JP2018023190A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve current responsiveness when outputting a current steeply from a state where a voltage higher than an output voltage of switching power supply device itself is applied from the outside.SOLUTION: A switching power supply device 10 comprises: a power conversion part 12; a feedback control circuit 26 which outputs an error between a reference voltage of a reference voltage source 28 and an output detection voltage as a feedback signal; and a PWM control circuit 30 which compares a triangular wave signal with the feedback signal and controls a switching element 14. A switching operation monitor circuit 32 outputs a switching operation stop detection signal to the reference voltage source 28, when performing operation in parallel with the other switching power supply device, and when a voltage higher than an output voltage of its own is applied to the output of the power conversion part 12 and turning-off of the switching element 14 for a predetermined time or longer is detected. The reference voltage source 28 increases the reference voltage and suppresses deviation of the feedback signal from the triangular wave signal, thereby eliminating response delay when outputting a current steeply.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply device used in a switching power supply system that performs parallel operation.

  2. Description of the Related Art Conventionally, a switching power supply system that uses a plurality of switching power supply apparatuses connected in parallel is known.

  In the case where current is obtained from this switching power supply system, if there is variation in the output voltage setting value of each switching power supply device in the switching power supply system, the switching power supply device having a high output voltage setting value outputs a large amount of current. Thus, the output currents of the respective switching power supply devices become unbalanced.

  When the output current becomes unbalanced, there arises a problem that heat generation of the switching power supply device that outputs a large amount of current increases and the life is shortened. In a switching power supply system, a failure of the switching power supply device that constitutes the system becomes a failure of the system. Therefore, the output current of each switching power supply device that constitutes the system is balanced, and the heat generation is made uniform to equalize the life. Measures are taken to extend the life of the system (Patent Document 1).

JP 2007-143292 A JP 2008-289298 A

  By the way, since the current balance technique disclosed so far functions when the difference between the currents output from the switching power supply devices constituting the switching power supply system is a certain value or more, the switching power supply system is operated without a load. If there is, the current balance technique does not function because there is no difference in the current output by each switching power supply device.

  Then, when a large output current is suddenly extracted from the switching power supply system operating with no load, a response time delay until the output current increases occurs. Specifically, a response delay in current output occurs when an output current larger than the current value that can be output by one switching power supply device constituting the system is taken out from a switching power supply system in a no-load state.

  In general, countermeasures are taken against the poor response characteristics of the output current of the switching power supply by increasing the capacity of the capacitor on the output side of the switching power supply. As a result, current can be supplied from the capacitor on the output side of the switching power supply until the control circuit of the switching power supply responds, and the response characteristics of the switching power supply with respect to the output current can be improved. However, this measure requires a large capacitor, which leads to an increase in the size and cost of the switching power supply device.

(Operation of the switching power supply system when there is no load)
In the switching power supply system that is operated with no load, the operation of the individual switching power supply devices constituting the system will be described.

  Prior to describing the operation of the switching power supply system when there is no load, a case where a single switching power supply device is operated without load will be described. Even in a switching power supply device operating with no load, power is supplied from the input side to the output side by operating the switching element. This is because the output voltage control circuit of the switching power supply device consumes some power, and this power needs to be supplied.

  Next, a case where the system is operating with no load when a switching power supply system is configured by connecting a plurality of switching power supply apparatuses in parallel will be described.

  When the switching power supply system operates with no load, the switching power supply with the highest output voltage setting value due to variations in the output voltage setting value among the multiple switching power supply devices that make up the system Only the device performs the switching operation, and the remaining switching power supply devices in the system are stopped.

  The switching power supply with the highest output voltage setting value in the switching power supply system consumes the output voltage control circuit of the switching power supply in the same way as a single switching power supply operating with no load. A switching operation is performed to supply power to be transmitted.

  The remaining switching power supply devices having a low output voltage set value in the switching power supply system are in a state in which a voltage higher than their own output voltage set value is applied to the output side. This is a state in which a voltage is applied from the switching power supply device with the highest output voltage setting value to the switching power supply device with the lower output voltage setting value.

  Here, the switching power supply device to which a voltage higher than its own output voltage setting value is externally applied is in a state where the power consumed by its own output voltage control circuit is supplied from the outside, and operates its own switching element. Power need not be supplied. Also, since the externally applied voltage is higher than the set voltage of its own output voltage control circuit, the output voltage control circuit determines that its own output voltage is high, and reduces its output voltage. The operation of the switching element is controlled. By this control, the operation of the switching element is completely stopped.

  At this time, the switching power supply with the higher output voltage set value has almost zero output current, and the switching power supply with the lower output voltage set value has completely zero output current. Since the power supply device has almost the same value, the current balance technique of Patent Document 1 does not function.

(Configuration of switching power supply)
FIG. 6 is a circuit block diagram showing the configuration of one circuit of a conventional switching power supply device constituting the switching power supply system.

  As shown in FIG. 6, the switching power supply device 100 includes a power conversion unit 112 and an output voltage control circuit 122. The output voltage control circuit 122 includes a feedback control circuit 126, a reference voltage source 128, and a PWM control circuit 130.

  The power conversion unit 112 is, for example, a step-down chopper, and includes a switching element 114 using a MOS-FET, a rectifying diode 118, a smoothing inductor 116, and a capacitor 120.

  The power conversion unit 112 converts the input voltage Vin to the input terminals 110 a and 110 b into an intermittent voltage by turning on and off the switching element 114, and rectifies and smoothes the intermittent voltage by the inductor 116, the diode 118, and the output capacitor 120. The output voltage Vo is generated and supplied to the load from the output terminals 121a and 121b.

