JP6621711B2 - Power switching circuit - Google Patents

Description

  The present invention relates to a power supply switching circuit for selectively switching between a first power supply and a second power supply having different output voltages.

  FIG. 4 is a circuit diagram showing a configuration of a conventional power supply switching circuit.

  The first primary-side input circuit 10 includes a first control circuit 11 that performs switching control for the first switching element Q1 and a series circuit of the primary winding N11 of the first transformer T1 and the first switching element Q1. Have. Similarly, the second primary side input circuit 20 performs a second control for performing a switching control on the series circuit of the primary winding N21 of the second transformer T2 and the second switching element Q2 and the second switching element Q2. A circuit 21 is included. The rectifying / smoothing circuit 30 constituting the first power supply E11 includes a rectifying diode D1 and a smoothing capacitor C1. The rectifying / smoothing circuit 50 constituting the second power supply E12 includes a rectifying diode D3 and a smoothing capacitor C3.

  The first feedback circuit 70a includes a shunt regulator SR1, resistance elements R2 to R5, and a photocoupler PC1. The second feedback circuit 90a includes a shunt regulator SR3, resistance elements R10 to R13, and a photocoupler PC2.

  The output voltage of the second power supply E12 is set higher than the output voltage of the first power supply E11. At normal times, the first power supply E11 set to a low output voltage is in a driving state, and the second power supply E12 set to a high output voltage is in a stopped state.

  In normal times, the output voltage of the first power supply E11 is output to the load circuit via the first backflow preventing diode D11 in the diode OR 60 '. The second diode D12 for preventing backflow in the diode OR performs backflow prevention for the output voltage of the first power supply E11. Due to the presence of the second backflow preventing diode D12, the output voltage of the first power supply E11 is not applied to the second power supply E12 in the stopped state.

  When the second power supply E12 is activated, the output voltage gradually increases with time. When the output voltage of the second power supply E12 exceeds the output voltage of the first power supply E11, the output voltage of the second power supply E12 instantly replaces the output voltage of the first power supply E11 to prevent the second backflow. It is output to the load circuit via the diode D12. The first backflow prevention diode D11 functions as a backflow prevention diode for the output voltage of the second power supply E12. Due to the presence of the first backflow preventing diode D11, the output voltage of the second power supply E12 is not applied to the first power supply E11.

  If there is no first backflow prevention diode D11, the output voltage of the second power supply E12 is applied to the first power supply E11, and the applied voltage is applied to the first feedback circuit 70a in the first power supply E11. Since the voltage is higher than the set voltage, the switching operation of the first switching element Q1 in the first primary side input circuit 10 is stopped, and the operation of the first power supply E11 is temporarily stopped in conjunction with the switching operation.

  By the way, it is desirable that the two-way switching between the output state of the first power supply E11 and the output state of the second power supply E12 with respect to the load circuit is performed instantaneously. Switching from the output voltage of the first power supply E11 to the output voltage of the second power supply E12 is instantaneously performed as described above.

  Here, when there is no first backflow prevention diode D11 and the output state of the first power supply E11 is temporarily stopped, thereafter, the output voltage of the second power supply E12 is lowered to reduce the first power supply. Consider a state in which the output voltage (specified value) of E11 has been reached. Since the voltage acting on the first feedback circuit 70a is lower than the set voltage, the switching operation of the first switching element Q1 in the first primary side input circuit 10 is restarted, and the first power supply E11 is activated to The output voltage starts to rise. However, switching from the second output voltage to the first output voltage is not executed unless the output voltage exceeds the output voltage of the second power supply E12 that is decreasing. That is, the output voltage to the load circuit falls below the set voltage [instantaneous switching failure (responsiveness defect) during power supply switching control].

  In order to avoid such a drop in the output voltage with respect to the load circuit, the output voltage of the second power source E12 is supplied to the first feedback circuit 70a by using the first backflow prevention diode D11 of the diode OR 60 '. The first power supply E11 is temporarily stopped from being applied, and the first feedback circuit 70a is maintained in an active state so that the output voltage of the first power supply E11 is maintained at a specified value. [Instantaneous switching during power switching control (high-speed response)].

  However, when the first backflow prevention diode D11 is used, the output current from the first power supply E11 is normally supplied to the load circuit via the first backflow prevention diode D11. 1 still has a problem that the power loss in the backflow prevention diode D11 becomes considerably large [power loss problem].

  That is, the power supply switching circuit of FIG. 4 has a power loss problem while ensuring high-speed response.

  As a proposed example for solving the above-mentioned problem recognized in FIG. 4, there is a power supply switching circuit having a circuit configuration shown in FIG. In the second conventional example, an auxiliary rectifying / smoothing circuit 40 is connected to the secondary winding N12 of the first transformer T1 in addition to the main rectifying / smoothing circuit 30, and the auxiliary rectifying / smoothing circuit 40 is connected to the feedback circuit. The power supply is 80a.

