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h (Vsi + Vth) in the range of Vok - Vf ≧ Vth. 8. The switching power supply device according to claim 7, wherein the temporary target voltage information creation unit performs processing in a first information creation mode to create the temporary target voltage information J(Vmx) such that Vmx=h·(Vsi+Vok−Vfk) in a range of Vok−Vfk<Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create the temporary target voltage information J(Vmx) such that Vmx=h·Vsi in a range of Vok−Vfk≧Vth. The switching power supply device of claim 7, wherein the temporary target voltage information creation unit performs processing in a first information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h·(Vsi + Vok - Vfk) in the range of Vfk > Vth (Vth is a voltage threshold), and performs processing in a second information creation mode to create the temporary target voltage information J(Vmx) such that Vmx = h·Vsi in the range of Vfk≦Vth, regardless of the value of Vok - Vfk. A switching power supply device according to any one of claims 10 to 12, wherein the specified voltage information creation unit is configured to allow the specified value Vfs of the load end voltage Vf to be changed externally. A power supply system using a plurality of switching power supply devices according to claim 13,
In each of the switching power supply devices, the output ends of the power conversion units are connected in parallel with each other, the Vm line external connection terminals are connected with each other, the constant k is set to a uniform value, and the constant h is set to a uniform value;
When one of the switching power supply devices having the lowest designated value Vfs of the load end voltage Vf is designated as a master power supply and the others are designated as slave power supplies,
the load end voltage detection unit of the master power supply has an input end connected to the load end, detects the load end voltage Vf, and outputs the load end detection voltage Vfk;
the input terminal of the load end voltage detection unit of the slave power supply is open and outputs zero volts regardless of the value of the load end voltage Vf, which causes the temporary target voltage information creation unit of the slave power supply to create the temporary target voltage information J(Vmx) in the second information creation mode,
a target voltage Vm(M) is generated on the Vm line of the master power supply, the target voltage Vm being generated by the target voltage generation unit of the master power supply itself, and the target voltage Vm(M) input via the external connection terminal of the Vm line of the slave power supply itself is generated on the Vm line of the slave power supply itself;
a power supply system characterized in that the control units of the master power supply and the slave power supply generate the drive pulses so as to reduce the difference between the target voltage Vm(M) generated on the Vm line of the master power supply and the output terminal detection voltage Vok of the slave power supply.