JP6635513B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply including a PFC circuit and a DC / DC converter circuit.

  As a switching power supply device provided with a PFC circuit and a DC / DC converter circuit, for example, a switching power supply device described in Patent Document 1 is known. As shown in FIG. 4, the switching power supply device 11 described in Patent Document 1 includes a PFC circuit 12, a DC / DC converter circuit 13, an auxiliary power supply circuit 14, an overcurrent point shift circuit 15, a first control circuit 16 and a second control circuit 17.

  The first control circuit 16 stops the switching operation of the switch Q1 of the PFC circuit 12 in the light load mode (when the PFC signal is at a low level), and in the heavy load mode (when the PFC signal is at a high level). , The switching operation of the switch Q1 of the PFC circuit 12 is executed. Thus, the PFC circuit 12 performs the power factor improving operation only in the heavy load mode.

  Further, the first control circuit 16 has a first terminal connected to the current path of the switch Q2 of the DC / DC converter circuit 13, and a voltage input to the first terminal (hereinafter, a first terminal voltage) is applied. When the voltage is equal to or less than the predetermined threshold, the switching operation of the switch Q2 is executed. On the other hand, when the first terminal voltage exceeds the predetermined threshold, the switching operation of the switch Q2 is stopped as an overcurrent protection operation.

  The overcurrent point shift circuit 15 includes a series circuit including a resistor R14 and a switch Q3, which is connected in parallel to the current detection resistor R11 of the DC / DC converter circuit 13. The overcurrent point shift circuit 15 turns off the switch Q3 to disconnect the resistor R14 from the resistor R11 in the light load mode, and turns on the switch Q3 to turn on the resistor R11 in the heavy load mode. To be connected in parallel.

  The combined resistance value when the resistor R14 is connected in parallel to the resistor R11 is smaller than the resistance value when the resistor R11 is used alone. For this reason, in order for the first terminal voltage to exceed the predetermined threshold, more current is required in the heavy load mode than in the light load mode. In other words, the overcurrent point in the heavy load mode (the current value of the current flowing through the switch Q2 when the first terminal voltage exceeds the predetermined threshold) is larger than the overcurrent point in the light load mode. Therefore, in the switching power supply 11, the overcurrent point can be changed to an appropriate value according to the load mode.

JP-A-2015-126638

  As described above, the conventional switching power supply device 11 can change the overcurrent point to an appropriate value by switching on / off the switch Q3 according to the load mode. However, the conventional switching power supply device 11 has a problem in that the component cost increases due to the switch Q3.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching device capable of changing an overcurrent point to an appropriate value according to a load mode without increasing a component cost. A power supply device is provided.

In order to solve the above-described problems, a switching power supply according to the present invention includes:
A PFC circuit that includes a first switch and converts an input voltage to a first DC voltage while improving a power factor by a switching operation of the first switch;
A DC / DC converter circuit that includes a second switch and converts the first DC voltage into a second DC voltage by a switching operation of the second switch;
A switching power supply for supplying the second DC voltage to a load,
A PFC signal and an overcurrent signal are input, and the switching operation of the first switch is executed / stopped according to the input / non-input of the PFC signal, while the second operation is performed according to the input / non-input of the overcurrent signal. A control circuit for stopping / executing the switching operation of the switch;
An overcurrent signal output circuit that outputs the overcurrent signal to the control circuit;
With
The overcurrent signal output circuit,
A selection circuit to which the second DC voltage and the voltage of the PFC signal are input and that outputs a larger one of a second voltage proportional to the second DC voltage or a third voltage proportional to the voltage of the PFC signal When,
A voltage generation circuit that generates a first voltage proportional to an output current supplied to the load;
Comparing the second voltage or the third voltage input from the selection circuit with the first voltage, and when the first voltage is higher than the second voltage or the third voltage, the overcurrent signal; And a comparison circuit that outputs

  According to this configuration, unlike the conventional switching power supply device, a switch (switch Q3 of the switching power supply device 11) that switches on / off according to the load mode, that is, input / non-input of the PFC signal, becomes unnecessary, and thus the components are not required. The overcurrent point can be changed to an appropriate value according to the load mode without increasing the cost.

In the switching power supply device, for example,
The voltage generation circuit includes a resistor that detects the output current,
The selection circuit includes an OR circuit including a first diode and a second diode for outputting a larger one of the second voltage and the third voltage,
The comparison circuit has a first input terminal to which the second voltage or the third voltage is input, a second input terminal to which the first voltage is input, and an output terminal that outputs the overcurrent signal. A configuration including an operational amplifier can be employed.

  According to the present invention, it is possible to provide a switching power supply device capable of changing an overcurrent point to an appropriate value according to a load mode without increasing component costs.