  Switching element 114 operates to turn on when switching control signal VGS from PWM control circuit 130 is at an H level and to turn off when it is at an L level. The output voltage Vo is controlled by the on-duty of the switching element 114. When the on-duty increases, the output voltage Vo increases, and when the on-duty decreases, the output voltage Vo decreases.

  In FIG. 6, a step-down chopper is used as the power conversion unit 112, but the operation is the same as long as the circuit can perform power conversion by turning on and off the switching element. For example, an insulation type forward converter, flyback converter, etc. But it ’s okay.

  The reference voltage source 128 is a voltage generation circuit that outputs a predetermined reference voltage Vref, and is used to control the output voltage Vo of the power converter 112 to a predetermined output voltage setting value.

  The feedback control circuit 126 includes an error amplifier 138. The error amplifier 138 performs feedback control so that the output voltage Vo becomes a value proportional to the reference voltage Vref. The error amplifier 138 of the feedback control circuit 126 receives the output detection voltage Vsens that is a voltage proportional to the reference voltage Vref and the output voltage Vo divided by the resistors 134 and 136 of the output voltage detection circuit 124.

  The error amplifier 138 of the feedback control circuit 126 outputs a feedback signal VFB that changes according to the error between the reference voltage Vref and the output detection voltage Vsens to the PWM control circuit 130. That is, the error amplifier 138 performs control so that the feedback signal VFB decreases when Vsens> Vref, and performs control so that the feedback signal VFB increases when Vsens <Vref.

  The PWM control circuit 130 includes a PWM comparator 146 and a triangular wave oscillator 148. The PWM comparator 146 receives the triangular wave signal Vtri having a predetermined frequency and amplitude from the triangular wave oscillator 148 and the feedback signal VFB from the feedback control circuit 126, and outputs the output of the PWM comparator 146 to the power conversion unit 112 as the switching control signal VGS. Is done.

  The PWM control circuit 130 performs control so that the switching control signal VGS becomes H level when VFB> Vtri, and performs control so that the switching control signal VGS becomes L level when VFB <Vtri. Therefore, the switching frequency of the switching power supply device 100 is determined by the frequency of the triangular wave oscillator 148. When the feedback signal VFB increases, the on-duty of the switching element 114 increases, and when the feedback signal VFB decreases, the on-duty of the switching element 114 decreases. Become.

  As a result, the output voltage Vo of the switching power supply device 100 is controlled to be a predetermined output voltage set value determined by the reference voltage Vref.

(Operation of switching power supply unit with higher output voltage setting value during parallel operation)
FIG. 7 is a time chart showing operation waveforms of the switching power supply device on the higher output voltage setting value, FIG. 7A shows the input of the error amplifier 138, and FIG. 7B shows the input of the PWM comparator 146. FIG. 7C shows the switching control signal VGS.

  When the switching power supply system is operating with no load, only the switching power supply device with the highest output voltage setting value performs the switching operation, and the other switching power supply devices are in a state where the switching operation is stopped. The operation of the switching power supply on the side where the switching operation is performed in the switching power supply constituting the switching power supply system will be described with reference to FIG.

  Even when the switching power supply system is operating with no load, the switching power supply apparatus in which the switching operation is performed performs control so that the output voltage as the switching power supply system becomes its own output voltage setting value. At this time, the switching power supply device in which the switching operation is performed supplies all of the power consumption on the output side of the switching power supply device constituting the switching power supply system.

  In the switching power supply device in which the switching operation is performed, the feedback signal VFB is controlled so that the output voltage detection signal Vsens becomes equal to the reference voltage Vref, as shown in FIG.

  In addition, when the switching power supply system is in a no-load state, the switching power supply device in which the switching operation is performed is in a state in which almost no power needs to be output. In addition, the power converter 112 operates in a state where the on-duty of the switching element 114 is small. In this state, the feedback signal VFB operates in a state where it is located just below the lower limit of the triangular wave signal Vtri.

(Operation of switching power supply unit with lower output voltage setting value during parallel operation)
FIG. 8 is a time chart showing operation waveforms of the switching power supply device on the side where the output voltage set value is low, FIG. 8A shows the input of the error amplifier 138, and FIG. 8B shows the input of the PWM comparator 146. FIG. 8C shows the switching control signal VGS.

  The operation of the switching power supply having the lower output voltage setting value in the switching power supply constituting the switching power supply system will be described with reference to FIG.

  When the switching power supply system is operating with no load, a voltage higher than its output voltage setting value is applied from the outside, so the power consumption of its output circuit is supplied from the outside. It becomes a state.

  Since the switching power supply device on the side where the output voltage set value is lower is applied with a voltage higher than its own output voltage set value from the outside, the state becomes Vsens> Vref as shown in FIG. In this state, since the feedback control circuit 126 performs control so as to decrease the output voltage, control to decrease the feedback signal VFB is performed.

  The switching power supply device on the side where the output voltage setting value is low will reduce the feedback signal VFB to the lower limit because the voltage applied from the outside to the output side will not decrease even if the feedback signal VFB is decreased. As shown in FIG. 8B, the feedback signal VFB is controlled so as to be separated from the lower limit of the triangular wave signal Vtri, and the state where the switching operation is stopped is maintained.

(Principle of current response deterioration of switching power supply system)
In the switching power supply system operated with no load, the principle that the response time is delayed until the output current increases will be described below.

  When a large output current is suddenly taken out from the switching power supply system, the output voltage of the switching power supply device constituting the system is lowered. In response to a decrease in the output voltage, the switching power supply device is controlled to increase the output voltage by increasing the on-duty of the switching element.

