JP2016042765A - Switching power supply apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problem: In the flyback type of multi-output switching power supply comprised of one transformer, a reference power supply section with a feedback circuit can output a stable DC voltage, while a power supply section without a feedback circuit varies a voltage with load fluctuations in the reference power supply section.SOLUTION: A reference power supply section includes a current detector for detecting a load current and a current variable dummy resistor circuit (voltage-current converter) for keeping an electric current of a rectifier filter circuit constant, and controls the current variable dummy resistor circuit so that a total of the load current and an electric current of the dummy resistor circuit becomes constant.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an output voltage stabilization circuit of a flyback type multi-output switching power supply device that outputs a plurality of DC voltages using a single transformer.

  Usually, in a switching power supply apparatus configured to obtain a plurality of output voltages with one transformer, one of the plurality of output voltages on the secondary side is used as a reference in order to control the switching element on the primary side of the transformer. Set the output voltage. Based on this reference output voltage, the output voltage value of another output voltage is set by the ratio of the number of windings to the reference output voltage.

  FIG. 4 shows a circuit configuration of a flyback switching power supply that outputs two output voltages with a single transformer described in Patent Document 1. The secondary output circuit is configured to generate two output voltages with respect to the common potential. The series circuit of the primary winding P1 of the transformer T1 and the switching element (here, MOSFET) Q1 is connected in parallel with the DC power source V. The control terminal (gate) of the switching element Q1 is connected to the control circuit 21 and the control circuit 21 is controlled. A phototransistor PT of a photocoupler is connected to the terminal. The secondary winding S1 of the transformer T1 is connected to the anode of the rectifier diode D1, the cathode of the rectifier diode D1 is connected to the smoothing capacitor C1, and the load RL2 is connected in parallel to the capacitor C1. A dummy resistor circuit 32 including a Zener diodes ZD1 and ZD2, a transistor Q2, and resistors R1 and R2 is connected in parallel with the capacitor C1 to constitute a sub output circuit 11a.

The anode of the rectifier diode D2 is connected to the secondary winding S2 of the transformer T1, the smoothing capacitor C2 is connected to the cathode of the rectifier diode D2, and a load RL1 is connected in parallel with the capacitor C2. Further, in parallel with the capacitor C2, a parallel circuit of a photodiode PD of a photocoupler and a resistor R3, a series circuit of a resistor R4 and a shunt regulator IC1, an output voltage is applied to the detection terminal of the shunt regulator IC1 by resistors R6, R7, and R8. The divided output voltage detection voltage is connected. Further, a series circuit of a resistor R5 and a capacitor C3 is connected between a connection point between the resistor R4 and the shunt regulator IC1 and a connection point between the resistors R7 and R8. As described above, the main output circuit 12 is constituted by the secondary winding S2 of the transformer T1.

The negative point of the main output circuit 12 (terminal on the side not connected to the diode D2 of the S2 winding) and the negative point of the sub output circuit 11a (terminal on the side not connected to the diode D1 of the S1 winding) are connected, It becomes a common potential point. A series circuit of a Zener diode ZD3 and a diode D3 is connected between a connection point between the Zener diode ZD2 and the resistor R2 of the sub output circuit 11a and a connection point between the resistors R7 and R8 of the main output circuit 12. .

In such a configuration, the voltage of the main output circuit is fed back to the primary side control circuit 21 by the photocoupler (photodiode PD and phototransistor PT) and is controlled at a constant voltage, so that it is stable against fluctuations in the load RL1. is there. On the other hand, in the sub output circuit 11a, the dummy resistor circuit 32 suppresses the output voltage so as not to exceed the voltage determined by the Zener diodes ZD1 and ZD2 due to load fluctuation or the like. Further, when the dummy resistor circuit 32 of the sub output circuit 11a operates, the detection voltage of the main output circuit is increased by a series circuit of the Zener diode ZD3 and the diode D3 so as to suppress the voltage rise. The present embodiment is a configuration example in which a dummy resistor circuit is used in order to suppress a voltage increase on the side not provided with feedback in a circuit configuration having a common potential point.

