JP2015077002A - Switching power source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power source device that is able to improve efficiency in switching operation.SOLUTION: A switching power source device comprises: a voltage detecting section 2 that feeds back the voltage value of a secondary side DC voltage Vcc3 to a control section IC1; a switching operation command section 3 that outputs an on/off command on the basis of the magnitude relation between the voltage value of the secondary-side DC voltage Vcc3 and the minimum/maximum swing voltage value and, at the same time, outputs an on-command in a case where the load is in a normal operating state; a control section IC1 that controls the duty ratio of switching means Q1 and, also, performs/stops a switching operation according to the on/off command; and a blocking section 4 that blocks supply of voltage to the voltage detecting section 2 when load is in a standby state. When the supply of voltage to the voltage detecting section 2 is blocked by the blocking section 4, the voltage value fed back from the voltage detecting section 2 is made irrelevant to the actual voltage value of the secondary side DC voltage Vcc3.

Description

  The present invention relates to a switching power supply device.

  2. Description of the Related Art Conventionally, there is known a two-output switching power supply device that outputs a main output voltage and a sub output voltage obtained by stepping down the main output voltage (see, for example, Patent Document 1). A two-output switching power supply apparatus 1C as shown in FIG. 6 is also known in which the execution and stop of the switching operation are alternately repeated (swing operation is performed) in the state.

  This two-output type switching power supply device 1C includes a switching means Q1 composed of an n-channel MOS transistor connected to the primary side of the transformer T1, a control unit IC1 for controlling the switching means Q1, and a secondary side DC serving as a main output voltage. The voltage detection unit 2 detects the voltage value of the voltage Vcc3 and feeds it back to the control unit IC1, the switching operation command unit 3 that outputs an on / off command to the control unit IC1, and the secondary side of the transformer T1. Switching element Q4 that is turned off when the loaded load is in a standby state, a load state notification circuit IC4 that changes the state of the OUT terminal according to the state of the load, and a DC / DC converter that steps down the secondary side DC voltage Vcc3 Circuit IC5. When the load is in a normal operation state, the 2-output switching power supply device 1C outputs a main output voltage (for example, 24.0V) and a sub output voltage (for example, 5.0V), and the load is in a standby state. Only the output voltage (for example, 5.0V) is output.

  The control unit IC1 has an ON / OFF terminal. When the potential of the ON / OFF terminal becomes low level, the control unit IC1 executes the switching operation of the switching means Q1, while when the potential of the ON / OFF terminal becomes high level, The switching operation of the switching means Q1 is stopped.

  The switching operation command unit 3 outputs an ON command to the control unit IC1 when the load is in a normal operation state. Specifically, the swing circuit IC3 outputs a low level signal according to the state of the OUT terminal of the load state notification circuit IC4, the photocoupler PC2 is turned off, and the switching element Q2 made of an n-channel MOS transistor is turned on. It becomes. Thereby, the potential of the ON / OFF terminal of the control unit IC1 becomes a low level, and the control unit IC1 executes the switching operation of the switching means Q1.

  On the other hand, when the load is in a standby state, the switching operation command unit 3 alternately outputs an on command and an off command to the control unit IC1. When the control unit IC1 executes the switching operation based on the ON command, the voltage value of the secondary side DC voltage Vcc3 increases, while when the control unit IC1 stops the switching operation based on the OFF command, the voltage detection unit 2 The voltage value of the secondary side DC voltage Vcc3 gradually decreases due to power loss generated in the switching operation command unit 3, the DC / DC converter circuit IC5, the load, and the like. As a result, in the two-output switching power supply device 1C, as shown in FIG. 7, the voltage value of the secondary side DC voltage Vcc3 is preset to a preset maximum swing voltage value Vcc3_max (for example, 22.4V). Swing between the minimum swing voltage value Vcc3_min (for example, 8.0V). In this way, the operation of swinging the secondary DC voltage Vcc3 by alternately executing and stopping the switching operation is referred to as “swing operation”.

