JP7519022B2 - Device - Google Patents

Description

The present invention relates to a device equipped with a switching power supply.

Conventionally, switching power supplies use burst switching control, which involves repeatedly temporarily stopping the switching operation of a switching element and then restarting the switching operation.

The switching power supply device of JP 2004-88959 A has a signal level judgment circuit and a switching control circuit on the primary side of the transformer, and an output voltage detection circuit on the secondary side of the transformer. When the main output voltage detected by the output voltage detection circuit rises, the signal level judgment circuit stops the supply of operating power to the switching control circuit, and when the output voltage detected by the output voltage detection circuit falls, the signal level judgment circuit resumes the supply of operating power to the switching control circuit, thereby reducing power consumption.

JP 2004-88959 A

However, in conventional switching power supplies, although the switching control circuit provided on the primary side of the transformer can be stopped, the signal level determination circuit provided on the primary side of the transformer cannot be stopped, and the output voltage detection circuit provided on the secondary side of the transformer cannot be stopped either.

The object of the present invention is to provide a device that can stop the detection operation of the detection signal by the primary side control unit and the switching control of the switching element when temporarily stopping the switching operation during burst switching control.

In order to solve the above problems, a device according to one aspect of the present invention includes a transformer having a drive unit, a primary winding, and a secondary winding connected to the drive unit, and outputting an output voltage from the secondary winding to the drive unit, a switching element connected to the primary winding, a detection signal output unit provided on the secondary side of the transformer, detecting the output voltage and outputting a detection signal indicating whether the output voltage is equal to or greater than a predetermined value, a primary side control unit provided on the primary side of the transformer, performing switching control of the switching element in response to the detection signal, and a control unit having a voltage detection unit that drives based on the input output voltage and detects the output voltage, and the switching element is switched. In the case of burst switching control, in which the switching operation is repeatedly stopped and restarted, the control unit outputs a stop signal to the primary side control unit when the voltage detection unit detects that the output voltage exceeds a first voltage, and then outputs a resume signal to the primary side control unit when the voltage detection unit detects that the output voltage has dropped below a second voltage that is lower than the first voltage. The primary side control unit is configured to stop the detection operation of the detection signal and the switching control of the switching element in response to receiving the stop signal, and then resume the switching control of the switching element in response to receiving the resume signal.

According to one aspect of the present invention, when the switching operation during burst switching control is temporarily stopped, it is possible to realize a device that can stop the detection operation of the detection signal by the primary side control unit and the switching control of the switching element.

1 is a schematic diagram showing a configuration of an apparatus according to a first embodiment of the present invention. 4 is a time chart showing the operation of the device according to the first embodiment of the present invention.

[Embodiment 1]
Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS.

(Overall configuration of the device)
1 is a schematic diagram showing the configuration of an apparatus 10 according to embodiment 1. The apparatus 10 is composed of a low-voltage power supply 100, a drive unit 20 driven by power supplied from the low-voltage power supply 100, and a control unit 220 driven by power supplied from the low-voltage power supply 100 and controlling the drive unit 20. The apparatus 10 is an apparatus equipped with a flyback type switching power supply that operates by receiving AC power from an external AC power supply 90. The drive unit 20 is an image forming unit, and the apparatus 10 is an image forming apparatus, but is not limited thereto.

(Low voltage power supply configuration)
The low-voltage power supply 100 includes a primary side rectifying and smoothing circuit 110, a transformer 120, a switching element 130, a primary side DC power supply generating circuit 131, a primary side control unit 132, a feedback circuit 133, an enable signal transmission circuit 134, a secondary side rectifying and smoothing circuit 140, a detection signal output unit 150, and an overcurrent protection circuit 160.

The transformer 120 is provided with a main winding 121 and a secondary winding 124. The main winding 121 is composed of a primary winding 122 and a secondary winding 123. The primary side rectifying and smoothing circuit 110 is a circuit that smoothes the power from the AC power source 90 into a voltage waveform close to DC and outputs it. The output of the primary side rectifying and smoothing circuit 110 is introduced into the primary winding 122.

The switching element 130 is connected in series to the primary winding 122 of the transformer 120. When the switching element 130 is conductive, a current flows from the primary side rectifying and smoothing circuit 110 to the primary winding 122, and when it is cut off, no current flows. The switching element 130 is a voltage-driven semiconductor element whose on/off is controlled by a gate voltage. The switching element 130 can be a MOS-FET (Metal-Oxide Semiconductor Field Effect Transistor) or another FET.