  The wired OR 60 at the junction of the output terminal of the first power supply E21 and the output terminal of the second power supply E22 connected to the load circuit is provided with a second diode D4 for backflow prevention. Those corresponding to the first backflow prevention diode D11 shown in FIG. 4 are omitted. By eliminating the first backflow prevention diode D11, loss of power supplied from the first power supply E21 to the load circuit in the normal state is reduced.

  Since the first backflow prevention diode D11 is eliminated, when the output voltage of the second power supply E22 is higher than the output voltage of the first power supply E21, the output voltage of the second power supply E22 is the first voltage. Is applied to the power source E21. However, the second output voltage is not applied to the auxiliary rectifying / smoothing circuit 40 due to the presence of the rectifying diode D1 interposed between the secondary winding N12 and the output terminal TO1. The voltage of the auxiliary rectifying / smoothing circuit 40 is monitored by a feedback circuit 80 a driven by the auxiliary rectifying / smoothing circuit 40. The switching operation of the first switching element Q1 of the first primary side input circuit 10 is controlled so that this voltage is maintained at a specified value. That is, when the power supply for supplying power to the load circuit is the second power supply E22, the first power supply E21 is also in the active state, and its output voltage is maintained at a voltage close to the specified value of the first power supply E21. The

  Therefore, the output voltage of the second power supply E22 is changed from the state in which the output voltage of the second power supply E22 is higher than the output voltage of the first power supply E21 and the output voltage of the second power supply E22 is supplied to the load circuit. When the power supply is switched to a state in which the power supply voltage is lower than the output voltage of the first power supply E21, the power supply for supplying power to the load circuit is immediately switched from the second power supply E22 to the first power supply E21, The power feeding operation is continued [instantaneous switching at the time of power switching control (high-speed response)].

  In addition, there is a technique disclosed in Patent Documents 1 and 2 as a conventional example that seems to have some relation.

JP 2012-151942 A JP-A-8-8073

  However, in the conventional power supply switching circuit shown in FIG. 5, the feedback circuit 80a is driven by the auxiliary rectifying and smoothing circuit 40, and the output voltage of the first power supply E21 that supplies power to the load circuit. It is not something to monitor. Although the output voltage of the auxiliary rectifying / smoothing circuit 40 is proportional to the output voltage of the main rectifying / smoothing circuit 30, it is not always equal. Rather, there is usually a difference between the two voltages. Therefore, as a result, the problem that the voltage accuracy of the output voltage of the first power supply E21 deteriorates cannot be avoided [voltage accuracy degradation].

  The present invention has been created in view of such circumstances, and the first power source side is a wired OR that commonly connects the output line of the first power source and the output line of the second power source to the load circuit. In the power supply switching circuit in which the first backflow prevention diode is omitted and the power loss is reduced, the instantaneous power supply switching control for switching the power supply for supplying power to the load circuit from the second power supply to the first power supply is provided. The object is to ensure switchability (high-speed response) and to increase the voltage accuracy of the output voltage of the first power supply.

  The present invention solves the above problems by taking the following measures.

The power supply switching circuit according to the present invention includes:
A control circuit for performing switching control on the switching element connected to the primary winding of the transformer;
A first power source configured by a main rectifying and smoothing circuit connected to the secondary winding of the transformer and capable of supplying a first voltage to a power output terminal;
A second power supply connected to the output line of the first power supply connected to the power supply output terminal via a wired OR connection via a backflow prevention diode and capable of supplying a second voltage to the power supply output terminal;
An auxiliary rectifying / smoothing circuit connected to the secondary winding of the transformer in a state of restricting current inflow from the second power supply via the backflow preventing diode;
A main feedback circuit for monitoring a change in the first voltage output from the main rectifying and smoothing circuit and feeding back to the control circuit;
An auxiliary feedback circuit for monitoring a change in the output voltage of the auxiliary rectifying and smoothing circuit and feeding back to the control circuit;
A voltage detection circuit that outputs a switching control signal based on a comparison result of voltage values of the first voltage and the second voltage;
The main feedback circuit is activated and the auxiliary feedback circuit is deactivated in the first mode in which the switching control signal by the voltage detection circuit is input and the second voltage is equal to or lower than the first voltage. And a feedback switching circuit that activates the auxiliary feedback circuit and deactivates the main feedback circuit when the second voltage exceeds the first voltage in the second mode. Features.

  In the power supply switching circuit of the present invention configured as described above, in the first mode in which the second voltage is equal to or lower than the first voltage, the higher first voltage is applied to the load circuit. The first voltage is not applied to the second power supply due to the presence of a diode for preventing backflow in the wired OR.