  Specifically, since all of the switching power supply devices constituting the system are in a state of Vsens <Vref, the feedback control circuit 126 performs an operation of raising the feedback signal VFB.

  At this time, the switching power supply device with the higher output voltage setting value shown in FIG. 7 operates immediately at the position where the feedback signal VFB is just below the lower limit of the triangular wave signal Vtri. On the other hand, the on-duty of the switching element 114 becomes large, and it is possible to respond quickly to an increase in output current.

  On the other hand, the switching power supply device with the lower output voltage setting value shown in FIG. 8 is located at a position where the feedback signal VFB is separated from the position where the triangular wave signal Vtri is amplitude, so that the feedback signal VFB increases. However, the switching element 114 cannot operate until the amplitude position of the triangular wave signal Vtri is reached, and cannot respond quickly to an increase in output current.

  For this reason, a switching power supply system in a no-load state can quickly respond to a current that is less than or equal to the current value that can be output by a single switching power supply device that constitutes the system. When trying to output steeply from the system, a response delay of current output occurs.

(Comparison between synchronous rectification and diode rectification)
The problem of the current response in the switching power supply device on the side where the output voltage set value is low becomes conspicuous when the switching power supply device using diode rectification in the power converter 112 is operated in parallel.

  On the other hand, in a switching power supply using synchronous rectification in the power conversion unit, a phenomenon occurs in which a reverse current flows from the output side to the input side. By taking measures to prevent the reverse current as disclosed in Patent Document 2, the problem of current response is also solved at the same time.

  The switching power supply device of Patent Document 2 is configured such that the feedback signal does not fall below the lower limit of the triangular wave signal even when a voltage higher than its output voltage setting value is applied from the output side of the switching power supply device. Yes. In this state, since the feedback signal is positioned within the amplitude of the triangular wave signal, the output current can be increased immediately.

  By the way, a measure for eliminating such a delay in current response according to Patent Document 2 is that the switching element can be operated at the same on-duty at no load or at full load by using synchronous rectification in the power converter. And cannot be applied to a diode rectifier switching power supply.

  This is because when a diode rectification switching power supply device is used with no load, the on-duty must be operated as close to zero as possible. This is because it is necessary to reduce the variation and fluctuation of the triangular wave signal and the feedback signal to the utmost limit, and it is impossible to make a practical circuit.

  The present invention provides a switching power supply device that improves current responsiveness when a current is sharply output from a state where a voltage higher than its output voltage setting value is applied from the outside in a no-load state due to parallel operation. With the goal.

(Switching power supply)
The present invention
A switching element and an output smoothing circuit are provided, the input voltage is converted into an intermittent voltage by turning on and off the switching element, the intermittent voltage is converted into a DC voltage by the output smoothing circuit, and an output voltage is generated. A power converter controlled by on-duty;
Feedback control that includes an error amplifier and a reference voltage source, inputs a predetermined reference voltage output from the reference voltage source and an output detection voltage proportional to the output voltage to the error amplifier, and outputs a feedback signal that changes according to the error between the two. Circuit,
A switching control signal that includes a PWM comparator and a triangular wave oscillator, and that turns a switching element on and off based on a comparison result obtained by inputting a triangular wave signal having a predetermined frequency and amplitude output from a triangular wave transmitter and a feedback signal to the PWM comparator and comparing them. An output PWM control circuit;
In a switching power supply device with
The reference voltage source has a function to increase a predetermined reference voltage,
A switching operation monitoring circuit that suppresses the deviation of the feedback signal from the triangular wave signal by outputting a switching operation stop detection signal to the reference voltage source to increase the predetermined reference voltage when it is detected that the switching element has been turned off for a predetermined time or longer. Is provided.

(Switching operation monitor circuit)
The switching operation monitor circuit includes a diode, a capacitor, a resistor, and a threshold voltage detection circuit, stores electric charge in the capacitor via the diode during the ON period of the switching control signal, and stores the electric charge of the capacitor during the OFF period of the switching control signal. The switching operation stop detection signal is output when the voltage is discharged through the resistor and the voltage of the capacitor is input to the threshold voltage detection circuit and becomes equal to or lower than a predetermined threshold voltage.

(Reference voltage source with a function to increase the reference voltage)
The reference voltage source includes a square wave oscillator with a function to change the duty of the pulse signal, a resistor and a capacitor, and outputs a voltage obtained by smoothing the pulse signal output from the square wave oscillator with a resistor and a capacitor as a reference voltage. It is configured to increase the reference voltage by changing the duty of the square wave oscillator when the switching operation stop detection signal is input, by initially setting the duty of the wave transmitter to a predetermined value and outputting a predetermined reference voltage. The

(Increase of the reference voltage over time)
When the switching operation stop detection signal is input, the reference voltage source changes the duty of the square wave oscillator with the passage of time, thereby increasing the reference voltage with the passage of time.