FIG. 8 is a diagram showing the voltage value of the secondary side DC voltage Vcc3 and the state of the switching means Q1 during the period Ta in FIG. As shown in the figure, the voltage value of the secondary side DC voltage Vcc3 until below the minimum swing voltage value Vcc3_min (time t ₁ earlier), the switching operation command unit 3 outputs an OFF instruction, the control unit IC1 switching The switching operation of the means Q1 is stopped. Until the voltage value of the secondary side DC voltage Vcc3 falls below the minimum swing voltage value Vcc3_min and exceeds the maximum swing voltage value Vcc3_max (time t ₁ to time t ₂ ), the switching operation command unit 3 outputs an on command, The controller IC1 causes the switching means Q1 to perform the switching operation. When the voltage value of the secondary side DC voltage Vcc3 exceeds the maximum swing voltage value Vcc3_max (time _{t 2} later), the switching operation command unit 3 outputs an OFF instruction, the control unit IC1 is the switching operation of the switching means Q1 Stop.

JP 2002-17084 A

  By the way, in the conventional two-output switching power supply device 1C, while the ON command is output from the switching operation command unit 3, the control unit IC1 determines the voltage of the secondary side DC voltage Vcc3 fed back from the voltage detection unit 2. The duty ratio of the switching means Q1 is controlled so that the value falls within a preset target voltage range.

  Specifically, when the fed back voltage value is smaller than the lower limit value Vo1_min (for example, 23.4 V) of the target voltage range shown in FIG. 7, the control unit IC1 increases the voltage value of the secondary side DC voltage Vcc3. The duty ratio of the switching means Q1 is increased so that On the other hand, when the fed back voltage value is larger than the upper limit value Vo1_max (for example, 24.6V) of the target voltage range, the control unit IC1 sets the switching means Q1 so that the voltage value of the secondary side DC voltage Vcc3 becomes small. Reduce the duty ratio.

  Further, when the fed back voltage value is within the target voltage range, that is, when the fed back voltage value substantially matches a predetermined target voltage value (for example, 24.0 V), the control unit IC1 The duty ratio of the switching means Q1 is hardly changed so that the voltage value of the secondary side DC voltage Vcc3 is maintained. Therefore, when the maximum swing voltage value Vcc3_max is set to a value close to the target voltage value, the rate of change of the voltage value (duty ratio of the duty ratio) increases as the voltage value of the secondary side DC voltage Vcc3 approaches the maximum swing voltage value Vcc3_max. (Change rate) becomes small, and it may take an excessive time for the voltage value to reach the maximum swing voltage value Vcc3_max, or the swing operation may not be performed without the voltage value reaching the maximum swing voltage value Vcc3_max. is there. Therefore, in the two-output switching power supply device 1C, the maximum swing voltage value Vcc3_max is set to a value smaller than the lower limit value Vo1_min of the target voltage range so that the swing operation is reliably performed (see FIG. 7).

  As a result, in the two-output switching power supply apparatus 1C, the difference between the maximum swing voltage value Vcc3_max and the minimum swing voltage value Vcc3_min becomes small, and a period for stopping the switching operation of the switching means Q1 (period Tb2 in FIG. 7) is sufficient. The switching loss during the swing operation cannot be sufficiently reduced.

  This invention is made | formed in view of the said situation, The place made into the subject is providing the switching power supply device which can improve the efficiency at the time of swing operation | movement.

  In order to solve the above-described problems, a switching power supply according to the present invention includes (1) a transformer and a switching unit connected to the primary side of the transformer, and generates an AC voltage from the primary side DC voltage by a switching operation of the switching unit. Then, the AC voltage is converted to DC to generate a secondary side DC voltage. When the load provided on the secondary side of the transformer is in a normal operation state, the secondary side DC voltage is supplied to the load, and the load is on standby. A switching power supply device for stopping the supply of the secondary side DC voltage to the load when in a state, a voltage detection unit for detecting the voltage value of the secondary side DC voltage and feeding back to the primary side of the transformer; When the load is in a standby state, an ON command is output based on the magnitude relationship between the voltage value of the secondary side DC voltage and the preset minimum swing voltage value, while the secondary side A switching operation command unit that outputs an off command based on the magnitude relationship between the voltage value of the current voltage and a preset maximum swing voltage value, and outputs an on command when the load is in a normal operation state; When a command is input, the switching operation is executed, and the duty ratio or switching frequency of the switching means is controlled so that the voltage value fed back from the voltage detection unit falls within a preset target voltage range, while off A control unit that stops the switching operation when a command is input, and a blocking unit that blocks voltage supply to the voltage detection unit when the load is in a standby state. When the voltage supply is cut off, the voltage value fed back from the voltage detector becomes irrelevant to the actual voltage value of the secondary side DC voltage. And wherein the door.