FIG. 5 shows a circuit configuration of a conventional switching power supply apparatus when a plurality of output circuits are not connected to a common potential. It is the structural example which extended and connected the example using the dummy resistance described in patent document 2, 3 to each output circuit. DM1 to DM3 are dummy resistors.
The transformer T includes a primary winding W1 and a plurality of secondary windings W2 to W5. A PWM (pulse width modulation) comprising a series circuit of a primary winding W1, a switching element Q11, and a current detection resistor R14 connected in parallel to a DC power source DP and configured by an oscillator Osc, a flip-flop FF, a comparator (comparator) CP, and the like. The control circuit 11 controls the ON time width of the switching element Q11. The winding W5, the diode 15 and the capacitor C15 are circuits for generating a control power source of the PWM control circuit. On the other hand, the outputs of the secondary windings W2 to W4 are rectified by the rectifier diodes D12 to D14, and are smoothed by the electrolytic capacitors C12 to C14 to be a DC power supply that outputs voltages V2 to V4. Each of these power supplies is supplied to loads LD1 to LD3, respectively.

With such a configuration, when the switching element Q11 is on, the voltage Vin of the DC power source DP is applied to the primary winding W1 to pass a current Id, energy is stored in the transformer T, and when the switching element Q11 is off, the transformer The energy stored in T is discharged from W2 to W5 of the secondary winding as an output current.
As a feedback circuit that connects the primary side and the secondary side of the transformer T, a detection circuit is provided in the output voltage V2 generation unit on the secondary side. This circuit uses a shunt regulator IC11, and has resistors R11 and R12 for setting the output voltage Vr from a reference voltage Vref and a divided value of the output voltage V2. The reference voltage Vref and the DC output of the shunt regulator IC11 are provided. The result of comparison with the voltage V2 is transmitted as a signal Vm from the photodiode PD11 to the phototransistor PT11. The comparator CP in the primary PWM control circuit 11 compares the signal Vm of the phototransistor PT11 with the current detection voltage Vs generated by the current detection resistor R14 and the primary current Id. The comparison result is transmitted to the on / off control terminal of the switching element Q11 via the flip-flop FF in the PWM control circuit 11.

As an operation, when the value of the above-described secondary side DC output voltage V2 exceeds the reference voltage Vref, the signal Vm of the phototransistor PT11 is lowered, and when the value becomes lower than the current detection voltage Vs, the flip-flop FF Is inverted, and the switching element Q11 is switched from on to off. Therefore, when the current of the power source that generates the output voltage V2 is small (at the time of light load), the voltage value of the output voltage V2 reaches Vref quickly, so the on-time of the switching element Q11 is shortened. On the other hand, when the current is large (at the time of heavy load), the time until the voltage value of the output voltage V2 reaches Vref becomes longer, so the on-time of the switching element Q11 becomes longer.

With such an operation, a PWM (pulse width modulation) operation is performed, and the detection voltage divided by the resistors R11 and R12 is used as the reference voltage regardless of the state of the load (the amount of output current). It becomes the same voltage value as Vref and is stabilized.
In the switching operation, when the switching element Q11 is turned from on to off, the spike voltage induced by the primary leakage inductance (not shown) of the transformer T is generated by the diode D11 and the zener diode ZD11 which are snubber circuits. The voltage is clamped by flowing Iz. Further, if the voltage value of the Zener diode ZD11 is reduced, the peak value of the spike voltage can be lowered.

Of the output voltages on the secondary side in the above operation, it is expressed as follows using the examples of V2 and V3.
V2 = (n2 / n1) * Vin * D-Vf12 Formula 1
V3 = (n3 / n1) * Vin * D−Vf13 Expression 2
In the above formulas 1 and 2, Vf12 and Vf13 are forward drop voltages of the rectifier diodes D12 and D13. D is a ratio of the on time to the off time of the switching element Q11 and changes so that V2 becomes a specified voltage. n1 is the number of turns of the primary winding W1, and n2 and n3 are the numbers of turns of the secondary windings W2 and W3, respectively.
In this conventional system, the output voltage V2 including the feedback circuit is stable as described above. However, the voltages of the other output voltages V3 to V5 vary depending on the state of the load LD1 connected to the output voltage V2 (current variation). The reason is in D and Vf12 as shown in Equation 1. That is, the on / off time ratio D and the forward drop voltage Vf12 of the rectifier diode change according to the magnitude of the current I.