(Basic effect)
The present invention includes a switching element and an output smoothing circuit, converts an input voltage to an intermittent voltage by turning on and off the switching element, converts the intermittent voltage to a DC voltage by an output smoothing circuit, and generates an output voltage. Has a power converter controlled by the on-duty of the switching element, an error amplifier and a reference voltage source, and inputs a predetermined reference voltage output from the reference voltage source and an output detection voltage proportional to the output voltage to the error amplifier. A feedback control circuit that outputs a feedback signal that changes according to the error between the two, a PWM comparator and a triangular wave oscillator, and a triangular wave signal having a predetermined frequency and amplitude output from the triangular wave transmitter and a feedback signal are input to the PWM comparator. Outputs a switching control signal that turns the switching element on and off based on the comparison results In the switching power supply device including the PWM control circuit, the reference voltage source has a function of increasing the predetermined reference voltage, and when the switching element is detected to be off for a predetermined time or more, the switching operation stop detection is performed. A switching operation monitor circuit is provided that outputs a signal to a reference voltage source to increase a predetermined reference voltage and suppresses the deviation of the feedback signal from the triangular wave signal. For example, outputs of a plurality of switching power supply devices are connected in parallel to a load. When connected and used in parallel operation, switching is detected when an external voltage higher than the output voltage setting value of the switching power supply itself is applied from another switching power supply in the no-load state and the operation of the switching element is stopped. The operation monitor circuit detects the stop of the switching element and increases the reference voltage value. When the voltage rises, the feedback voltage rises, and the switching element operates to cancel the rise of the reference voltage. By repeating this operation, the feedback voltage of the switching power supply device can be in a state where it does not greatly separate from the triangular wave signal. This makes it possible to eliminate the delay in response of the current output when the current is suddenly output from the switching power supply device.

(Effects of switching operation monitor circuit)
The switching operation monitor circuit also includes a diode, a capacitor, a resistor, and a threshold voltage detection circuit. The switching operation signal is stored in the capacitor via the diode during the ON period, and the capacitor charge is stored during the OFF period of the switching control signal. Is connected to the threshold voltage detection circuit and the switching operation stop detection signal is output when the voltage drops below the specified threshold voltage. The reference voltage can be increased by reliably detecting that an external voltage higher than the output voltage setting value of the switching power supply device itself is applied in the no-load state and the operation of the switching element is stopped.

(Effects of a reference voltage source with a function to increase the reference voltage)
The reference voltage source also includes a square wave oscillator with a function to change the duty of the pulse signal, a resistor and a capacitor, and outputs a voltage obtained by smoothing the pulse signal output from the square wave oscillator with a resistor and a capacitor as a reference voltage. The square wave oscillator duty is initially set to a predetermined value and a predetermined reference voltage is output. When a switching operation stop detection signal is input, the square wave oscillator duty is changed to increase the predetermined reference voltage. Thus, the reference voltage can be changed with a simple configuration by changing the duty of the square wave oscillator.

(Effects of increasing reference voltage over time)
In addition, when the switching operation stop detection signal is input, the reference voltage source increases the reference voltage with the passage of time by changing the duty of the square wave oscillator with the passage of time. When the current is steeply output from the switching power supply, the reference voltage is gradually increased, so that the feedback control circuit can be operated more stably than when the reference voltage is increased stepwise.

  Also, by raising the reference voltage beyond the output detection voltage input to the error amplifier, it is possible to increase the voltage difference between the increased reference voltage and the output detection voltage, so the feedback signal rise speed And the delay time until the switching element operates can be further shortened.

The circuit block diagram which showed 1st Embodiment of the switching power supply device by this invention Block diagram showing a switching power supply system that operates in parallel with the outputs of multiple switching power supply units connected in parallel to a load Time chart showing the operating waveform of the switching power supply with higher output voltage setting during parallel operation without load Time chart showing the operating waveform of the switching power supply on the side where the output voltage setting value is low during parallel operation without load In the second embodiment of the switching power supply device, a time chart showing an operation waveform in the case where the reference voltage when the stop of the switching element is detected is increased with time A circuit block diagram showing an embodiment of a conventional switching power supply device Time chart showing the operation waveform of the conventional switching power supply unit with higher output voltage setting value during parallel operation without load Time chart showing the operation waveform of the conventional switching power supply device on the side where the output voltage setting value is low during parallel operation without load

[Circuit configuration of switching power supply unit]
FIG. 1 is a circuit block diagram showing a first embodiment of a switching power supply device according to the present invention.

  As shown in FIG. 1, the switching power supply device 10 of this embodiment includes a power conversion unit 12 and an output voltage control circuit 22. The output voltage control circuit 22 includes a reference voltage source 28 having a voltage raising function, a feedback control circuit 26, a PWM control circuit 30, and a switching operation monitor circuit 32. An output voltage detection circuit 24 is provided on the output side of the power converter 12 and is included in the output voltage control circuit 22.

(Power converter)
The power conversion unit 12 is a non-insulated step-down chopper, the drain of the switching element 14 using a MOS-FET is connected to the positive input terminal 11a, and the anode of the rectifying diode 18 is connected to the source of the switching element 14 And one end of the inductor 16 is connected to the other end of the inductor 16, and the other end of the capacitor 20 and the cathode of the diode 18 are connected to the negative input terminal 11b.

  The power conversion unit 12 is configured by an inductor 16 and a capacitor 20 by converting the input voltage Vin from the input terminals 11a and 11b into an intermittent voltage by turning on and off the switching element 14, and rectifying the intermittent voltage by the diode 18. The output is converted to a DC voltage by being smoothed by a smoothing circuit, and an output voltage Vo is generated and supplied to the load from the output terminals 21a and 21b.

  The output voltage Vo of the power converter 12 is output as a predetermined voltage by controlling the on-duty of the switching element 14.

  In the present embodiment, a non-insulated step-down chopper is used as the power conversion unit 12. However, any circuit that can convert power by turning on and off switching elements may be used. For example, an isolated forward converter or flyback A converter may be used.

(Reference voltage source)
The reference voltage source 28 is a voltage generation circuit that normally outputs a predetermined reference voltage Vref, and raises the reference voltage Vref when the switching operation stop detection signal Vstop output from the switching operation monitor circuit 32 is input. It has a function.