  In this first mode, the feedback switching circuit activates the main feedback circuit and deactivates the auxiliary feedback circuit. The main feedback circuit monitors the change in the first voltage output from the main rectifying / smoothing circuit and feeds it back to the control circuit. By this feedback control, the first power supply supplied to the load circuit is stabilized. Since the feedback control is performed by detecting the first voltage supplied to the load circuit, it is possible to ensure a high voltage accuracy of the first power supply.

  When the second voltage exceeds the first voltage due to the transition from the first mode, the higher second voltage is applied to the load circuit. The second voltage is applied to the first power supply via the wired OR (because the output line of the first power supply does not have a diode for preventing backflow in the wired OR). That is, it is applied to the main rectifying / smoothing circuit. However, it is not applied to the auxiliary rectifying / smoothing circuit. This is because, as described above, the auxiliary rectifying / smoothing circuit is connected to the secondary winding of the transformer in a state where current inflow from the second power supply is regulated.

  In this second mode, the feedback switching circuit activates the auxiliary feedback circuit and deactivates the main feedback circuit. The auxiliary feedback circuit monitors the change in the output voltage of the auxiliary rectifying and smoothing circuit and feeds it back to the control circuit. By this feedback control, the first power supply maintains its active state (the main rectifying / smoothing circuit and the auxiliary rectifying / smoothing circuit continue operating).

  Here, the feedback control is not based on the output voltage (first voltage) of the main rectifying / smoothing circuit outputting the first voltage, and is an auxiliary rectifying / smoothing that may have an error from the first voltage. Since it is based on the output voltage of the circuit, as a result, the voltage accuracy of the first voltage is degraded (voltage accuracy degradation).

  However, in the second mode, the second voltage is supplied to the load circuit, not the first voltage. Therefore, even if the voltage accuracy of the first voltage deteriorates in the second mode, it does not affect the voltage accuracy of the voltage supplied to the load circuit, and does not cause a problem.

  What is important here is that the diode for preventing the backflow is omitted from the output line of the first power source for power saving, so that the second voltage is the main rectifying and smoothing of the first power source in the second mode. It will be applied to the circuit (the first power supply will not cease operation), but it will not degrade the voltage accuracy of the supply voltage to the load circuit.

  Next, when returning from the second mode to the first mode, this time, the voltage control circuit switching control signal deactivates the auxiliary feedback circuit and activates the main feedback circuit via the feedback switching circuit. To do. Here, since the auxiliary rectifying / smoothing circuit and the main rectifying / smoothing circuit are kept active immediately before, the first voltage from the main rectifying / smoothing circuit is changed from the second mode to the first mode. A high-precision voltage is obtained at a predetermined level from the moment of switching. That is, it is possible to ensure instantaneous switchability (high-speed response) during power supply switching control.

  The power supply switching circuit of the present invention having the above-described configuration has several preferred modes, variations and modifications as follows.

  [1] A change in the second voltage output from the second power source is monitored, and a voltage value corresponding to the second voltage is determined by comparing the predetermined voltage with a predetermined value set in advance. The switch control signal for switching to the first mode is output when the value is equal to or less than the value, and the switch control signal for switching to the second mode when the voltage value corresponding to the second voltage exceeds the specified value. Is output. If comprised in this way, a 1st mode and a 2nd mode can be switched easily by comparing the predetermined value and the 2nd voltage which were preset.

  [2] Further, there is a mode in which the main feedback circuit and the auxiliary feedback circuit are diode-or connected. With this configuration, the signal output destination of the main feedback circuit and the signal output destination of the auxiliary feedback circuit can be combined on a common line while avoiding mutual buffering, which is advantageous in simplifying the circuit configuration.

  [3] The main rectifying / smoothing circuit includes a rectifying diode, and the rectifying diode rectifies an AC voltage induced in the transformer output and regulates an inflow of current from the second power source. There is an aspect of being configured. By giving two functions to one rectifier diode, it is advantageous to simplify the circuit configuration.

  The voltage detection circuit can be composed of a shunt regulator and a comparator.

  In addition, the feedback switching circuit can be configured with a switching element, a unidirectional energization element, and the like.

  According to the present invention, power supply switching is performed by reducing the power loss by omitting the first backflow prevention diode on the first power supply side by wired OR to the load circuit of the first power supply and the second power supply. In the circuit, the voltage accuracy of the output voltage of the first power supply is ensured while ensuring the instantaneous switchability (high-speed response) at the time of power supply switching control for switching the power supply for supplying power to the load circuit from the second power supply to the first power supply. Can be expensive.

The circuit diagram which shows the structure of the power supply switching circuit in the Example of this invention Operational state diagram of the first mode of the power supply switching circuit in the embodiment of the present invention Operational state diagram of the second mode of the power supply switching circuit in the embodiment of the present invention 1 is a circuit diagram showing a configuration of a power supply switching circuit of a first conventional example The circuit diagram which shows the structure of the power supply switching circuit of a 2nd prior art example

  Hereinafter, the embodiment of the power supply switching circuit of the present invention having the above configuration will be described in detail at the level of specific examples.