When the load LD1 is light, since the current I is small, D and Vf12 are also small, and the output voltage of each power source without feedback is low. On the other hand, when the load LD1 is heavy, the current I increases and both D and Vf12 increase, so the output voltage of each power supply without feedback increases. This will be described with reference to FIG. In this example, the voltage value of the output voltage V3 increases in proportion to the current I. Since the output voltage V2 includes the feedback circuit as described above, it is constant without fluctuation. Since the output voltages V4 and V5 increase in the same manner as V3, V3 will be described as an example here.

In this example, the output voltage V2 is provided with a feedback circuit because it is required to have the least voltage fluctuation because of the power supply voltage used for controlling the apparatus. The power supply voltage varies depending on the state of the applied device, the presence / absence of a function, and the addition of a function (generally adding an optional function), and the current I varies greatly over a long time. This variation is from the minimum time Imin to the maximum time Imax, and the normal change range is large. Since the output voltage V3 drives an analog circuit or a device drive circuit to a load in the application apparatus, there is a variation allowable range from Vmin to Vmax in order to protect its operation performance, life, and the like. Under such circumstances, when the current I fluctuates from Imin to Imax, a large voltage fluctuation ΔV1 occurs in the output voltage V3. Furthermore, when the current I is small, the current Imin may fall below the allowable fluctuation range Vmin. Note that the case where the voltage exceeds Vmax is likely to occur when the current I is large and the load on the power supply is low. Usually, a dummy resistor or voltage suppressor (zener diode) that does not involve large power consumption is used. Yes. The dummy resistor DM2 of the circuit that outputs the voltage V3 and the dummy resistor DM3 of the circuit that outputs the voltage V4 play this role.

As a countermeasure for the above problem, there is a method of suppressing the influence on the other output circuits due to the fluctuation of the load LD1 by raising the current I using the dummy resistor DM1. The dummy resistor DM1 plays this role. This is shown in FIG. When the current I2 is passed through the dummy resistor DM1, the maximum and minimum fluctuation ratio of the current I is reduced, so that the voltage fluctuation of the output voltage V3 is also reduced to ΔV2. In addition, since the current I2 is added to the current I1min in the voltage fluctuation range, it is possible to ensure Vmin of the allowable fluctuation range or more.

JP 2013-255362 A JP 2005-341695 A JP-A-63-133867

As described above, in a configuration in which a dummy resistor and a switch circuit are provided in a circuit without a feedback circuit and the switch circuit is turned on when the output voltage rises and this dummy resistor is connected, the maximum voltage can be suppressed. The effect of suppressing the voltage fluctuation range due to the load fluctuation of the circuit including the feedback circuit cannot be achieved. Further, in the configuration in which the dummy resistor is connected to the circuit including the feedback circuit, there is an effect of suppressing the voltage variation range accompanying the load variation of the circuit including the feedback circuit, but the effect is small. In order to increase the effect, it is necessary to increase the size of the dummy resistor to be connected. As a result, power consumption and loss are large, and the device is large. Furthermore, since the output voltage of each power supply is set to be high, there is a drawback that the power consumption of each power supply increases. Accordingly, an object of the present invention is to provide a switching power supply apparatus that can reduce and stabilize output voltage fluctuations of a plurality of power supplies other than a reference power supply.

In order to solve the above-described problem, in the first invention, a transformer having a primary winding and a plurality of secondary windings, a switching element connected in series to the primary winding, and the switching element A control circuit for controlling the on-time width of the output voltage to control the output voltage, a rectifying / smoothing circuit for rectifying and smoothing each output of the secondary winding, and one output serving as a reference voltage among the rectifying / smoothing circuits In a flyback type multi-output switching power supply device comprising: an output voltage detection circuit that sends a feedback signal to the control circuit as a control signal for detecting the voltage of and controlling the on-time width;
A variable current that controls the sum of the load current detector that detects the current flowing in the load connected to the reference output and the load current that is connected to the output of the rectifying and smoothing circuit to a constant current value. A mold dummy resistor circuit.