  As an example of the reference voltage source 28 having a voltage raising function, in this embodiment, the reference voltage source 28 includes a square wave oscillator 40, a resistor 42, and a capacitor 44. A pulse signal output from the square wave oscillator 40 is referred to as a resistor 42. The voltage smoothed by the capacitor 44 is output as the reference voltage Vref.

  The reference voltage source 28 increases the reference voltage Vref by performing control to increase the duty of the H level of the pulse signal output from the square wave oscillator 40 when the switching operation stop detection signal Vstop is input.

  For example, the square wave oscillator 40 outputs a pulse signal of 5 volts as the H level and 0 volts as the L level. At this time, if the duty of the square wave oscillator 40 is set to 50%, it is smoothed by the resistor 42 and the capacitor 44 to obtain the reference voltage Vref = 2.5 volts, and if the duty is set to 55%, Vref = 2. 75. Volts are obtained.

(Feedback control circuit)
The feedback control circuit 26 includes an error amplifier 38. The error amplifier 38 receives the output detection voltage Vsens, which is a voltage proportional to the reference voltage Vref and the output voltage Vo divided by the resistors 34 and 36 of the output voltage detection circuit 24. The error amplifier 38 outputs a feedback signal VFB that changes according to an error between the reference voltage Vref and the output detection voltage Vsens to the PWM control circuit 30.

  That is, the error amplifier 38 of the feedback control circuit 26 performs control so that the feedback signal VFB decreases when Vsens> Vref, and performs control so that the feedback signal VFB increases when Vsens <Vref.

(PWM control circuit)
The PWM control circuit 30 includes a PWM comparator 46 and a triangular wave oscillator 48. The triangular wave oscillator 48 outputs a triangular wave signal Vtri having a predetermined frequency and amplitude. The triangular wave signal Vtri and the feedback signal VFB are input to the PWM comparator 46, and a switching control signal VGS for turning on and off the switching element 14 is output based on the result of comparing the triangular wave signal Vtri and the feedback signal VFB.

  That is, the PWM control circuit 30 performs control so that the switching control signal VGS becomes H level when VFB> Vtri, and performs control so that the switching control signal VGS becomes L level when VFB <Vtri.

  Thereby, the switching frequency of the switching power supply device 10 is determined by the frequency of the triangular wave oscillator 48. The on-duty of the switching element 14 is controlled by the voltage level of the feedback signal VFB. When the feedback signal VFB increases, the on-duty of the switching element 14 increases, and when the feedback signal VFB decreases, the on-duty of the switching element 14 decreases. Become.

(Switching operation monitor circuit)
The switching operation monitor circuit 32 is a circuit that monitors the on / off operation of the switching element 14, and uses the switching operation stop detection signal Vstop as a reference voltage when the on / off operation of the switching element 14 has not been performed for a predetermined time or longer. Output to the source 28 to raise the reference voltage Vref.

  In the present embodiment, the switching operation monitor circuit 32 includes, as an example, a diode 50, a resistor 52, a capacitor 54, and a threshold voltage detection circuit 56. A switching control signal VGS is input to the switching operation monitor circuit 32, and the capacitor 54 is charged via the diode 50 when the switching control signal VGS is at the H level. When the switching control signal VGS is at the L level, the charge stored in the capacitor 54 is discharged through the resistor 52, so that the voltage of the capacitor 54 decreases.

  When the switching element 14 is turned on / off by the switching control signal VGS, the voltage of the capacitor 54 is maintained at a certain value or more, but the on / off operation of the switching element 14 is stopped and turned off. If this continues, the voltage of the capacitor 54 becomes equal to or lower than a predetermined threshold voltage Vth. A threshold voltage detection circuit 56 is connected to the capacitor 54. When the voltage of the capacitor 54 becomes equal to or lower than a predetermined threshold voltage Vth, a switching operation stop signal Vstop is output to the reference voltage source 28, and the reference voltage Vref. To raise.

[Overview of switching power supply system for parallel operation]
FIG. 2 is a block diagram showing a switching power supply system in which outputs of a plurality of switching power supply apparatuses are connected in parallel to a load and operated in parallel.

  As shown in FIG. 2, the switching power supply system of the present embodiment includes a plurality of switching power supply devices 10-1 to 10-n having the same configuration as the switching power supply device 10 of the first embodiment of FIG. The input power supply 11 is connected in parallel to the input terminals of the power supply apparatuses 10-1 to 10-n, and the output terminals of the switching power supply apparatuses 10-1 to 10-n are connected in parallel to the load 21. The power is supplied to the load 21 by the parallel operation of -1 to 10-n.

  Here, the switching power supply device 10-1 functions as a master power supply device, and the remaining switching power supply devices 10-2 to 10-n function as slave power supply devices.

  When performing parallel operation with the switching power supply devices 10-1 to 10-n, each of the switching power supply device 10-1 set as a master by balance control and the switching power supply devices 10-2 to 10-n set as slaves. The output voltage Vo becomes the same, and each output current Io is (rated / n) obtained by dividing the rated current Irated to be supplied to the load 21 by the number n of power supply devices.

  The balance control when performing parallel operation with the switching power supply devices 10-1 to 10-n is realized by serial communication using a general-purpose UART module, for example. UART module is an abbreviation for Universal Asynchronous Receiver Transmitter module.

  From the switching power supply devices 10-1 to 10-n, the communication terminal of the UART module is taken out as an INF terminal and connected to each other by the transmission line 60.