  According to this configuration, power loss in the voltage detection unit can be eliminated by cutting off the voltage supply to the voltage detection unit when the load is in a standby state. As a result, the voltage value of the secondary side DC voltage decreases more slowly when the switching operation is stopped, and the period during which the switching operation is stopped becomes longer, so that the switching loss during the swing operation can be reduced.

  Further, according to this configuration, when the load is in the standby state, the voltage value fed back from the voltage detection unit becomes independent of the actual voltage value of the secondary side DC voltage. As the voltage value approaches the target voltage range, the rate of change of the voltage value (duty ratio change rate) does not decrease, and the maximum swing voltage value must be set to a value smaller than the lower limit value of the target voltage range. The restriction of not being able to be eliminated can be eliminated.

  In the switching power supply device of (1), it is preferable that (2) the maximum swing voltage value is larger than the lower limit value of the target voltage range, and the minimum swing voltage value is smaller than the lower limit value of the target voltage range.

  According to this configuration, the difference between the maximum swing voltage value and the minimum swing voltage value increases, and the period during which the switching operation is stopped becomes longer, so that the switching loss during the swing operation can be further reduced.

  In the switching power supply device of the above (1) or (2), (3) the switching operation command unit determines that the voltage value of the secondary side DC voltage has fallen below the minimum swing voltage value when the load is in a standby state. An on command is output as a trigger, and the on command continues to be output until the voltage value exceeds the maximum swing voltage value, while an off command is issued when the voltage value of the secondary side DC voltage exceeds the maximum swing voltage value. It can be configured to output and continue to output the off command until the voltage value falls below the minimum swing voltage value.

  In the switching power supply device of (1) to (3), (4) the voltage detection unit is connected in parallel to the series circuit including the light emitting diode of the photocoupler and the shunt regulator, and the voltage dividing point. Has a voltage dividing resistor circuit connected to the reference terminal of the shunt regulator and a photocoupler phototransistor connected to the control unit, one end of the series circuit being connected to the blocking unit, and the other end being a transformer It can be configured to be connected to the low potential line on the next side.

  In the switching power supply device of (4) above, (5) the interrupting unit is composed of a switching element that is turned off when the load is in a standby state, and the switching element has a high potential on one end of the current path on the transformer secondary side. The other end of the current path may be connected to one end of the series circuit.

  Further, in the switching power supply device of (4), (6) the shut-off unit includes a switching element that shuts off the supply of the secondary side DC voltage to the load when the load is in a standby state, and detects the voltage. The part may be provided on the load side with respect to the switching element.

  ADVANTAGE OF THE INVENTION According to this invention, the switching power supply device which can improve the efficiency at the time of swing operation | movement can be provided.

1 is a circuit diagram of a switching power supply device according to a first embodiment of the present invention. It is a circuit diagram of the load state notification circuit in the present invention. It is a circuit diagram of a swing circuit in the present invention. It is a figure which shows the swing operation | movement in the switching power supply device which concerns on 1st Embodiment of this invention. It is a circuit diagram of the switching power supply device concerning a 2nd embodiment of the present invention. It is a circuit diagram of the conventional switching power supply device. It is a figure which shows the swing operation | movement in the conventional switching power supply apparatus. It is a figure which shows the state of the switching means in period Ta of FIG.

  Referring to the attached drawings, a preferred embodiment of a switching power supply according to the present invention will be described below. A two-output switching power supply (two-output isolated DC / DC) having a DC / DC converter circuit connected to the output side of a flyback converter. A DC converter will be described as an example.

[First Embodiment]
FIG. 1 shows a switching power supply apparatus 1A according to the first embodiment of the present invention. As shown in the figure, the switching power supply device 1A includes a transformer T1 having a primary side main winding N1, a secondary side main winding N2, and an auxiliary winding N3, and is provided on the secondary side of the transformer T1. When a load (not shown) is in a normal operation state, a main output voltage (for example, 24.0V) and a sub output voltage (for example, 5.0V) are supplied to the load, and the load is in a standby state (light load state). In this case, only an output voltage (for example, 5.0 V) is supplied according to the load.