The primary side DC power generation circuit 131 is a circuit that outputs DC power connected to the secondary winding 124 of the transformer 120. The primary side DC power generation circuit 131 is provided on the primary side of the transformer 120. When the switching element 130 performs a switching operation, AC power is excited in the secondary winding 124, and the primary side DC power generation circuit 131 smoothes the voltage waveform to a voltage close to DC and supplies DC power to the primary side control unit 132. The primary side control unit 132 is driven by a drive voltage from the primary side of the transformer 120. The primary side DC power generation circuit 131 has an element that can temporarily store energy, such as a capacitor or inductor, and the supply of power is maintained for a certain period of time even if the switching operation stops.

The primary side control unit 132 is a circuit that controls the switching element 130. The primary side control unit 132 applies a pulse voltage of the required frequency and duty to the gate of the switching element 130, and performs switching control in the device 10.

The secondary side rectifying and smoothing circuit 140 is connected to the secondary winding 123 of the transformer 120. When the switching element 130 performs a switching operation, AC power is excited in the secondary winding 123, and the secondary side rectifying and smoothing circuit 140 smooths the voltage waveform to a voltage close to DC and outputs it. The secondary side rectifying and smoothing circuit 140 has an element that temporarily stores energy, such as a capacitor or inductor, and even if the switching operation stops, the supply of power is maintained for a certain period of time, although the output voltage Vo gradually decreases.

The detection signal output unit 150 is a circuit that detects the output voltage of the secondary side rectifying and smoothing circuit 140, which is also the output voltage Vo of the low-voltage power supply 100 itself. During normal control operation, the device 10 operates so that the output voltage Vo becomes the target voltage Vt (predetermined value). To this end, the detection signal output unit 150 monitors the output voltage Vo and feeds back to the primary side control unit 132 a detection signal Ss that can indicate at least whether the output voltage Vo is equal to or greater than the target voltage Vt.

The primary side control unit 132 has an internal pulse voltage generation circuit and a monitoring circuit that monitors the reception of the detection signal Ss. During normal control operation, the primary side control unit 132 controls the frequency and duty of the pulse voltage according to the detection signal Ss, and performs switching control so that the output voltage Vo becomes the target voltage Vt. This normal control operation is the normal operation of a switching power supply that is also performed in conventional technology.

The feedback circuit 133 is a photocoupler that transmits the detection signal Ss while ensuring insulation between the detection signal output unit 150 connected to the secondary winding 123 side of the transformer 120 and the primary side control unit 132 connected to the primary winding 122 side.

When the photocoupler transmits the detection signal Ss, the light emission intensity of the photodiode can indicate whether the output voltage Vo is equal to or greater than the target voltage Vt. This method of generating the detection signal Ss is similar to the conventional technology described in Patent Document 1. However, it is preferable to configure the photodiode to be turned on or off to indicate whether the output voltage Vo is equal to or greater than the target voltage Vt.

In the former case, the photodiode emits light whether the output voltage Vo is greater than or equal to the target voltage Vt or less, whereas in the latter case, it does not emit light when the output voltage Vo is less than the target voltage Vt. The photodiode does not emit light when the voltage applied to the photodiode is less than the threshold voltage of the diode characteristics. In this case, almost no current flows through the photodiode, and power consumption of the photodiode and the circuit that passes current through the photodiode is reduced. Furthermore, as described below, even in burst switching control operation in which the output voltage Vo remains below the target voltage Vt, the photodiode does not emit light, and power consumption is suppressed.

The enable signal transmission circuit 134 is a circuit for transmitting an enable signal Sb (Enable signal) described later while ensuring insulation between a control unit 220 (described later) connected to the secondary winding 123 side of the transformer 120 and a primary side control unit 132 (described later) connected to the primary winding 122 side. The enable signal transmission circuit 134 is composed of a photocoupler.

The overcurrent protection circuit 160 is connected to the secondary side rectifying and smoothing circuit 140. The overcurrent protection circuit 160 monitors the output of the low voltage power supply 100 and prevents an overcurrent from flowing toward the drive unit 20. The overcurrent protection circuit 160 achieves this function by bypassing the current when an excessive current is about to flow to the output of the low voltage power supply 100. The overcurrent protection circuit 160 operates by consuming a portion of the power output by the secondary side rectifying and smoothing circuit 140.

