JP3480554B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply that stabilizes an output voltage by using a pulse width control method, and more particularly to improvement of an abnormality processing method of feedback voltage control on the primary side.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a conventional switching power supply. In the figure, a DC voltage VIN is applied to the primary winding 21 of the transformer and is turned on / off by a switching element 35 such as an FET. Then, since the primary current a flows in a pulse shape, a switching current is induced in the secondary winding 22, and this is converted into a direct current by the rectifier circuit composed of the diode 51 and the capacitor 52 and supplied to the load circuit 61.

FIG. 1 is a diagram showing the case where power is supplied to two load circuits, and the diode 53, the capacitor 54 and the load circuit 62 have the same construction as described above.

In the switching power supply shown in FIG. 3, the voltage induced in the transformer 20 is detected by the winding 24 by turning on / off the primary current a, and this is fed back to the control IC 10 and sent to the switching element 35. The DC voltage supplied to the secondary side is stabilized by controlling the duty ratio of the ON / OFF signal VO.

The switching current induced in the winding 24 by turning on / off the primary current a flowing in the primary winding 21 is converted into a direct current by a rectifying circuit composed of a diode 31 and a capacitor 32, and a feedback current IF Is input to the feedback terminal FB of the control IC 10 via the resistors 12 and 13. At this time, the feedback current IF is the resistance 12 and the resistance 13.
Since the voltage is converted by, the feedback voltage is input to the feedback terminal FB of the control IC 10.

The control IC 10 has a feedback terminal F.
The feedback voltage input to B is compared with a preset setting voltage VS to obtain an error voltage, the duty ratio of the on / off signal VO is adjusted to reduce the error voltage, and switching is performed via the resistor 11. Element 35
Output to the gate of.

By thus performing the feedback control on the primary side of the power supply, it becomes possible to keep the DC voltage supplied to the secondary side constant.

Further, the switching power supply shown in FIG. 3 is provided with a limit circuit for limiting the upper limit of the voltage induced in the transformer 20. The circuit for detecting the voltage rise for doing this is the Zener diode 41 and the resistor 42. This voltage limit operation will be described below.

In FIG. 3, the feedback current IF obtained by rectifying the switching current induced in the winding 24 is connected to the cathode of the Zener diode 24, and the anode is connected to the output stop signal input terminal DIS of the control IC. It is connected to one end of the resistor 42. The other end of the resistor 42 is connected to the common potential.

In the circuit having such a structure, for example, when the feedback control on the primary side of the power supply is disabled due to a circuit abnormality or the like, the control IC 10 does not apply a voltage to the feedback terminal FB, and therefore the transformer 20 is used.
The on / off signal VO is output in the direction of increasing the voltage of the.

As a result, the feedback current I
F gradually increases, and the voltage generated between the anode and the cathode of the Zener diode 41 eventually becomes the Zener voltage VZ.
When it exceeds, the Zener current IZ comes to flow in the resistor 42.

The output stop signal input terminal DI of the control IC 10 is caused by the Zener current IZ flowing through the resistor 42.
A signal voltage VDIS having a magnitude obtained by multiplying S by the resistor 42 and the Zener current IZ is applied to S.

The control IC 10 stops the output of the on / off signal VO when the signal voltage VDIS is applied to the output stop signal input terminal DIS. As a result, the primary current a does not flow and the windings 22, 23, 24 of the transformer 20
The voltage is no longer induced.

Then, the switching current IF decreases and the Zener current IZ also stops flowing, so that the signal voltage VDIS becomes "0V" and the output of the on / off signal VO restarts. As a result, the primary current a also flows, and a voltage is generated in the windings 22, 23, 24 of the transformer 20.

By repeating the above operation, when the feedback control of the power supply circuit is disabled, the state in which the primary current a flows or does not flow continues, but the diode on the secondary side does not flow. Since the smoothing circuit composed of 51 and 53 and capacitors 52 and 54 has a sufficiently large time constant, the DC voltage supplied to the secondary side has a voltage fluctuation in the vicinity of the Zener voltage VZ, although there is some voltage fluctuation. It is possible to continue the supply.

[0016]

However, in the conventional switching power supply, when the feedback control on the primary side of the power supply is disabled, the supply voltage to the secondary side is near the Zener voltage VZ which is the output voltage upper limit value. To be stable
Power consumption in the load circuit on the secondary side becomes excessive, which may result in burnout of the element due to heat generation and accompanying accidents such as electric shock and burns.