  The switching power supply 1A includes an n-channel connected to the primary main winding N1 of the transformer T1 in addition to the transformer T1 (for the transformer T1, the side marked with ● is one end and the other side is the other end). A switching means Q1 comprising a MOS transistor, a control part IC1 for controlling the switching means Q1, a voltage detection part 2 for detecting the voltage value of the secondary side DC voltage Vcc3 as the main output voltage and feeding back to the control part IC1, A switching operation command unit 3 for outputting an on / off command to the control unit IC1, a blocking unit 4 having a switching element Q3 made of a p-channel MOS transistor, a switching element Q4 made of a p-channel MOS transistor, and a load state notification A DC / DC converter that steps down the circuit IC4 and the secondary side DC voltage Vcc3 to generate a subordinate output voltage. A converter circuit IC 5, and a.

  The control unit IC1 is a switching power supply control IC having a Vcc terminal, a GND terminal, an FB terminal, and an ON / OFF terminal. The Vcc terminal is connected to one end of the primary main winding N1 via the starting resistor R1, and is connected to one end of the auxiliary winding N3 via a rectifying / smoothing circuit including the rectifying diode D1 and the smoothing capacitor C2. . The FB terminal is connected to the collector of the first phototransistor of the first photocoupler PC1 constituting the voltage detection unit 2. The ON / OFF terminal is connected to one end (drain) of a current path of a switching element (in this embodiment, an n-channel MOS transistor) Q2 constituting the switching operation command unit 3.

  The controller IC1 executes the switching operation of the switching means Q1 when the potential of the ON / OFF terminal becomes low level, and stops the switching operation of the switching means Q1 when the potential of the ON / OFF terminal becomes high level. Further, when the control unit IC1 executes the switching operation of the switching unit Q1, the duty ratio (ON width) of the switching unit Q1 is set so that the voltage value fed back from the voltage detection unit 2 falls within a preset target voltage range. ) Or control the switching frequency. In the present embodiment, the control unit IC1 controls the duty ratio of the switching means Q1.

  The voltage detection unit 2 has one end connected to the other end (drain) of the current path of the switching element Q3 constituting the cutoff unit 4 and the other end connected to one end of the secondary main winding N2. Circuits R4 and R5, a first light emitting diode of the first photocoupler PC1 whose anode is connected to one end of the voltage dividing resistor circuit R4 and R5, and an anode which is connected to the other end of the voltage dividing resistor circuit R4 and R5, and a cathode Is connected to the cathode of the first light emitting diode, the reference terminal is connected to the voltage dividing point of the voltage dividing resistor circuit R4, R5, the collector is connected to the FB terminal of the control unit IC1, and the emitter is And a first phototransistor of the first photocoupler PC1 connected to the GND terminal of the control unit IC1.

  When the switching element Q3 is in the on state (the load is in a normal operation state), the voltage detection unit 2 converts the AC voltage induced in the secondary side main winding N2 into a direct current with a rectifying and smoothing circuit including the rectifying diode D2 and the smoothing capacitor C3. The converted secondary side DC voltage Vcc3 is detected and fed back to the control unit IC1.

  More specifically, when the voltage value of the secondary side DC voltage Vcc3 is larger than a preset target voltage value (for example, 24.0 V), the voltage detection unit 2 determines the voltage value of the secondary side DC voltage Vcc3 and the target value. The current flowing through the first light emitting diode of the first photocoupler PC1 is increased according to the difference from the voltage value, and the collector current that is absorbed by the first phototransistor of the first photocoupler PC1 is increased. As a result, since the potential of the FB terminal of the control unit IC1 is lowered, the control unit IC1 reduces the duty ratio of the switching means Q1 according to the lowered amount.

  On the other hand, when the voltage value of the secondary side DC voltage Vcc3 is smaller than the target voltage value, the voltage detector 2 changes the first light emitting diode according to the difference between the voltage value of the secondary side DC voltage Vcc3 and the target voltage value. The flowing current is reduced, and the collector current of the first phototransistor is reduced. As a result, since the potential of the FB terminal of the control unit IC1 increases, the control unit IC1 increases the duty ratio of the switching means Q1 according to the increased amount.

  Further, when the voltage value of the secondary side DC voltage Vcc3 substantially matches the target voltage value, that is, the voltage value is the upper limit value Vo1_max (for example, 24.6 V) of the target voltage range and the lower limit value of the target voltage range. When it is between Vo1_min (for example, 23.4 V), the current flowing through the first light emitting diode hardly changes, and the collector current of the first phototransistor hardly changes. As a result, since the potential of the FB terminal of the control unit IC1 hardly changes, the control unit IC1 hardly changes the duty ratio of the switching means Q1.