In a second aspect of the invention, in the flyback multi-output switching power supply apparatus according to the first aspect of the invention, the value of the current flowing through the rectifying / smoothing circuit of the reference output becomes a constant current value regardless of a change in load. In addition, the current variable dummy resistor circuit is controlled.
According to a third aspect of the invention, in the flyback multi-output switching power supply device according to the first or second aspect of the invention, the constant current value flowing through the reference output rectifying and smoothing circuit is the maximum current value of the load. .

  According to a fourth aspect of the invention, in the flyback multi-output switching power supply device according to the first to third aspects of the invention, the variable current dummy resistor circuit includes a reference value provided in a control circuit and a load current detector. The voltage-current converter is controlled by a control amount generated based on a deviation from the output.

  In the present invention, in a flyback type multi-output switching power supply device, a load current detector for detecting a current flowing in a load connected to a reference output having a voltage feedback circuit and an output of a rectifying and smoothing circuit are connected. Current variable type dummy resistance circuit, and the current variable type dummy resistance circuit is controlled so that the sum of the load current and the load current becomes a constant current value, the load current of the reference output circuit varies. Even so, the output current of the rectifier circuit is constant. As a result, even if the load of the reference output circuit fluctuates, the control amount does not fluctuate, so that an output that does not include voltage feedback does not fluctuate. In addition, since the dummy resistance can be reduced below the maximum load capacity, the power supply capacity can be reduced and the apparatus can be downsized.

1 is a circuit diagram showing a first embodiment of the present invention. It is a circuit diagram which shows the specific example of a voltage-current converter. It is operation | movement explanatory drawing of the Example of FIG. 6 is a circuit diagram example A of a conventional switching power supply device. FIG. 4B is a circuit diagram example B of a conventional switching power supply device. FIG. 6 is an operation explanatory diagram A of the switching power supply device shown in FIG. 5. FIG. 6 is an operation explanatory diagram B of the switching power supply device shown in FIG. 5.

  The gist of the present invention is that in a flyback multi-output switching power supply device, a load current detector for detecting a current flowing in a load connected to a reference output having a voltage feedback circuit, and an output of a rectifying and smoothing circuit And a variable current dummy resistor circuit (voltage-current converter) is controlled so that the sum of the load current and the load current becomes a constant current value. is there.

  FIG. 1 shows a first embodiment of the present invention. This switching power supply circuit is a power supply that outputs voltages V2 to V5 to the secondary side. The description of the same part as before is omitted, and the different part will be described. The output voltage V2 is generated by rectifying and smoothing the output of the secondary winding W2 by the rectifier diode D12 and the smoothing capacitor C12. Unlike the prior art, this output voltage V2 line is connected to a current detector Cs for detecting a current I1 flowing through the load LD1 and a voltage-current converter VIC as a current variable dummy resistor circuit. The detection voltage of the current detector Cs is amplified by the differential amplifier AM1 and becomes the control voltage Va. The arithmetic unit AM2 calculates a voltage difference between the output Vb of the reference power source RP that generates a voltage corresponding to the maximum value of the current I and the output Va of the differential amplifier AM1.

The output signal Vc of the arithmetic unit AM2 is connected to the input of the voltage-current converter VIC. The voltage-current converter VIC connected in parallel with the capacitor C12 of the rectifying / smoothing circuit newly generates a current I2 proportional to the input voltage Vc in the line of the output voltage V2. As a result, the current I of the rectifying / smoothing circuit is the sum of the load current I1 and the current I2 of the voltage-current converter VIC.

FIG. 2 shows a circuit example of the voltage-current converter VIC. The input signal Vc is amplified by the amplifier AM3 and connected to the control terminal of the switching element Q12 and the source terminal of the switching element Q12 is connected to the current setting resistor R15. With this configuration, the current I2 flowing through the switching element Q12 is I2 = Vc / R5.

In the switching power supply configured as described above, an operation for reducing fluctuations in the output voltage of each power supply will be described with reference to FIG. As described in the conventional method, the voltage-current converter VIC is controlled so that I1min + I2 = I1max + I2 = a constant value even if the current I1 of the load LD1 changes from I1min to I1max. Here, it is the voltage drop of the current detector Cs that affects the control amount of the primary side switching element Q11. Since the current flowing through the rectifier diode D12 is constant, the forward voltage drop is constant. The reason why the variation ΔV3 occurs in the output voltage V3 is that the voltage drop of the current detector is different between I1min and I1max. In order to reduce the fluctuation amount of each output voltage, it is necessary to make the impedance of the current detector sufficiently small so that the fluctuation amount of the control amount of the primary side switching element Q11 becomes sufficiently small. The load current I1 can be detected by a current sensor using a magnetoresistive element in addition to the resistor.