In the conventional switching power supply, when the feedback control on the primary side of the power supply becomes impossible, there is a method of stopping the switching operation to stop the supply voltage to the secondary side. Since the power supply to all the load circuits on the secondary side is stopped, there is a problem in that the power supply to the important circuits such as the alarm output circuit is cut off together with the load circuits with large power consumption. It was

The present invention solves the above problems by detecting a circuit abnormality that has occurred on the primary side of a power supply by detecting a voltage fluctuation appearing in a DC voltage on the secondary side, and detecting a plurality of loads provided on the secondary side. An object of the present invention is to provide a switching power supply capable of individually controlling circuits.

[0019]

In order to achieve such an object, the invention according to claim 1 limits the upper limit of the voltage induced in the transformer in the switching power supply.
However, if the control becomes impossible, the primary current will be intermittent.
Limit circuit that keeps flowing state and the limit
An abnormality detecting circuit for detecting the large voltage variation based on circuit, the abnormality detection circuit load circuit control circuit capable of individually controlling the plurality of load circuits provided on the secondary side by the generated abnormal signal by It is characterized by having.

With this, it becomes possible to detect the abnormality of the circuit generated on the primary side of the power supply by the abnormality detection circuit on the secondary side which is completely insulated, and a plurality of loads provided on the secondary side. It is possible to control the circuits individually.

According to a second aspect of the invention, in the first aspect of the invention, the abnormality detection circuit inputs the switching current generated in the secondary winding to a rectifying / smoothing circuit having a small time constant, It is characterized in that an abnormal signal is generated by inputting the DC voltage obtained by this to a comparator.

This makes it possible to detect an abnormal signal on the primary side with a circuit having a simple structure.

According to a third aspect of the present invention, in the first aspect of the present invention, the load circuit control circuit is equipped with a CPU and is configured to be programmable.

This makes it possible to control a plurality of load circuits provided on the secondary side in various patterns due to the occurrence of an abnormality on the primary side of the power supply.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the load circuit control circuit is equipped with a CPU, and when a circuit abnormality that occurs on the primary side of the power supply is detected, the secondary It is characterized in that the plurality of load circuits provided on the side are programmed so as to sequentially shut off from the one having the largest power consumption.

As a result, it becomes possible to immediately shut off the load circuit with large power consumption after detecting the occurrence of an abnormality on the primary side of the power supply.

[0027]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a switching power supply according to the present invention.

In the figure, the circuit on the primary side of the power supply and the load circuits 61 and 62 on the secondary side have the same configurations as those of FIG. 3 described in the conventional example, and therefore the description thereof is omitted here.

In FIG. 1, the terminal 22 of the secondary winding 22 is
The cathode of the diode 55 is connected to b, and the anode is connected to the input terminal of the comparator 57 and one end of the capacitor 56. The other end of the capacitor 56 is connected to the terminal 22a of the secondary winding 22.

The output e of the comparator is the CPU 58.
Control output f of the CPU 58 is input to the load circuit 61,
62 is connected to the control signal input terminal. The comparator 57 can set the comparison level CL for comparison with the input signal level.

In the circuit having such a configuration, the operation when the feedback control is disabled on the primary side of the power supply will be described.
This will be described with reference to the operation waveform diagram shown in FIG.

When the feedback control is disabled on the primary side of the power supply, the control IC 1 is operated by the operation of the Zener diode 41 and the resistor 42 described in FIG.
A state in which the signal voltage VDIS is generated at the output stop signal input terminal DIS of 0 (hereinafter referred to as a Hi state) and a state in which the signal voltage VDIS is not generated (hereinafter referred to as a Lo state) are repeated.

As a result, the waveform shown in FIG. 2 appears in each part of the switching power supply according to the present invention.

In the figure, a region 81 is a state in which the switching element 35 repeats the on / off operation, and a region 82 is a state in which the switching element 35 stops the on / off operation.

At this time, the primary current a flowing through the resistor 36 is
As shown in the figure, a pulse current flows in a rectangular wave shape, but the direct current b generated on the secondary side by this passes through a smoothing circuit composed of a diode 51 and a capacitor 52 having a sufficient time constant. It appears as a secondary side DC voltage b having a gentle voltage fluctuation as shown in the figure.

Similarly, in the smoothing circuit constituted by the diode 53 and the capacitor 54, the secondary side DC voltage c having a gentle voltage fluctuation as shown in the figure is generated.

Similarly, a DC voltage d is also generated in the smoothing circuit composed of the diode 55 and the capacitor 56. The time constant of this smoothing circuit is the load circuit 61,
Since it is set to be much smaller than the two smoothing circuits connected to 62, a secondary side DC voltage d having a large voltage fluctuation as shown in the figure is generated.

2 with a large voltage fluctuation generated here
The secondary DC voltage d is input to the comparator 57, where it is compared with the comparator level CL and the power fail signal e is input to the CPU 58.

The CPU 58 recognizes the abnormality on the primary side of the power supply by the power fail signal e inputted here, and according to the preprogrammed operation, the load circuit 6
The control signal f is output to 1 and 62, and the power supply to the load circuit with large power consumption is cut off.