  The switching power supply device 10-1 set as the master generates the setting information from the output voltage target value of itself, generates the setting information of the output current target value from the output current detection value, and generates the serial communication data signal. In addition, the power is transmitted from the INF terminal of the UART module via the transmission line 60 to the switching power supply devices 10-2 to 10-n set as slaves.

  The switching power supply 10-10 to 10 -n set as the slave transmits the serial communication data signal by the UART module via the INF terminal, so that the switching power supply 10-10 set as the master transmits the serial communication data signal. Receives output voltage target value setting value information and output current target value setting information, and outputs its own output voltage so that the difference between the master output voltage and output current and its own output voltage and output current is below a certain value. Set the target value and output current target value.

  By this operation, the switching power supply devices 10-2 to 10-n set as slaves are controlled so that their output voltage and output current are the same as the switching power supply devices 10-1 set as masters. The output voltage and the output current of the switching power supply devices 10-1 to 10-n connected in parallel to 21 are balanced.

  The control for balancing the output voltage and the output current in the parallel operation is performed by, for example, the output voltage received from the switching power supply apparatus 10-1 in which the duty of the square wave oscillator 40 provided in the reference voltage source 28 in FIG. Control is performed to set the reference voltage Vref corresponding to the target value and the output current target value.

  Thus, the balance control in the case of performing the parallel operation with the switching power supply devices 10-1 to 10-n is a function in which the control is performed so that the difference between the output voltage and the output current of each switching power supply device becomes a certain value or less. Therefore, it functions effectively when a current of a certain value or more is supplied to the load 21, but in a no-load state in which the operation of the load 21 is stopped, the switching power supply devices 10-1 to 10-n Since the output current is almost zero or completely zero, and the switching power supply devices 10-1 to 10-n all have almost the same value as the output current, the balance control does not function.

[Operation of switching power supply unit with higher output voltage setting during parallel operation]
FIG. 3 is a time chart showing operation waveforms of the switching power supply device on the side where the output voltage set value is high, FIG. 3A shows the input of the error amplifier 38, and FIG. 3B shows the input of the PWM comparator 46. 3C shows the switching operation stop detection signal Vstop, FIG. 3D shows the input of the threshold voltage detection circuit 56 which is the voltage of the capacitor 54, and FIG. 3E shows the switching control. Signal VGS is shown.

  Here, since the balance control of the switching power supply system functions when there is a difference of a certain value or more in the load current due to the parallel operation of the plurality of switching power supply apparatuses 10, the switching power supply system is operated with no load. Since there is almost no difference in load current, balance control of the switching power supply system does not function.

  In addition, when the switching power supply system operates with no load, the output voltage setting value is the highest value among the plurality of switching power supply devices constituting the system due to variations in the output voltage setting value. Only the switching power supply device actively performs a switching operation to supply current to the switching power supply system.

  The operation of the switching power supply device 10 on the side where the output voltage set value is high during parallel operation will be described with reference to FIG.

  The switching power supply device 10 on the higher output voltage setting value performs control so that the output voltage as the switching power supply system becomes its own output voltage setting value. At this time, the switching power supply device 10 on the side where the output voltage setting value is high supplies all of the power consumption on the output side of the switching power supply device 10 constituting the switching power supply system. Therefore, the switching power supply device 10 on the side where the output voltage set value is higher during the parallel operation has the same operation as the switching power supply device 10 operating alone.

  As shown in FIG. 3A, in the switching power supply device 10 on the side where the output voltage set value is high, the feedback signal VFB is controlled by the feedback control circuit 26 so that the output detection voltage Vsens becomes equal to the reference voltage Vref.

  When the switching power supply system is in a no-load state, the switching power supply device 10 on the side where the output voltage setting value is high is in a state where almost no power needs to be output. Therefore, as shown in FIG. The signal VFB operates in a state where it is positioned just below the lower limit of the triangular wave signal Vtri, and as shown in FIG. 3E, the H level period of the switching control signal VGS is shortened, and the on-duty of the switching element 14 is small. Operate in a state.

  As shown in FIG. 3D, the capacitor 54 of the switching operation monitor circuit 32 is periodically charged by the H level of the switching control signal VGS, and the voltage VC of the capacitor 54 is the threshold voltage detection circuit. 56 threshold voltage Vth or less. Therefore, as shown in FIG. 3C, the switching operation monitor circuit 32 is in the L level without outputting the switching operation stop detection signal Vstop, and the reference voltage source 28 performs control to increase the reference voltage Vref. It is kept at a predetermined reference voltage Vref.

  The operation of the switching power supply device 10 on the side where the output voltage set value is high during such parallel operation is the same operation even when the switching power supply device 10 is operating alone. When the diode rectification switching power supply 10 is operated with no load, the switching element is operated with the on-duty of the switching element as close to zero as possible. However, when the switching element is operating, the switching operation monitor circuit 32 is operated. 1 does not output the switching operation stop detection signal Vstop, so that the reference voltage source 28 having the voltage increasing function does not affect the control of the switching element, and the switching power supply of the present embodiment shown in FIG. The device 10 has been described as an example of use in the switching power supply system that performs the parallel operation shown in FIG.

[Operation of switching power supply with lower output voltage setting during parallel operation]
FIG. 4 is a time chart showing operation waveforms of the switching power supply device on the side where the output voltage set value is low. FIG. 4A shows the input of the error amplifier 38, and FIG. 4B shows the input of the PWM comparator 46. 4C shows the switching operation stop detection signal Vstop, FIG. 4D shows the input of the threshold voltage detection circuit 56 which is the voltage of the capacitor 54, and FIG. 4E shows the switching control. Signal VGS is shown.

  With reference to FIG. 4, the operation of the switching power supply 10 on the side where the output voltage set value is low during parallel operation will be described as follows.