  In addition, when the switching element Q3 is in the off state (the load is in the standby state), the voltage detection unit 2 cannot detect the voltage value of the secondary side DC voltage Vcc3, so that the voltage value fed back to the control unit IC1 is two. It becomes unrelated to the actual voltage value of the secondary side DC voltage Vcc3.

  More specifically, since no current flows through the first light-emitting diode of the first photocoupler PC1 in the voltage detection unit 2, the collector current absorbed by the first phototransistor of the first photocoupler PC1 becomes zero. As a result, since the potential of the FB terminal of the control unit IC1 is significantly increased, the control unit IC1 recognizes that the voltage value of the secondary side DC voltage Vcc3 is much smaller than the target voltage value, and the duty of the switching means Q1. Maximize the ratio. For this reason, in the switching power supply device 1A, unlike the conventional switching power supply device 1C, the limitation that the maximum swing voltage value Vcc3_max described later must be set to a value smaller than the lower limit value Vo1_min of the target voltage range may be eliminated. it can.

  The switching element Q3 constituting the blocking unit 4 has a source connected to the cathode of the rectifying diode D2 constituting the rectifying and smoothing circuit, a drain connected to the anode of the first light emitting diode of the first photocoupler PC1, and a gate switching. The gate of the element Q4 and the voltage dividing points of the voltage dividing resistor circuits R7 and R8 are connected. The switching element Q3 is turned on when the load is in a normal operation state, and is turned off when the load is in a standby state.

  The switching element Q4 has a source connected to the cathode of the rectifier diode D2 and the source of the switching element Q3, and a drain connected to a high potential side output terminal that outputs the main output voltage. Similarly to the switching element Q3, the switching element Q4 is turned on when the load is in a normal operation state, and is turned off when the load is in a standby state.

  The load state notification circuit IC4 includes an IN terminal to which an external signal corresponding to the load state is input, a GND2 terminal connected to a low potential side output terminal that outputs a sub output voltage, and a switching operation command unit 3. And an OUT terminal connected to the control terminals (gates) of the switching elements Q3 and Q4 via the resistor R7. More specifically, as shown in FIG. 2, the load state notification circuit IC4 includes a switching element Q5 composed of an n-channel MOS transistor. The control terminal (gate) of the switching element Q5 corresponds to the IN terminal, one end (drain) of the current path of the switching element Q5 corresponds to the OUT terminal, and the other end (source) of the current path of the switching element Q5 corresponds to the GND2 terminal. Equivalent to.

  In the load state notification circuit IC4, when the load is in a normal operation state, a high level external signal is input to the IN terminal. As a result, the switching element Q5 is turned on (conductive state), so that the potential of the OUT terminal becomes low level, and the current output from the rectifying / smoothing circuit including the rectifying diode D2 and the smoothing capacitor C3 is the voltage dividing resistor circuit R7 , Flows through R8. As a result, a voltage drop occurs in the resistor R8, the gate-source voltage of the switching elements Q3 and Q4 increases, and the switching elements Q3 and Q4 are turned on. On the other hand, when the load is in a standby state, a low-level external signal is input to the IN terminal. As a result, the switching element Q5 is turned off (non-conducting state), so that the potential at the OUT terminal becomes a high level, and the current output from the rectifying and smoothing circuit does not flow through the voltage dividing resistor circuits R7 and R8. As a result, the gate-source voltages of the switching elements Q3 and Q4 are lowered, and the switching elements Q3 and Q4 are turned off.

  Referring to FIG. 1 again, switching operation command unit 3 has swing circuit IC3, second photocoupler PC2, and switching element (n-channel MOS transistor) Q2, and when the load is in a normal operation state. While an ON command is output to the control unit IC1, an ON command and an OFF command are alternately output to the control unit IC1 when the load is in a standby state.

  The switching element Q2 has a drain connected to the ON / OFF terminal of the control unit IC1, a source connected to the low potential side input terminal, and a gate connected to the Vcc terminal of the control unit IC1 via the resistor R2. . A resistor R3 is interposed between the gate and source of the switching element Q2.

  The second phototransistor of the second photocoupler PC2 has a collector connected to the gate of the switching element Q2, and an emitter connected to the source of the switching element Q2. The second light-emitting diode of the second photocoupler PC2 has an anode connected to the OUT terminal of the swing circuit IC3 via the resistor R6, and a cathode connected to the GND1 terminal of the swing circuit IC3.