In addition, since the voltages on the input and output sides of the overcurrent protection circuit 160 are substantially the same, the output voltage of the secondary side rectifying and smoothing circuit 140 is also described in the specification as being the same as the output voltage Vo.

(Configuration of the drive unit)
The drive unit 20 is supplied with output power, which is DC power, from the low-voltage power supply 100. The transformer 120 outputs an output voltage from a secondary winding 123 to the drive unit 20.

The drive unit 20 is an image forming unit that operates by receiving DC power from the low-voltage power supply 100. The drive unit 20 that operates as an image forming unit forms a toner image on a sheet by a well-known electrophotographic method, and is composed of a process unit, a fixing device, a conveying unit that conveys the sheet, etc.

(Configuration of DC-DC Converter Circuit)
The device 10 includes a DC-DC converter circuit 210 in addition to the low-voltage power supply 100 and the drive unit 20. The DC-DC converter circuit 210 is a circuit that is branched and connected to the output of the low-voltage power supply 100 to the drive unit 20, and is used to supply DC power to the control unit 220. The control unit 220 is driven based on the input output voltage. The output voltage Vo of the low-voltage power supply 100 is about 6 V, which is a relatively high voltage, when the image forming unit, which is the drive unit 20, is not performing image formation. The voltage supplied to the control unit 220 is about 3.3 V, which is a relatively low voltage. The DC-DC converter circuit 210 supplies DC power from the low-voltage power supply 100 to the control unit 220 while converting the voltage.

(Configuration of the control unit)
The control unit 220 is provided with a voltage detection unit 221 that indirectly detects the output voltage Vo by monitoring the voltage supplied to the control unit 220. The control unit 220 is an ASIC (Application Specific Integrated Circuit) and has a CPU (Central Processing Unit), a RAM (Random Access Memory) (not shown), and a ROM (Read Only Memory) (not shown). The ROM stores various control programs, various settings, initial values, etc. for controlling the image forming unit, which is the driving unit 20. The RAM is used as a working area from which the various control programs are read out, or as a storage area for temporarily storing image data. The control unit 220 reads out various programs from the ROM to control the image forming unit, which is the driving unit 20.

When the control unit 220 controls the drive unit 20 in the normal control operation mode, the control unit 220 does not operate the voltage detection unit 221. The control unit 220 operates the voltage detection unit 221 in the power saving mode in which the drive unit 20 is not operated. During burst switching control operation in the power saving mode, the control unit 220 operates the voltage detection unit 221, generates an enable signal Sb based on the result, and transmits it to the primary side control unit 132 via the enable signal transmission circuit 134.

(Characteristic operation of the device)
The device 10 according to the first embodiment performs a characteristic operation during burst switching control operation.

When the primary side control unit 132 receives a stop signal as an enable signal Sb from the control unit 220, it stops generating the pulse voltage and stops the switching operation. It cuts off or reduces the power supply to the pulse voltage generation circuit and the detection signal Ss monitoring circuit inside the primary side control unit 132, thereby reducing power consumption. Even while the switching operation is stopped, the primary side control unit 132 operates the partial circuit that monitors the enable signal Sb. Therefore, the necessary power supply to the partial circuit is maintained. When the primary side control unit 132 receives a resume signal as an enable signal Sb from the control unit 220, it resumes the power supply to the internal pulse voltage generation circuit and the detection signal Ss monitoring circuit, and resumes the switching operation.

The control unit 220 outputs a stop signal as an enable signal Sb when the burst switching control operation starts. The control unit 220 operates the voltage detection unit 221 during the burst switching control operation. The control unit 220 outputs a stop signal as an enable signal Sb to the primary side control unit 132 when the voltage detection unit 221 detects that the output voltage Vo exceeds a first voltage V1, which is a predetermined voltage. In addition, the control unit 220 outputs a resume signal as an enable signal Sb to the primary side control unit 132 when the voltage detection unit 221 detects that the output voltage Vo drops below a second voltage V2, which is a predetermined voltage. The second voltage V2 is a voltage smaller than the first voltage V1. Here, the enable signal Sb is a non-signal except when the stop signal or resume signal is output.

Figure 2 is a time chart for explaining the operation of the device 10. Figure 2 shows the output voltage Vo and power consumption Pc from when the device 10 transitions from normal control operation to burst switching control operation and then returns to normal control operation. Power consumption Pc is the power consumed internally by the low-voltage power supply 100, and Figure 2 shows an overview of this transition.