1 is a circuit diagram of a switching power supply according to the present invention. FIG. 4 is a diagram for explaining an overcurrent protection operation in the present invention. (A) is a diagram for explaining an overcurrent point P1 in a light load mode (when a PFC signal is not input). (B) is a diagram for explaining an overcurrent point P2 in a heavy load mode (when a PFC signal is input). FIG. 10 is a circuit diagram of a conventional switching power supply device.

  Hereinafter, an embodiment of a switching power supply according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a switching power supply device 1 according to an embodiment of the present invention. The switching power supply 1 includes a high-potential-side input terminal T1, a low-potential-side input terminal T1 ', a high-potential-side output terminal T2, a low-potential-side output terminal T2', and a PFC signal input terminal T3. And An AC power supply is connected to the input terminals T1 and T1 ', and a load (not shown) is connected to the output terminals T2 and T2'.

  A predetermined PFC signal is input to the PFC signal input terminal T3. In the switching power supply device 1, when the PFC signal is input (for example, when the PFC signal is at a high level), the switching power supply device 1 is in the heavy load mode. Mode.

  The switching power supply device 1 includes a full-wave rectifier circuit D1, a PFC circuit 2, a DC / DC converter circuit 3, an auxiliary power supply circuit 4, an overcurrent signal output circuit 5, a first control circuit 6, and a second control circuit. A circuit 7 and first to third signal transmission means PC1 to PC3 are provided.

  The PFC circuit 2 is connected to input terminals T1 and T1 'via a full-wave rectifier circuit D1 composed of a diode bridge. The PFC circuit 2 includes a boost chopper circuit including a choke coil L1, a switch (for example, a transistor) Q1 corresponding to the “first switch” of the present invention, a diode D2, and a capacitor C1. When the switch Q1 is performing a switching operation (when performing a power factor improvement operation), the PFC circuit 2 outputs a first DC voltage substantially equal to the peak value of the input voltage, and the switch Q1 performs the switching operation. When the operation is stopped (when the power factor improvement operation is not performed), the first DC voltage higher than the peak value of the input voltage is output.

  The DC / DC converter circuit 3 includes a switch (for example, a transistor) Q2 corresponding to the “second switch” of the present invention, a primary winding N1 and a secondary winding N2 of the transformer TR1, a diode D3, and a capacitor C2. It consists of. One end of the primary winding N1 is connected to one end of the capacitor C1 of the PFC circuit 2, and the other end is connected to GND via the switch Q2. The secondary winding N2 has a reverse polarity relationship with the primary winding N1, one end is connected to the output end T2 via the diode D3 and the overcurrent signal output circuit 5, and the other end is connected to GND. . The capacitor C2 has one end connected to the cathode of the diode D3 and the other end connected to GND. The DC / DC converter circuit 3 converts the first DC voltage into a second DC voltage by the switching operation of the switch Q2 and outputs the second DC voltage.

  The auxiliary power supply circuit 4 includes a tertiary winding N3 of the transformer TR1, a diode D4, and a capacitor C3. The auxiliary power supply circuit 4 converts the AC voltage generated in the tertiary winding N3 into a DC voltage by the diode D4 and the capacitor C3, and outputs the DC voltage as a power supply voltage of the first control circuit 6.

  The overcurrent signal output circuit 5 includes a first voltage dividing circuit including a resistor R1 and a resistor R2, a diode D5 corresponding to a “first diode” of the present invention, and a diode corresponding to a “second diode” of the present invention. An OR circuit including D6, a second voltage dividing circuit including resistors R3 and R4, a resistor R5, and an operational amplifier OP1. The resistors R1 to R4 and the diodes D5 and D6 correspond to a “selection circuit” of the present invention. The resistor R5 corresponds to the “voltage generating circuit” of the present invention. The operational amplifier OP1 corresponds to the “comparing circuit” of the present invention.

  In the first voltage dividing circuit, one end (one end of the resistor R1) is connected to the output end T2, and the other end (the other end of the resistor R2) is connected to GND. In the OR circuit, the anode of the diode D5 is connected to the voltage dividing point of the first voltage dividing circuit, the cathode of the diode D5 is connected to the cathode of the diode D6, and the anode of the diode D6 is connected to the PFC signal input terminal T3. I have. In the second voltage dividing circuit, one end (one end of the resistor R3) is connected to the cathodes of the diodes D5 and D6, and the other end (the other end of the resistor R4) is connected to GND.

  The resistor R5 has one end connected to the other end of the second voltage dividing circuit (the other end of the resistor R4) and GND, and the other end connected to the output end T2 '. The output current supplied to the load flows through the resistor R5. Therefore, the resistor R5 can generate a voltage proportional to the output current (the “first voltage” of the present invention).