The above process is expressed by the following equation.
Vc = Vb−Va Formula 3
Va = αI1 * r
Here, α is the amplification degree of the amplifier AM1, and r is the impedance of the current detector.
If Equation 3 is all proportional to current, it can be expressed by Equation 4.
I2 = Imax−I1 Formula 4
Therefore, the current I flowing through the output voltage V2 line always flows the maximum value Imax even if the current I1 flowing through the load LD1 fluctuates temporarily (instantaneously or transiently) or in the long term.

FIG. 3 shows this state. When the current I1 flowing through the load LD1 is the minimum I1min and the maximum I1max, the current I2 of Formula 4 is passed by the voltage-current converter VIC, and the current I is made constant so that the rectifier diode that has caused the output voltage fluctuation By eliminating the fluctuation of the forward voltage drop and further reducing the change in the on / off time ratio of the switching element Q11, the output voltage V3 becomes almost equal to ΔV3 and almost disappears. Similarly, the other output voltages V4 and V5 are not changed.
As described above, the output voltages V3 to V5 can output a voltage with little fluctuation. Accordingly, a dummy resistor for reducing voltage fluctuation that has been conventionally used is not required, and power consumption can be reduced and the apparatus can be downsized.
In the above embodiment, the configuration in the case where there is no common potential among the multiple outputs has been described. However, the circuit configuration in the case where a common potential is provided can be similarly realized.

  The present invention relates to a flyback type multi-output switching power supply, and can be applied to a control power supply used in various power supply devices, power conversion devices, electronic control devices, and the like.

V, DP: DC power supply T, T1: Transformers Q1, Q2, Q11: Switching element 21: Control circuits LD1-LD3, RL1, RL2: Load 11: PWM control circuit PD , PD11, photodiode Cs, current detector PT, PT11, phototransistor 32, dummy resistor circuits DM1-DM3, dummy resistor IC1, shunt regulators ZD1, ZD2, ZD3, ZD11 ... Zener diodes D1 to D3, D11 to D15 ... Diode RP ... Reference power supply VIC ... Voltage-current converter AM1, AM2 ... Amplifiers R1 to R8, R11 to R14 ... Resistor 11a ... Sub output circuits C1-C3, C12-C15 ... Capacitors 12 ... Main output circuit

Claims (4)

A transformer having a primary winding and a plurality of secondary windings; a switching element connected in series to the primary winding; and a control circuit for controlling an on-time width of the switching element to control an output voltage; A rectifying / smoothing circuit for rectifying and smoothing each output of the secondary winding, and a control signal for controlling the on-time width by detecting a voltage of one output as a reference voltage in the rectifying / smoothing circuit In a flyback type multi-output switching power supply device comprising an output voltage detection circuit for sending a feedback signal to the control circuit,
A variable current that controls the sum of the load current detector that detects the current flowing in the load connected to the reference output and the load current that is connected to the output of the rectifying and smoothing circuit to a constant current value. A flyback type multi-output switching power supply device comprising: a type dummy resistance circuit.   2. The flyback type multi-output switching power supply device according to claim 1, wherein the current variable type is configured so that a current value flowing through the rectifying / smoothing circuit of the reference output becomes a constant current value regardless of a change in load. A flyback type multi-output switching power supply device characterized by controlling a dummy resistor circuit.   3. The flyback type multi-output switching power supply device according to claim 1, wherein the constant current value flowing through the reference output rectifying and smoothing circuit is a maximum current value of a load. Type multi-output switching power supply. 4. The flyback type multi-output switching power supply device according to claim 1, wherein the current variable dummy resistance circuit includes a reference value provided in a control circuit, an output of the load current detector, and the like. A flyback type multi-output switching power supply device, characterized in that the flyback type multi-output switching power supply is a voltage-current converter controlled by a control amount generated on the basis of the deviation.