Initially, in normal control operation, as described above, the primary side control unit 132 controls the switching of the switching element 130 based on feedback of the output voltage Vo from the detection signal output unit 150. Therefore, the output voltage Vo is maintained at the target voltage Vt.

Next, at time T1, when the burst switching control operation starts, the control unit 220 outputs a stop signal as an enable signal Sb to the primary side control unit 132. The primary side control unit 132 stops the switching control, the switching element 130 turns off, and the output voltage Vo gradually decreases. At this time, the power supply to the pulse voltage generation circuit and the detection signal Ss monitoring circuit in the primary side control unit 132 is cut off or reduced, and the power consumption Pc of the low-voltage power supply 100 decreases.

The output voltage Vo continues to decrease, and at time T2 when it falls below the second voltage V2, the voltage detection unit 221 detects this. The control unit 220 outputs a resume signal as an enable signal Sb to the primary side control unit 132. Then, power supply to the pulse voltage generation circuit and the detection signal Ss monitoring circuit in the primary side control unit 132 is resumed, and the power consumption Pc of the low-voltage power supply 100 increases. In addition, the primary side control unit 132 resumes the switching operation of the switching element 130, and the output voltage Vo gradually increases.

The output voltage Vo continues to rise, and at time T3 when it exceeds the first voltage V1, the voltage detection unit 221 detects this. The control unit 220 outputs a stop signal as an enable signal Sb to the primary side control unit 132. Since the primary side control unit 132 stops switching control, the switching element 130 remains in the off state, and the output voltage Vo gradually decreases. At this time, the power supply to the pulse voltage generation circuit and the detection signal Ss monitoring circuit in the primary side control unit 132 is cut off or reduced, and the power consumption Pc of the low-voltage power supply 100 decreases.

After this, the switching operation is repeatedly restarted at times T4, T6, and T8, and stopped at times T5 and T7.

In addition, FIG. 2 also shows the lower limit Vm of the detection signal output unit 150. The lower limit Vm of the detection signal output unit 150 is a value smaller than the target voltage Vt. In addition, the first voltage V1 is set to a value smaller than the lower limit Vm of the detection signal output unit 150.

The lower operating limit Vm is a voltage at which the photodiode of the feedback circuit 133 does not emit light. When the photodiode is below the threshold voltage, almost no current flows, and as a result, when the output voltage Vo is at the lower operating limit Vm, the power consumption of the detection signal output unit 150 and the feedback circuit 133 is very small. In addition, since the output voltage Vo operates so as not to exceed the first voltage V1 during burst switching control operation, the detection signal output unit 150 and the feedback circuit 133 in the device 10 consume almost no power during burst switching control operation.

After time T8, when the burst switching control operation is released, the output voltage Vo rises and exceeds the first voltage V1, and then exceeds the lower operating limit Vm. Then, the feedback of the output voltage Vo by the detection signal output unit 150 to the primary side control unit 132 is resumed, and the operation transitions to normal control operation in which the output voltage Vo is maintained at the target voltage Vt.

(effect)
As described above, in the device 10, when the switching operation stops during the burst switching control operation, the power supply to the circuit parts necessary for switching control in the primary side control unit 132 is cut off or reduced. Therefore, when the switching operation stops, the power consumption of the primary side control unit 132 is significantly reduced. Furthermore, in the device 10, the detection signal output unit 150 and the feedback circuit 133 consume almost no power during the burst switching control operation.

In the conventional technology of Patent Document 1, the voltage detection circuit corresponding to the detection signal output unit 150 needs to continue operating even during burst switching control operation. In addition, to achieve this, the signal level determination circuit corresponding to the monitoring circuit for the detection signal Ss in the primary side control unit 132 and the feedback circuit corresponding to the feedback circuit 133 also need to continue operating. In the device 10, since it is not necessary to operate these circuit parts, power consumption during burst switching control operation is effectively suppressed compared to the conventional technology of Patent Document 1.

On the other hand, in the device 10, it is necessary to operate the control unit 220 during burst switching control operation. However, the control unit 220 is composed of ICs manufactured using microfabrication technology, such as ASICs, microprocessors, CPUs, etc., and can operate with low power consumption. Therefore, the increase in power consumption caused by operating the control unit 220 to monitor the output voltage Vo during burst switching control operation is small.