  The operational amplifier OP1 has an inverting input terminal corresponding to the “first input terminal” of the present invention connected to the voltage dividing point of the second voltage dividing circuit, and the “second input terminal” of the present invention connected to the other end of the resistor R5. It has a non-inverting input terminal corresponding to the “input terminal”, and an output terminal connected to the light emitting element of the third signal transmission means (photocoupler in this embodiment) PC3 via the resistor R7.

  In the overcurrent signal output circuit 5, while the divided voltage obtained by dividing the second DC voltage by the first voltage dividing circuit is inputted to the anode of the diode D5, the voltage of the PFC signal is inputted to the anode of the diode D6. You. When the divided voltage is larger than the voltage of the PFC signal, the divided voltage is output from the OR circuit (cathode of the diode D5). When the divided voltage is smaller than the voltage of the PFC signal, the OR circuit (cathode of the diode D6) Outputs the voltage of the PFC signal. The divided voltage or the voltage of the PFC signal output from the OR circuit is divided by the second voltage dividing circuit and input to the inverting input terminal of the operational amplifier OP1. The voltage obtained by dividing the divided voltage by the second voltage dividing circuit corresponds to the “second voltage” of the present invention, and the voltage obtained by dividing the voltage of the PFC signal by the second voltage dividing circuit is the “third voltage” of the present invention. ".

  The first voltage generated by the resistor R5 is input to the non-inverting input terminal of the operational amplifier OP1. The operational amplifier OP1 compares the second or third voltage input to the inverting input terminal with the first voltage input to the non-inverting input terminal, and when the first voltage is higher than the second or third voltage. A high-level signal (the “overcurrent signal” of the present invention) is output, and a low-level signal is output when the first voltage is lower than the second or third voltage. The high-level signal, that is, the overcurrent signal, output from the output terminal of the operational amplifier OP1 is input to the first control circuit 6 via the photocoupler PC3.

  The first control circuit 6 includes a first terminal that outputs a PWM control signal of the switch Q1, a second terminal that outputs a PWM control signal of the switch Q2, and a third terminal to which a power supply voltage is input from the auxiliary power supply circuit 4. , A fourth terminal to which a PFC signal is input via a second signal transmission means (a photocoupler in the present embodiment) PC2, fifth and sixth terminals connected to GND, and an overcurrent signal. It has a seventh terminal and an eighth terminal to which a feedback signal is input via a first signal transmission means (photocoupler in the present embodiment) PC1.

  The first control circuit 6 executes the switching operation of the switch Q1 when the PFC signal is input to the fourth terminal, and stops the switching operation of the switch Q1 when the PFC signal is not input to the fourth terminal. Let it. The first control circuit 6 stops the switching operation of the switch Q2 when the overcurrent signal is input to the seventh terminal, and stops the switching operation of the switch Q2 when the overcurrent signal is not input to the seventh terminal. Is executed. Further, the first control circuit 6 controls the PWM duty of the switch Q2 according to the feedback signal input to the eighth terminal, so that the output voltage (second DC voltage) supplied to the load becomes a constant value. Hold.

  The second control circuit 7 is an output voltage detection circuit for detecting the second DC voltage, and as described above, maintains the output voltage (second DC voltage) at a constant value. A signal (feedback signal) relating to the number is input to the eighth terminal of the first control circuit 6 via the photocoupler PC1.

  Next, an overcurrent protection operation of the switching power supply device 1 will be described with reference to FIG. The overcurrent protection operation refers to an operation in which, when an overcurrent signal is input to the seventh terminal of the first control circuit 6, the first control circuit 6 stops the switching operation of the switch Q2 and reduces the output current. Say.

  The overcurrent point at which the overcurrent protection operation is performed in the switching power supply device 1 is different between the light load mode (when the PFC signal is not input) and the heavy load mode (when the PFC signal is input). As shown in FIG. 2, in the light load mode, the overcurrent protection operation is performed when the output current supplied to the load (flowing through the resistor R5) reaches the overcurrent point P1, whereas the heavy current protection operation is performed. In the load mode, the overcurrent protection operation is not performed until the output current exceeds the overcurrent point P1 and reaches the overcurrent point P2.

  As shown in FIG. 3A, in the light load mode, the first voltage (OP1 + voltage) generated by the resistor R5 is input to the non-inverting input terminal of the operational amplifier OP1, and is input to the inverting input terminal of the operational amplifier OP1. Is supplied with a second voltage (OP1-voltage) proportional to the output voltage (second DC voltage). Since the output voltage is kept constant under the control of the first control circuit 6, the second voltage is also kept constant. On the other hand, the first voltage increases in proportion to the output current. The operational amplifier OP1 compares the second voltage with the first voltage, and outputs an overcurrent signal when the first voltage becomes larger than the second voltage. That is, the point where the first voltage and the second voltage match is the overcurrent point P1. FIGS. 3A and 3B show only the relationship between the voltage of the operational amplifier OP1 and the output current, and do not consider the overcurrent protection operation.