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

  In FIG. 1, 10 is a first primary side input circuit, 20 is a second primary side input circuit, 30 is a main rectifying and smoothing circuit constituting the first power source E1, 40 is an auxiliary rectifying and smoothing circuit, and 50 is The rectifying / smoothing circuit constituting the second power source E2, 60 is a wired OR, 70 is a main feedback circuit, 80 is an auxiliary feedback circuit, 90 is a high voltage side feedback circuit, 100 is a diode OR, 110 is a voltage detection circuit , 120 are feedback switching circuits. T11 and T12 are DC input terminals of the first primary side input circuit 10, T21 and T22 are DC input terminals of the second primary side input circuit 20, TO1 is a power supply output terminal, TO2 is a ground terminal, and T1 is a first input terminal. 1 transformer, T2 is a second transformer, PC1 is a first photocoupler, and PC2 is a second photocoupler.

  The first primary side input circuit 10 includes a primary winding N11 of a first transformer T1, a first switching element Q1, and a first control circuit 11. A series circuit of a primary winding N11 and a first switching element Q1 is connected between positive and negative DC input terminals T11, T12 of the first primary side input circuit 10. The switching operation of the first switching element Q1 is controlled by the first control circuit 11. An alternating voltage is induced in the secondary winding N12 of the first transformer T1 by the switching operation of the first switching element Q1. The first control circuit 11 is configured to stop the switching control for the first switching element Q1 by a control signal when the light receiving element RE1 of the first photocoupler PC1 (for feedback control) is turned on.

  The second primary side input circuit 20 includes a primary winding N21 of the second transformer T2, a second switching element Q2, and a second control circuit 21. A series circuit of a primary winding N21 and a second switching element Q2 is connected between positive and negative DC input terminals T21 and T22 of the second primary side input circuit 20. The switching operation of the second switching element Q2 is controlled by the second control circuit 21. An alternating voltage is induced in the secondary winding N22 of the second transformer T2 by the switching operation of the second switching element Q2. The second control circuit 21 is configured to stop the switching control for the second switching element Q2 by a control signal when the light receiving element RE2 of the second photocoupler PC2 (for feedback control) is turned on.

  The first and second switching elements Q1 and Q2 are composed of, for example, FETs (field effect transistors), and N-channel type MOSFETs are employed here. The light receiving elements RE1 and RE2 in the first and second photocouplers PC1 and PC2 are configured by, for example, phototransistors, and the corresponding light emitting elements EE1 and EE2 are configured by, for example, light emitting diodes (LEDs).

  The main rectifying / smoothing circuit 30 in the first power supply E1 includes a rectifying diode D1 and a smoothing capacitor C1. A series circuit of a rectifier diode D1 and a smoothing capacitor C1 is connected between both ends of the secondary winding N12 of the first transformer T1, and a main rectification smoothing circuit 30 is configured. The connection point between the cathode of the rectifier diode D1 and the positive terminal of the smoothing capacitor C1 constitutes the output point of the main rectifying and smoothing circuit 30, and this output point is connected to the power supply output terminal TO1 via the first output line L1. ing. A negative terminal of a load circuit (not shown) whose positive terminal is connected to the power output terminal TO1 is connected to the ground terminal TO2, and the ground terminal TO2 is a return terminal of the main rectifying and smoothing circuit 30 via the first ground line GL1. It is connected to the.

  In addition to the main rectifying / smoothing circuit 30 described above, a series circuit of a rectifying diode D2, a resistor element R1, and a smoothing capacitor C2 is connected between both ends of the secondary winding N12 of the first transformer T1, thereby providing an auxiliary rectifying / smoothing circuit. 40 is configured. A connection point between the resistance element R1 connected to the cathode of the rectifier diode D2 and the positive terminal of the smoothing capacitor C2 constitutes an output point of the auxiliary rectification smoothing circuit 40. This output point has a circuit configuration separated from the power supply output terminal TO1 (first output line L1).

  The rectifying / smoothing circuit 50 on the high voltage side in the second power supply E2 includes a rectifying diode D3 and a smoothing capacitor C3. A series circuit of a rectifier diode D3 and a smoothing capacitor C3 is connected between both ends of the secondary winding N22 of the second transformer T2, and a rectifying and smoothing circuit 50 on the high voltage side is configured. The connection point between the cathode of the rectifying diode D3 and the positive terminal of the smoothing capacitor C3 constitutes the output point of the rectifying / smoothing circuit 50 on the high voltage side, and this output point forms the second output line L2 and the diode D4 for preventing backflow. To the power output terminal TO1. A ground terminal TO2 to which a negative terminal of a load circuit (not shown) is connected is connected to a return terminal of the rectifying / smoothing circuit 50 on the high voltage side via a second ground line GL2.