That is, when the voltage feedback control is disabled on the primary side of the power source, the output current limit operation by the Zener diode or the like keeps the primary current a flowing intermittently, so that the secondary winding is wound. The induced switching current fluctuates. This switching current is input to the rectifying / smoothing circuit having a small time constant, and is output as a DC voltage d including a large voltage fluctuation. Comparator 57
Compares the DC voltage d with a preset comparator level CL to detect the occurrence of voltage fluctuation, and detects a power fail signal as a power supply abnormality signal on the primary side.
Output e.

By detecting the ON state of the power fail signal e, the CPU 58 can individually shut off the load circuits on the secondary side according to a preprogrammed operation program at the time of power supply abnormality.

The above description merely shows specific preferred embodiments for the purpose of describing and exemplifying the present invention. Therefore, the present invention is not limited to the above-mentioned embodiment, and many modifications are made without departing from the essence thereof.
It also includes deformation.

[0043]

As is apparent from the above description,
The present invention has the following effects. In the invention according to claim 1, in the switching power supply, the transformer
The upper limit of the voltage induced in the
If the primary current continues to flow intermittently,
It is possible to individually control a mitt circuit, an abnormality detection circuit that detects a large voltage fluctuation based on the limit circuit, and a plurality of load circuits provided on the secondary side by an abnormality signal generated by the abnormality detection circuit. By providing such a load circuit control circuit , it becomes possible to detect a circuit abnormality that has occurred on the primary side of the power supply by means of a completely insulated secondary side abnormality detection circuit. Further, it becomes possible to shut off the load circuit that consumes a large amount of power at the same time as the occurrence of an abnormality, and to continue the operation of only the important load circuit such as the alarm output circuit.

According to the invention described in claim 2, in the invention described in claim 1, since the abnormality detection circuit is implemented by a simple circuit configuration composed of a rectifying and smoothing circuit having a small time constant and a comparator, space saving is achieved. It is possible to produce at low cost.

In the invention described in claim 3, in the invention described in claim 1, the load circuit control circuit is a CP
Since the U is installed and is configured to be programmable, it is possible to provide a highly flexible switching power supply that can be installed in various devices.

In the invention described in claim 4, in the invention described in claim 1, the load circuit control circuit is a CP.
When U is installed and a circuit abnormality that occurs on the primary side of the power supply is detected, it is programmed to sequentially shut down the load circuit with the largest power consumption from among the multiple load circuits provided on the secondary side. It is possible to prevent burns, electric shocks, etc. due to increased power consumption that tends to occur during power failure.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a switching power supply according to the present invention.

FIG. 2 is a diagram showing a signal waveform of the switching power supply according to the present invention.

FIG. 3 is a configuration diagram showing an example of a conventional switching power supply.

[Explanation of symbols]

10 Control IC 11 12 13 36 37 37 42 Resistance 20 transformers 21 22 23 24 winding 31 51 53 55 Diode 32 52 54 56 capacitors 41 Zener diode 25 switching elements 57 Comparator 58 CPU 61 62 Load circuit

Claims (4)

(57) [Claims] 1. A smoothing for supplying a DC voltage to a load circuit by rectifying and smoothing a switching current induced in a secondary winding of the transformer by turning on and off a current flowing in a primary winding of the transformer by a switching element. The switching current induced in the circuit and the primary side of the transformer is rectified and smoothed and taken out as a feedback voltage, and the duty ratio of the on / off signal sent to the switching element is controlled by monitoring the feedback voltage to control the secondary side. In a switching power supply having a control circuit that constantly controls a DC voltage supplied to the transformer, the upper limit of the voltage induced in the transformer is limited, and the control
If it becomes impossible to change the state of the primary current flowing intermittently,
A limit circuit to be continued, an abnormality detection circuit that detects a large voltage fluctuation based on the limit circuit, and a plurality of load circuits provided on the secondary side are individually controlled by an abnormality signal generated by the abnormality detection circuit. switching power supply being characterized in that a possible load circuit control circuits. 2. The abnormality detection circuit inputs the switching current generated in the secondary winding to a rectifying / smoothing circuit having a small time constant, and inputs a DC voltage obtained thereby to a comparator to output an abnormality signal. The switching power supply according to claim 1, wherein the switching power supply is configured to generate. 3. The switching power supply according to claim 1, wherein the load circuit control circuit is equipped with a CPU and is configured to be programmable. 4. The load circuit control circuit is provided with a CPU, and when a circuit abnormality occurring on the primary side of the power supply is detected,
2. The switching power supply according to claim 1, wherein the switching power supply is programmed so as to sequentially cut off a load circuit having a large power consumption from among a plurality of load circuits provided on the secondary side.