  As shown in FIG. 3B, in the heavy load mode, the first voltage (OP1 + voltage) generated by the resistor R5 is input to the non-inverting input terminal of the operational amplifier OP1, and is input to the inverting input terminal of the operational amplifier OP1. Is larger than the second voltage or the third voltage proportional to the voltage of the PFC signal (OP1-voltage). With reference to the potential of GND of the operational amplifier OP1, the potential of GND of the PFC signal is reduced by the voltage generated by the resistor R5, so that the third voltage decreases in proportion to the output current. In the switching power supply device 1, usually, the voltage of the PFC signal is set so that the third voltage is higher than the second voltage. Therefore, the operational amplifier OP1 compares the third voltage with the first voltage, and outputs an overcurrent signal when the first voltage becomes larger than the third voltage. That is, the point where the first voltage matches the third voltage is the overcurrent point P2, and the overcurrent point P2 has a value larger than the overcurrent point P1.

  After all, in the switching power supply 1, unlike the conventional switching power supply 11 shown in FIG. 4, a switch that switches on / off in accordance with the load mode, that is, input / non-input of the PFC signal (the switch Q3 of the switching power supply 11) Is unnecessary, so that the overcurrent point can be changed to an appropriate value according to the load mode without increasing the component cost.

  The embodiments of the switching power supply device according to the present invention have been described above, but the present invention is not limited to the above embodiments.

  For example, the overcurrent signal output circuit of the present invention is configured such that (1) a second DC voltage and a voltage of a PFC signal are input, and a second voltage proportional to the second DC voltage or a third voltage proportional to the voltage of the PFC signal. A selection circuit that outputs the larger one of them, (2) a voltage generation circuit that generates a first voltage proportional to the output current supplied to the load, and (3) a second voltage or a second voltage that is input from the selection circuit. If the third voltage is compared with the first voltage and a comparison circuit that outputs an overcurrent signal when the first voltage is higher than the second voltage or the third voltage is included, the configuration is appropriately changed. be able to.

  The configuration of the PFC circuit of the present invention can be appropriately changed as long as the PFC circuit includes the first switch and converts the input voltage to the first DC voltage while improving the power factor by the switching operation of the first switch.

  The DC / DC converter circuit of the present invention includes a second switch, and the configuration can be appropriately changed as long as the first DC voltage is converted to the second DC voltage by the switching operation of the second switch.

  The control circuit (first control circuit) of the present invention receives the PFC signal and the overcurrent signal, and executes / stops the switching operation of the first switch according to the input / non-input of the PFC signal. If the switching operation of the second switch is stopped / executed in response to input / non-input, the configuration can be appropriately changed.

  At least one of the auxiliary power supply circuit 4 and the second control circuit 7 in the above embodiment can be excluded from the configuration of the present invention.

  The present invention also includes a switching power supply device further provided with a load mode other than the light load mode and the heavy load mode.

Reference Signs List 1 switching power supply device 2 PFC circuit 3 DC / DC converter circuit 4 auxiliary power supply circuit 5 overcurrent signal output circuit 6 first control circuit 7 second control circuit

Claims (2)

A PFC circuit that includes a first switch and converts an input voltage to a first DC voltage while improving a power factor by a switching operation of the first switch;
A DC / DC converter circuit that includes a second switch and converts the first DC voltage into a second DC voltage by a switching operation of the second switch;
A switching power supply for supplying the second DC voltage to a load,
A PFC signal and an overcurrent signal are input, and the switching operation of the first switch is executed / stopped according to the input / non-input of the PFC signal, while the second operation is performed according to the input / non-input of the overcurrent signal. A control circuit for stopping / executing the switching operation of the switch;
An overcurrent signal output circuit that outputs the overcurrent signal to the control circuit;
With
The overcurrent signal output circuit,
A selection circuit to which the second DC voltage and the voltage of the PFC signal are input and that outputs a larger one of a second voltage proportional to the second DC voltage or a third voltage proportional to the voltage of the PFC signal When,
A voltage generation circuit that generates a first voltage proportional to an output current supplied to the load;
Comparing the second voltage or the third voltage input from the selection circuit with the first voltage, and when the first voltage is higher than the second voltage or the third voltage, the overcurrent signal; And a comparison circuit that outputs a signal. The voltage generation circuit includes a resistor that detects the output current,
The selection circuit includes an OR circuit including a first diode and a second diode for outputting a larger one of the second voltage and the third voltage,
The comparison circuit has a first input terminal to which the second voltage or the third voltage is input, a second input terminal to which the first voltage is input, and an output terminal that outputs the overcurrent signal. The switching power supply according to claim 1, further comprising an operational amplifier.

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