  The swing circuit IC3 has a Vcc3 terminal connected to a connection point between the source of the switching element Q3 and the source of the switching element Q4, an ON / OFF terminal connected to the OUT terminal of the load state notification circuit IC4, and a main output voltage. It has a GND1 terminal connected to the output terminal on the low potential side for output, and an OUT terminal connected to the second light emitting diode of the second photocoupler PC2 via the resistor R6.

  More specifically, as shown in FIG. 3, the swing circuit IC3 includes a series circuit composed of a resistor R12 and a Zener diode ZD1 having one end connected to the Vcc3 terminal and the other end connected to the GND1 terminal, and is connected in parallel to the series circuit. And the inverting input terminal (− terminal) is connected to the connection point of the resistor R12 and the Zener diode ZD1, and the non-inverting input terminal (+ terminal) is the voltage dividing resistor circuit R10, R11. And an operational amplifier Amp1 whose output terminal is connected to the non-inverting input terminal (+ terminal) via the OUT terminal and the resistor R9. The operational amplifier Amp1 is also connected to the ON / OFF terminal.

  When a low level signal is input from the ON / OFF terminal to the operational amplifier Amp1, that is, when the potential of the OUT terminal of the load state notification circuit IC4 is low level (when the load is in a normal operation state), the output of the operational amplifier Amp1 is Fixed at low level. As a result, a low level signal is output from the OUT terminal of the swing circuit IC3, and the second photocoupler PC2 is turned off. When the second photocoupler PC2 is turned off, a voltage difference corresponding to the voltage drop generated by the resistor R3 is generated between the gate and the source of the switching element Q2, so that the switching element Q2 is turned on. As a result, the ON / OFF terminal of the control unit IC1 becomes low level, and the control unit IC1 executes the switching operation of the switching means Q1.

  On the other hand, when a high level signal is input from the ON / OFF terminal to the operational amplifier Amp1, that is, when the potential of the OUT terminal of the load state notification circuit IC4 is high level (when the load is in a standby state), the operational amplifier Amp1 is The hysteresis operation described later is performed.

  That is, the operational amplifier Amp1 is a low-level signal triggered by the voltage value of the Vcc3 terminal (voltage value of the secondary side DC voltage Vcc3) being lower than a preset minimum swing voltage value Vcc3_min (for example, 8.0 V). And a low level signal is continuously output until the voltage value at the Vcc3 terminal exceeds a preset maximum swing voltage value Vcc3_max (for example, 23.6 V), while the voltage value at the Vcc3 terminal is the maximum swing voltage value Vcc3_max. A high level signal is output as a result of exceeding the threshold value, and the high level signal is continuously output until the voltage value at the Vcc3 terminal falls below the minimum swing voltage value Vcc3_min.

  As a result, the second photocoupler PC2 is turned off and the switching element Q2 is turned on until the voltage value of the secondary side DC voltage Vcc3 falls below the minimum swing voltage value Vcc3_min and exceeds the maximum swing voltage value Vcc3_max. Therefore, the control unit IC1 causes the switching means Q1 to perform the switching operation. On the other hand, during the period from when the voltage value of the secondary side DC voltage Vcc3 exceeds the maximum swing voltage value Vcc3_max to below the minimum swing voltage value Vcc3_min, the second photocoupler PC2 is turned on, and the switching element Q2 is turned off. Therefore, the control unit IC1 stops the switching operation of the switching means Q1.

  When the control unit IC1 executes the switching operation of the switching means Q1, the voltage value of the secondary side DC voltage Vcc3 increases. When the control unit IC1 stops the switching operation of the switching means Q1, the switching operation command unit 3, DC The voltage value of the secondary side DC voltage Vcc3 gradually decreases due to power loss generated in the DC / DC converter circuit IC5 and the load. As a result, as shown in FIG. 4, the voltage value of the secondary side DC voltage Vcc3 swings between the maximum swing voltage value Vcc3_max and the minimum swing voltage value Vcc3_min.

  In the switching power supply device 1A, when the load is in the standby state, the switching element Q3 is turned off, and the voltage value fed back to the control unit IC1 becomes irrelevant to the actual voltage value of the secondary side DC voltage Vcc3. As the voltage value of the secondary DC voltage Vcc3 approaches the target voltage range, the voltage change rate (duty ratio change rate) does not decrease. Therefore, in the switching power supply device 1A, the maximum swing voltage value Vcc3_max can be set to a value larger than the lower limit value Vo1_min of the target voltage range. The maximum swing voltage value Vcc3_max is equal to or lower than the upper limit value Vo1_max of the target voltage range so that the main output voltage exceeding the upper limit value Vo1_max of the target voltage range is not supplied to the load when the load is switched from the standby state to the normal operation state. It is preferable to set the value.