  The main rectifying / smoothing circuit 30 and the first output line L1 constitute the first power supply E1, and the high-voltage side rectifying / smoothing circuit 50, the second output line L2, and the backflow preventing diode D4 are the second power supply. E2 is configured. The first output line L1 and the second output line L2 form a wired OR 60 with respect to the power supply output terminal TO1, and in this wired OR 60, the backflow prevention diode D4 is connected to the second output line L2. Although inserted, no diode for preventing backflow is inserted in the first output line L1.

  The rectifying / smoothing circuit 50 in the second power source E2 has a modifier “on the high voltage side”, which is higher than the voltage generated by the main rectifying / smoothing circuit 30 in the first power source E1. Is not necessarily necessarily higher than the generated voltage of the main rectifying / smoothing circuit 30. There is also a mode (first mode) in which the generated voltage of the rectifying and smoothing circuit 50 on the high voltage side is lower than the generated voltage of the main rectifying and smoothing circuit 30. The modifier “on the high voltage side” is used only to distinguish the modifiers “main” and “auxiliary” in the first power supply E1.

  The main feedback circuit 70 in the first power supply E1 includes a shunt regulator SR1, a backflow prevention diode D5, resistance elements R2 to R5, and a first photocoupler PC1. A series circuit of resistance elements R2 and R3 is connected between the output terminals of the main rectifying and smoothing circuit 30 (between both ends of the smoothing capacitor C1). A series circuit of resistance elements R4 and R5 and a shunt regulator SR1 is connected between the output terminals of the main rectifying and smoothing circuit 30. The shunt regulator SR1 has an anode connected to the negative terminal of the smoothing capacitor C1, and a cathode connected to the resistance element R5. A resistance element R4 connected to the resistance element R5 is connected to the first output line L1. The reference terminal of the shunt regulator SR1 is connected to the connection point of the resistance elements R2 and R3. A series circuit of a diode D5 for preventing backflow and a light emitting element EE1 in the first photocoupler PC1 is connected between both ends of the resistor element R5.

  The auxiliary feedback circuit 80 in the first power supply E1 includes a shunt regulator SR2, a backflow prevention diode D6, resistance elements R6 to R9, and the first photocoupler PC1. The first photocoupler PC1 is shared with the main feedback circuit 70. A series circuit of resistance elements R6 and R7 is connected between the output terminals of the auxiliary rectifying and smoothing circuit 40 (between both ends of the smoothing capacitor C2). A series circuit of resistance elements R8, R9 and a shunt regulator SR2 is connected between the output terminals of the auxiliary rectifying / smoothing circuit 40. Shunt regulator SR2 has its anode connected to the negative terminal of smoothing capacitor C2 and its cathode connected to resistance element R9. A resistance element R8 connected to the resistance element R9 is connected to the positive terminal of the smoothing capacitor C2. The reference terminal of the shunt regulator SR2 is connected to the connection point of the resistance elements R6 and R7. A series circuit of a backflow preventing diode D6 and a light emitting element EE1 in the first photocoupler PC1 is connected between both ends of the resistor element R9.

  The backflow prevention diode D5 in the main feedback circuit 70 and the backflow prevention diode D6 in the auxiliary feedback circuit 80 constitute a diode OR 100 with respect to the light emitting element EE1 of the first photocoupler PC1.

  The light receiving element RE1 in the first photocoupler PC1 is connected to the first control circuit 11. When the feedback signal of the optical signal when the light emitting element EE1 is operated is incident on the light receiving element RE1 and the light receiving element RE1 is turned on, the switching operation for the first switching element Q1 by the first control circuit 11 is stopped. ing.

  The high voltage side feedback circuit 90 in the second power source E2 includes a shunt regulator SR3, resistance elements R10 to R13, and a second photocoupler PC2. A series circuit of resistance elements R10 and R11 is connected between the output terminals of the rectifying and smoothing circuit 50 on the high voltage side (between both ends of the smoothing capacitor C3). Further, a series circuit of resistance elements R12 and R13 and a shunt regulator SR3 is connected between the output terminals of the rectifying and smoothing circuit 50 on the high voltage side. Shunt regulator SR3 has its anode connected to the negative terminal of smoothing capacitor C3 and its cathode connected to resistance element R13. A resistance element R12 connected to the resistance element R13 is connected to the second output line L2. The reference terminal of the shunt regulator SR3 is connected to the connection point of the resistance elements R10 and R11. The light emitting element EE2 in the second photocoupler PC2 is connected between both ends of the resistor element R13.