  When the switching power supply system is operating with no load, a voltage higher than its output voltage setting value is applied from the outside, so the power consumption of its output circuit is supplied from the outside. It becomes a state.

  As shown in the switching operation stop non-detection period T1 in FIG. 4A, the switching power supply device 10 on the lower output voltage set value side is applied with a voltage higher than its own output voltage set value from the outside. , Vsens> Vref. In this state, the feedback control circuit 26 performs control so as to decrease the output voltage. Therefore, as shown in FIG. 3B, control for decreasing the feedback signal VFB is performed, and the feedback signal VFB gradually increases. And becomes equal to or lower than the triangular wave signal Vtri, and the switching operation of the switching element 14 at the frequency of the triangular wave signal Vtri is stopped. At this time, the decrease rate of the feedback signal VFB is determined by the response speed of the feedback control circuit 26.

  When the switching operation of the switching element 14 is stopped, the switching control signal VGS becomes L level, and as shown in FIG. 4D, the capacitor 54 of the switching operation monitor circuit 32 is not charged, and the voltage VC of the capacitor 54 decreases. . When the voltage VC of the capacitor 54 falls below the threshold voltage Vth set in the threshold voltage detection circuit 56 of the switching operation monitor circuit 32 at time t1, as shown in FIG. An operation stop detection signal Vstop is output.

  When the switching operation stop detection signal Vstop which becomes H level is input, the reference voltage source 28 increases the reference voltage Vref so as to be higher than the output detection voltage Vsens as shown in FIG. . As shown in the switching operation stop detection period T2, in the state of Vsens <Vref, as shown in FIG. 4B, the feedback control circuit 26 performs control to increase the feedback signal VFB. The rising speed of the feedback signal VFB at this time is determined by the response speed of the feedback control circuit 26.

  As shown in FIG. 4B, when the feedback signal VFB rises and becomes VFB> Vtri at time t2, as shown in FIG. 4E, a switching control signal VGS that becomes H level is output, The switching element 14 is turned on. Further, when the switching control signal VGS which becomes H level is output, the capacitor 54 of the switching operation monitor circuit 32 is charged and the capacitor voltage VC rises and exceeds the threshold voltage Vth of the threshold voltage detection circuit 56. The switching operation stop detection signal Vstop which becomes L level is output.

  When the switching operation stop detection signal Vstop that is at L level is input, the reference voltage source 28 is released from the rising operation of the reference voltage Vref and returned to the normal voltage, and the same operation is repeated thereafter.

  For this reason, in the switching power supply 10 on the side to which a voltage higher than its output voltage set value is applied from the outside in parallel operation, the feedback signal VFB is not separated from the triangular wave signal Vtri, and is near the lower limit of the triangular wave signal Vtri. Will continue to work.

(Advantages of the first embodiment)
By using the switching power supply device of the first embodiment in a switching power supply system that operates in parallel, a switching power supply system in a no-load state switches a current that is greater than or equal to the current value that can be output by one switching power supply device that constitutes the system. When trying to output steeply from the power supply system, it is possible to eliminate the delay in response of the current output even in the switching power supply device on the side where the output voltage setting value is low, and the capacitor on the output side of the switching power supply device There is no need to increase the size, and a small-sized and low-cost switching power supply device can be produced.

  Moreover, even when the switching power supply device of this embodiment is used alone, it does not adversely affect the operation at no load.

[Second Embodiment of Switching Power Supply Device]
FIG. 5 is a time chart showing operation waveforms of the switching power supply device on the side where the output voltage set value is low in the second embodiment of the switching power supply device. FIG. 5A shows the input of the error amplifier 38. 5B shows the input of the PWM comparator 46, FIG. 5C shows the switching operation stop detection signal Vstop, FIG. 5D shows the input of the threshold voltage detection circuit 56, and FIG. ) Indicates the switching control signal VGS.

(Configuration of Second Embodiment)
The switching power supply device of the present embodiment has the same configuration as the switching power supply device 10 of the first embodiment shown in FIG. 1, but is based on the reference voltage source 28 when the switching operation stop detection signal Vstop that becomes H level is input. The method of increasing the reference voltage Vref is different.

  The reference voltage source 28 of the present invention needs to perform control to increase the reference voltage Vref so as to be larger than the output detection voltage Vsens when the switching operation stop detection signal Vstop which becomes H level is input.

  In the first embodiment shown in FIG. 1, the reference voltage Vref is controlled stepwise in two stages, that is, the voltage after normal operation and the voltage that has been raised by the input of the switching operation stop detection signal Vstop that becomes H level. Therefore, it is necessary to set the increased reference voltage Vref in anticipation of variations in the output voltage setting value of the switching power supply 10 that is operated in parallel. When the variation is large, it is necessary to set a large value for the reference voltage Vref after the increase. However, if the voltage difference before and after the reference voltage Vref is increased is large, the operation of the feedback control circuit 26 may become unstable due to a step change of the reference voltage Vref.

  In this embodiment, the reference voltage Vref in the switching operation stop detection period is increased with an inclination as shown in the switching operation stop detection period T2 in FIG. Even when Vref is greatly increased, the feedback control circuit 26 can be stably operated.

  The switching power supply device of this embodiment is configured by the same circuit as the switching power supply device 10 of the first embodiment shown in FIG. 1, and controls the reference voltage source 28 having a voltage raising function as follows. .

  As shown in FIG. 5A, when the switching operation stop detection signal Vstop is input at time t1, the reference voltage source 28 performs control to increase the duty of the square wave oscillator 40 with time. By this control, the reference voltage Vref gradually increases with time. When the reference voltage Vref rises and Vsens <Vref is reached at time t2, the feedback control circuit 26 performs control to raise the feedback signal VFB, as shown in FIG. 5B.