The enable signal Sb, which is used to feed back information about the output voltage Vo during burst switching control operation, is a signal that is generated only when the switching operation changes. Since the enable signal Sb is a silent signal for most of the period, it consumes almost no power for its transmission, and the enable signal transmission circuit 134 also consumes almost no power.

In addition, in the device 10, the detection signal output unit 150 for detecting the output voltage Vo during normal control operation and the voltage detection unit 221 for detecting the output voltage Vo during burst switching control operation are separate circuits. Therefore, the magnitudes of the first voltage V1 and the second voltage V2 that determine the stop and restart of the switching operation during burst switching control operation can be set regardless of the circuit configuration of the detection signal output unit 150. Therefore, the second voltage V2 for restarting the switching operation can be significantly reduced from the target voltage Vt, and therefore the period during which the switching operation is stopped can be extended. This makes it possible to further reduce power consumption in burst switching control operation.

In the device 10, it is also preferable that the first voltage V1 is less than the lower limit voltage of the overcurrent protection circuit 160. As a result, the overcurrent protection circuit 160 cannot operate during burst switching control operation, and power consumption is eliminated. Note that since the burst switching control operation is performed in a low load state, there is no need to monitor overcurrent. This configuration can further reduce power consumption during burst switching control operation.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed. Furthermore, new technical features can be formed by combining the technical means disclosed in the embodiments.

10 Apparatus 100 Low voltage power supply 110 Primary side rectifying and smoothing circuit 120 Transformer 121 Main winding 122 Primary winding 123 Secondary winding 124 Sub-winding 130 Switching element 131 Primary side DC power supply generating circuit 132 Primary side control unit 133 Feedback circuit 134 Enable signal transmission circuit 140 Secondary side rectifying and smoothing circuit 150 Detection signal output unit 160 Overcurrent protection circuit 210 DC-DC converter circuit 220 Control unit 221 Voltage detection unit 20 Drive unit (image forming unit)
90 AC power supply Ss Detection signal Sb Enable signal Vo Output voltage Vt Target voltage V1 First voltage V2 Second voltage

Claims (3)

a transformer having a primary winding, a secondary winding, and an auxiliary winding;
A power supply voltage generating circuit connected to a secondary winding of the transformer for smoothing an AC voltage excited in the secondary winding;
A secondary side rectifying and smoothing circuit that outputs an output voltage;
A switching element connected to the primary winding;
a detection signal output unit provided on a secondary side of the transformer, the detection signal output unit detecting the output voltage and outputting a detection signal indicating whether the output voltage is equal to or greater than a predetermined value;
a primary side control unit provided on a primary side of the transformer and configured to perform switching control of the switching element in response to the detection signal;
A low voltage power supply having
a drive unit that is driven by an output voltage input from the low-voltage power supply;
a control unit for controlling the drive unit, the control unit being driven based on the output voltage input from the low-voltage power supply and having a voltage detection unit for detecting the output voltage;
In the case of performing burst switching control in which the switching element repeatedly stops and resumes a switching operation,
The control unit is
When the voltage detection unit detects that the output voltage exceeds a first voltage, a stop signal is output to the primary side control unit, and then
When the voltage detection unit detects that the output voltage has dropped below a second voltage that is lower than the first voltage, a restart signal is output to the primary side control unit;
The primary side control unit is
In response to receiving the stop signal, the detection operation of the detection signal and the switching control of the switching element are stopped, and then
The apparatus, in response to receiving the restart signal, restarts the detection operation of the detection signal and the switching control of the switching element. A feedback circuit is further provided,
The feedback circuit is a photocoupler having a photodiode and transmitting the detection signal between the detection signal output unit and the primary side control unit while ensuring insulation,
2. The apparatus of claim 1 , wherein the photodiode emits light if the output voltage is greater than or equal to the predetermined value, and the first voltage is a voltage less than the predetermined value. a primary-side DC power supply generating circuit connected to a secondary winding of the transformer, smoothing an AC voltage excited in the secondary winding and outputting a drive voltage which is a DC voltage;
Further comprising:
The primary side control unit is
Driven by the drive voltage output from the primary side DC power supply generating circuit,
The device described in claim 1 or 2, characterized in that while the detection operation of the detection signal and the switching control of the switching element are stopped in response to receiving the stop signal, the primary side control unit is supplied with a voltage required for receiving the resume signal from the drive voltage.

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