  The light receiving element RE2 in the second photocoupler PC2 is connected to the second control circuit 21. When the feedback signal of the optical signal when the light emitting element EE2 is operated is incident on the light receiving element RE2 and the light receiving element RE2 is turned on, the switching operation for the second switching element Q2 by the second control circuit 21 is stopped. ing.

  The voltage detection circuit 110 includes a shunt regulator SR4, a comparator Cm, and resistance elements R14 to R18. The shunt regulator SR4 has an anode connected to the second ground line GL2, and a cathode connected to the second output line L2 via the resistance element R14. The reference terminal is connected (short-circuited) to the cathode. The cathode of the shunt regulator SR4 is connected to the second ground line GL2 via a series circuit of two resistance elements R15 and R16. The comparator Cm has its inverting input terminal (−) connected to the connection point of the series resistance elements R15 and R16, and its non-inverting input terminal (+) between the second output line L2 and the ground line GL2. It is connected to the connection point of the connected series resistance elements R17 and R18. A voltage proportional to the output voltage of the second power supply E2 is input to the non-inverting input terminal (+).

The reference voltage of the shunt regulator SR4 is the resistance element R15, R16
And is input as a reference voltage to the inverting input terminal (−) of the comparator Cm. Further, a voltage obtained by resistance-dividing the output voltage of the second power supply E2 by the series resistance elements R18 and R17 is input as a detection voltage to the non-inverting input terminal (+) of the comparator Cm. When the output voltage of the second power source E2 is lower than a predetermined specified value (hereinafter simply referred to as “specified value”) set in advance (the detection voltage by resistance division is lower than the reference voltage), the comparator Cm When the switching control signal Sc at the “L” level is output from the terminal and the second output voltage becomes equal to or higher than the specified value, the switching control signal Sc is switched to the “H” level.

  The feedback switching circuit 120 includes switching elements Q3 and Q4, backflow prevention diodes D7 and D8, and resistance elements R19 to R23. The switching elements Q3 and Q4 are bipolar and NPN transistors. The base (control terminal) of the switching element Q3 is connected to the output terminal of the comparator Cm in the voltage detection circuit 110 via the resistance element R19. A connection point between the resistor element R19 and the base is connected to the first ground line GL1 via the resistor element R20.

  The emitter of the switching element Q3 is connected to the first ground line GL1, and the collector thereof is connected to the connection point of the resistance elements R2 and R3 in the main feedback circuit 70 via the rectifier diode D7. The rectifier diode D7 has an anode connected to the resistance elements R2 and R3, and a cathode connected to the collector of the switching element Q3.

  The collector of the switching element Q3 is connected to the output side (the positive terminal of the smoothing capacitor C2) of the auxiliary rectifying / smoothing circuit 40 through a series circuit of the rectifying diode D8 and the resistor element R21. The rectifier diode D8 has an anode connected to the connection point of the resistance elements R21 and R22, and a cathode connected to the collector of the switching element Q3.

  A series circuit of resistance elements R22 and R23 is connected between a connection point between the anode of the rectifier diode D8 and the resistance element R21 and the first ground line GL1. The base (control terminal) of the switching element Q4 is connected to the connection point of the resistance elements R22 and R23, the emitter is connected to the first ground line GL1, and the collector is the series resistance element R6 in the auxiliary feedback circuit 80. It is connected to the connection point of R7.

  As described above, in this embodiment, the first power supply E1 includes the auxiliary feedback circuit 80 in addition to the main feedback circuit 70, and further includes the voltage detection circuit 110 and the feedback switching circuit 120. Further, the main feedback circuit 70 and the auxiliary feedback circuit 80 are coupled with a diode OR 100 and are commonly connected to the light emitting element EE1 of the first photocoupler PC1.

  If the output voltage of the second power supply E2 being monitored is equal to or lower than the specified value, the voltage detection circuit 110 is lower than the voltage reference voltage applied to the non-inverting input terminal (+) of the comparator Cm. The output signal from the signal becomes “L” level.

  Next, the operation of the power supply switching circuit of the present embodiment configured as described above will be described.

  (1) First, the operation in the first mode in which the output voltage of the second power supply E2 is not more than the specified value will be described with reference to FIG.

  In FIG. 2, an element surrounded by a bold circle mark means that the element is in a conductive state (active state), and an element marked with a shape with a diagonal line / added to the bold circle mark in a non-conductive state ( Inactive state).

  When the output voltage of the second power supply E2 is equal to or lower than the specified value, the voltage applied to the non-inverting input terminal (+) of the comparator Cm is lower than the reference voltage, and therefore the switching control signal Sc output from the comparator Cm is “ L "level. As a result, the switching element Q3 in the feedback switching circuit 120 remains in a non-conductive state, and the switching element Q4 is in a conductive state in conjunction therewith.