  Even if Vsens <Vref at time t2, the reference voltage Vref continues to rise. As the difference between the output detection voltage Vsens and the reference voltage Vref increases, the rate of increase of the feedback signal VFB increases, so that the feedback signal VFB can be quickly reached the lower limit of the triangular wave signal Vtri.

  When feedback signal VFB reaches the lower limit of triangular wave signal Vtri at time t3, switching element control signal VGS at H level is output, and switching operation stop detection signal Vstop at L level is output. When the switching operation stop detection signal Vstop which becomes L level is input, the duty of the square wave oscillator 40 of the reference voltage source 28 is returned to the normal state, and the reference voltage Vref returns to the normal voltage. Thereafter, the same operation is repeated.

(Advantages of the second embodiment)
In the first embodiment, since the reference voltage Vref is controlled stepwise in two steps, that is, the voltage during normal operation and the voltage after the increase, if the voltage difference before and after the reference voltage Vref is increased is large, the reference voltage Vref However, in the second embodiment, the control is performed so that the reference voltage Vref is gradually increased as time elapses. The feedback control circuit 26 can be operated stably.

  In the first embodiment, it is difficult to increase the voltage difference before and after the reference voltage Vref is increased. Therefore, it is difficult to increase the voltage difference between the increased reference voltage Vref and the output detection voltage Vsens. In the second embodiment, since the voltage difference between the increased reference voltage Vref and the output detection voltage Vsens can be increased, the rising speed of the feedback signal VFB is increased, and the system is switched from the switching power supply system in the no-load state. When the switching power supply system steeply outputs a current that is greater than or equal to the current value that can be output by a single switching power supply device, the delay time until the switching element operates can be shortened.

[Modification of the present invention]
The above embodiment is an example in which an external voltage higher than the output voltage is applied to the output of the power conversion unit from another switching power supply device in the no-load state of the switching power supply system that performs parallel operation of the plurality of switching power supply devices. In the same way, even if the switching power supply operating as a single unit is in a no-load state and an external voltage higher than the output voltage is applied to the output of the power converter, the reference voltage is similarly increased. By doing so, it is possible to suppress the deviation of the feedback signal from the triangular wave signal, and to eliminate the response delay of the current output when trying to output the current sharply from the switching power supply device.

  The present invention includes appropriate modifications without impairing the object and advantages thereof, and is not limited by the numerical values shown in the above embodiments.

10: switching power supply device 11: input power supply 12: power converter 14: switching element 16: inductor 18, 50: diode 20, 44, 54: capacitor 21: load 22: output voltage control circuit 24: output voltage detection circuit 26: Feedback control circuit 28: Reference voltage source 30: PWM control circuits 34, 36, 42, 52: Resistor 32: Switching operation monitor circuit 38: Error amplifier 40: Square wave oscillator 46: PWM comparator 48: Triangular wave oscillator 56: Threshold value Voltage detection circuit 60: transmission line

Claims (4)

A switching element and an output smoothing circuit; converting the input voltage to an intermittent voltage by turning on and off the switching element; generating the output voltage by converting the intermittent voltage to a DC voltage by the output smoothing circuit; and Is a power converter controlled by the on-duty of the switching element;
An error amplifier and a reference voltage source are provided, and a predetermined reference voltage output from the reference voltage source and an output detection voltage proportional to the output voltage are input to the error amplifier, and a feedback signal that changes according to the error between the two is output. A feedback control circuit to
A switching control signal that includes a PWM comparator and a triangular wave oscillator, and that turns on and off the switching element based on a result of comparing the feedback signal with a triangular wave signal having a predetermined frequency and amplitude output from the triangular wave transmitter. PWM control circuit that outputs
In a switching power supply device with
The reference voltage source has a function of increasing the predetermined reference voltage;
When it is detected that the switching element has been turned off for a predetermined time or more, a switching operation stop detection signal is output to the reference voltage source to raise the predetermined reference voltage, and from the triangular wave signal of the feedback signal A switching power supply device is provided, which is provided with a switching operation monitor circuit that suppresses the difference between the two.
(Switching operation monitor circuit)
In the switching power supply device according to claim 1,
The switching operation monitor circuit includes a diode, a capacitor, a resistor, and a threshold voltage detection circuit, and stores charge in the capacitor via the diode during the ON period of the switching control signal, and during the OFF period of the switching control signal. The capacitor charge is discharged through the resistor, and the switching operation stop detection signal is output when the voltage of the capacitor is input to the threshold voltage detection circuit and falls below a predetermined threshold voltage. A switching power supply device configured as described above.
(Reference voltage source with a function to increase the reference voltage)
In the switching power supply device according to claim 1,
The reference voltage source includes a square wave oscillator having a function of changing the duty of a pulse signal, a resistor and a capacitor, and a voltage obtained by smoothing the pulse signal output from the square wave oscillator by the resistor and the capacitor is used as a reference voltage. Output, the duty of the square wave oscillator is initially set to a predetermined value, the predetermined reference voltage is output, and when the switching operation stop detection signal is input, the duty of the square wave oscillator is changed to change the duty A switching power supply device configured to increase a predetermined reference voltage.
(Increase of the reference voltage over time)
4. The switching power supply device according to claim 3, wherein when the switching operation stop detection signal is input, the reference voltage source changes the duty of the square wave oscillator according to the passage of time. A switching power supply device characterized in that a reference voltage is raised as time passes.

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