  Since the switching element Q3 is non-conductive, the shunt regulator SR1 of the main feedback circuit 70 in the first power supply E1 is conductive because the feedback voltage to the reference terminal is higher than the reference voltage. On the other hand, since the switching element Q4 is in a conductive state, the shunt regulator SR2 of the auxiliary feedback circuit 80 in the first power supply E1 is in a nonconductive state because the feedback voltage to the reference terminal is equal to or lower than the reference voltage. .

  That is, when the output voltage of the second power supply E2 is equal to or lower than the specified value, the main feedback circuit 70 is in an active state, whereas the auxiliary feedback circuit 80 is in an inactive state.

  When the output voltage of the first power supply E1 is higher than the output voltage of the second power supply E2, the higher first power supply E1 is present due to the presence of the backflow prevention diode D4 on the second power supply E2 side in the wired OR 60. Is not applied to the second power supply E2 side. In the first mode, the output voltage from the first power supply E1 is output to the load circuit. That is, the output current for the load circuit is supplied from the first power supply E1. Then, feedback control is performed by the control circuit 11 by the function of the main feedback circuit 70 in the active state, and the output voltage of the first power supply E1 is maintained at a constant value.

  Even if the output voltage of the first power supply E1 is higher than the output voltage of the second power supply E2, the backflow prevention diode D4 on the second power supply E2 side exists in the wired OR 60. The output voltage of the first power supply E1 is not applied to the second power supply E2 side. That is, no adverse effect is caused by the omission of the backflow prevention diode (see D11 in FIG. 4) on the first power supply E1 side in the wired OR 60.

  The output voltage of the second power supply E2 is feedback-controlled by the control circuit 11 by the function of the feedback circuit 90 on the high voltage side of the second power supply E2, and is kept at a constant value.

  (2) Next, the operation in the second mode in which the output voltage of the second power source E2 exceeds the specified value will be described with reference to FIG.

  In FIG. 3, the element surrounded by a thick circle ○ means that the element is in a conductive state (active state), and the element marked with a hatched line / in the thick line ○ is in a non-conductive state ( Inactive state).

  When the output voltage of the second power supply E2 exceeds the specified value, the voltage applied to the non-inverting input terminal (+) of the comparator Cm is higher than the reference voltage, so that the switching control signal Sc output from the comparator Cm is inverted. Then, it becomes “H” level. As a result, the switching element Q3 in the feedback switching circuit 120 is inverted and made conductive, and the switching element Q4 is inverted and becomes non-conductive.

  The switching element Q3 becomes conductive, and the shunt regulator SR1 of the main feedback circuit 70 in the first power supply E1 is inverted and becomes non-conductive. On the other hand, the switching element Q4 is inverted and becomes non-conductive, and the shunt regulator SR2 of the auxiliary feedback circuit 80 in the first power supply E1 is inverted and becomes conductive.

  That is, when the output voltage of the second power supply E2 exceeds a specified value, the auxiliary feedback circuit 80 is activated, whereas the main feedback circuit 70 is deactivated.

  When the output voltage of the second power source E2 is higher than the output voltage of the first power source E1, the output voltage of the higher second power source E2 is applied to the first power source E1 having the lower voltage. The This is because there is no backflow prevention diode (corresponding to D11 in FIG. 4) on the first power source E1 side in the wired OR 60. In the second mode, the output voltage from the second power supply E2 is output to the load circuit. That is, the output current for the load circuit is supplied from the second power supply E2. Then, by the function of the auxiliary feedback circuit 80 in the active state, the switching operation is performed by applying the output voltage of the second power source E2 higher than the output voltage of the first power source E1 to the first power source E1 side. Stopping can be prevented. As described above, the feedback is performed by the auxiliary feedback circuit 80 instead of the main feedback circuit 70 when the output voltage of the second power supply E2 is higher than the output voltage of the first power supply E1. This is because the circuit 70 is affected by the output voltage of the second power supply E2, and the switching of the first power supply E1 is stopped. When the switching is stopped, the first power supply E1 once stops its operation. Therefore, even if the output voltage of the second power supply E2 decreases in this state, the first power supply E1 does not immediately start up. Depressed greatly. As in this embodiment, switching is performed by feedback of the auxiliary feedback circuit 80, so that the power supply is not supplied to the load, but the first power supply E1 itself is operating. Therefore, the output voltage of the second power supply E2 is Even if the voltage drops, the voltage is immediately output from the first power supply E1, and the drop of the output voltage can be prevented. In this second mode, the high output voltage of the second power supply E2 is applied to the first power supply E1, but the feedback function for voltage control in the first power supply E1 is an auxiliary The rectifying / smoothing circuit 40 is configured to perform the auxiliary feedback circuit 80.

  In this auxiliary rectifying / smoothing circuit 40, since the current inflow from the second power source E2 is restricted by the presence of the rectifying diode D1 in the main rectifying / smoothing circuit 30, the output voltage of the second power source E2 is the first voltage. Even if the power source E1 is affected, the auxiliary rectifying / smoothing circuit 40 is not affected by the output voltage of the second power source E2. Therefore, the output voltage of the second power supply E2 is applied to the first power supply E1 as a result of removing the backflow prevention diode on the first power supply E1 side in the wired OR 60 immediately before the power supply output terminal TO1. However, the voltage control in the first power source E1 is performed substantially as expected.

  That is, when the output voltage of the second power supply E2 is higher than the output voltage of the first power supply E1, the backflow prevention diode on the first power supply E1 side is omitted in the wired OR 60. Even if the output voltage of the higher second power supply E2 is applied to the first power supply E1 side, the voltage fluctuation of the first power supply E1 is fed back because of the influence of the output voltage of the second power supply E2. Since the auxiliary feedback circuit 80 is not affected by the output voltage of the second power supply E2 instead of the main feedback circuit 70 to be received, the backflow prevention diode on the first power supply E1 side is omitted in the wired OR 60 after all. There will be no harmful effects caused by this. Note that the output voltage of the second power source E2 is maintained at a constant value by the function of the feedback circuit 90 on the high voltage side of the second power source E2, as in the case of (1) above.

  According to the present invention, the first backflow prevention diode on the first power supply side is omitted by a wired OR that commonly connects the output line of the first power supply and the output line of the second power supply to the load circuit. With regard to the power supply switching circuit designed to reduce power loss, after ensuring the instantaneous switchability (high-speed responsiveness) at the time of power supply switching control for switching the power supply to the load circuit from the second power supply to the first power supply This is useful as a technique for increasing the voltage accuracy of the output voltage of the first power supply.

DESCRIPTION OF SYMBOLS 11 Control circuit 30 Main rectification smoothing circuit 40 Auxiliary rectification smoothing circuit 60 Wired OR 70 Main feedback circuit 80 Auxiliary feedback circuit 100 Diode OR 110 Voltage detection circuit 120 Feedback switching circuit Cm Comparator D1 Rectifier diode D4 Diode for backflow prevention D7, D8 Unidirectional energization element E1 First power supply E2 Second power supply L1 Output line of first power supply L2 Output line of second power supply N11 Primary winding N12 Secondary winding Q1 Switching element Q3, Q4 Feedback Switching element of switching circuit Sc Switching control signal SR4 Shunt regulator of voltage detection circuit T1 Transformer TO1 Power supply output terminal

Claims (6)

A control circuit for performing switching control on the switching element connected to the primary winding of the transformer;
A first power source configured by a main rectifying and smoothing circuit connected to the secondary winding of the transformer and capable of supplying a first voltage to a power output terminal;
A second power supply connected to the output line of the first power supply connected to the power supply output terminal via a wired OR connection via a backflow prevention diode and capable of supplying a second voltage to the power supply output terminal;
An auxiliary rectifying / smoothing circuit connected to the secondary winding of the transformer in a state of restricting current inflow from the second power supply via the backflow preventing diode;
A main feedback circuit for monitoring a change in the first voltage output from the main rectifying and smoothing circuit and feeding back to the control circuit;
An auxiliary feedback circuit for monitoring a change in the output voltage of the auxiliary rectifying and smoothing circuit and feeding back to the control circuit;
A voltage detection circuit that outputs a switching control signal based on a comparison result of voltage values of the first voltage and the second voltage;
The main feedback circuit is activated and the auxiliary feedback circuit is deactivated in the first mode in which the switching control signal by the voltage detection circuit is input and the second voltage is equal to or lower than the first voltage. And a feedback switching circuit that activates the auxiliary feedback circuit and deactivates the main feedback circuit when the second voltage exceeds the first voltage in the second mode. A characteristic power supply switching circuit. The voltage detection circuit is
The change in the second voltage output from the second power source is monitored, and a voltage value corresponding to the second voltage is equal to or less than the specified value by comparing with a predetermined specified value set in advance. The switching control signal for switching to the first mode is output when the switching control signal for switching to the second mode is output when the voltage value corresponding to the second voltage exceeds the specified value. The power supply switching circuit according to claim 1.   The power supply switching circuit according to claim 1, wherein the main feedback circuit and the auxiliary feedback circuit are diode-or connected.   The main rectifying / smoothing circuit includes a rectifying diode, and the rectifying diode rectifies an AC voltage induced in the transformer output and is configured to restrict current inflow from the second power supply. The power supply switching circuit according to any one of claims 1 to 3.   The power supply switching circuit according to any one of claims 1 to 4, wherein the voltage detection circuit includes a shunt regulator and a comparator.   The power supply switching circuit according to any one of claims 1 to 5, wherein the feedback switching circuit includes a switching element and a unidirectional energization element.

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