  Further, in the switching power supply device 1A, when the load is in the standby state, the voltage supply to the voltage detection unit 2 is interrupted by the switching element Q3 being turned off, so that no power loss occurs in the voltage detection unit 2. . For this reason, in the switching power supply device 1A, the voltage value of the secondary side DC voltage Vcc3 when the switching operation of the switching means Q1 is stopped can be made lower than that in the conventional switching power supply device 1C.

  Eventually, in the switching power supply device 1A, the maximum swing voltage value Vcc3_max can be set to a value larger than the lower limit value Vo1_min of the target voltage range, and the secondary side DC voltage Vcc3 when the switching operation of the switching means Q1 is stopped. Since the voltage value can be gradually lowered, the period for stopping the switching operation (period Tb1 in FIG. 4) can be made longer than that of the conventional switching power supply apparatus 1C. Therefore, according to the switching power supply device 1A according to the present embodiment, the switching loss of the switching means Q1 during the swing operation can be reduced, and the efficiency during the swing operation can be improved.

[Second Embodiment]
FIG. 5 shows a switching power supply device 1B according to the second embodiment of the present invention. As shown in the figure, in the switching power supply device 1B, the switching element Q4 constitutes a cutoff part 4 ′, the voltage detection part 2 is connected to the load side with respect to the switching element Q4, and the switching element Except for not including Q3, most of them are common to the switching power supply device 1A according to the first embodiment.

  In the switching power supply device 1B, when the load is in a standby state, the voltage supply to the voltage detection unit 2 is interrupted by the switching element Q4 being turned off, so that no power loss occurs in the voltage detection unit 2. Therefore, in the switching power supply device 1B, the maximum swing voltage value Vcc3_max can be set to a value larger than the lower limit value Vo1_min of the target voltage range, similarly to the switching power supply device 1A according to the first embodiment. Since the decrease in the voltage value of the secondary side DC voltage Vcc3 when the switching operation of the means Q1 is stopped can be moderated, the period during which the switching operation is stopped can be lengthened. Therefore, according to the switching power supply device 1B according to the present embodiment, the switching loss of the switching means Q1 during the swing operation can be reduced, and the efficiency during the swing operation can be improved.

  As mentioned above, although preferable embodiment of the switching power supply device which concerns on this invention was described, this invention is not limited to the structure of said each embodiment.

  For example, in the first embodiment, the blocking unit 4 is configured by a switching element Q3 made of a p-channel MOS transistor, and in the second embodiment, the blocking unit 4 ′ is configured by a switching element Q4 made of a p-channel MOS transistor. However, the configuration of the blocking units 4 and 4 ′ can be changed as appropriate as long as the voltage supply to the voltage detection unit 2 can be blocked when the load is in a standby state.

  The voltage detector 2 can appropriately change the configuration as long as it can detect the voltage value of the secondary side DC voltage Vcc3 and feed back the voltage value to the controller IC1.

  The switching operation command unit 3 outputs an ON command based on the magnitude relationship between the voltage value of the secondary side DC voltage Vcc3 and the minimum swing voltage value Vcc3_min when the load is in a standby state, while the secondary side DC voltage If the off command is output based on the magnitude relationship between the voltage value of Vcc3 and the maximum swing voltage value Vcc3_max and the on command is output when the load is in a normal operation state, the configuration can be changed as appropriate. it can.

  When the ON command is output from the switching operation command unit 3, the control unit IC1 executes the switching operation of the switching unit Q1, and the switching unit so that the voltage value fed back from the voltage detection unit 2 is within the target voltage range. While controlling the duty ratio of Q1 or the switching frequency, if the switching operation of the switching means Q1 can be stopped when an OFF command is output from the switching operation command unit 3, the configuration can be changed as appropriate. it can. For example, the switching operation of the switching means Q1 is executed / stopped according to the amount of current flowing through the ON / OFF terminal, or the duty ratio of the switching means Q1 is controlled according to the amount of current flowing through the FB terminal. Can do.

  As the switching means Q1, transistors other than n-channel MOS transistors and other switching elements can be used.

  The load state notification circuit IC4 determines whether the load is in a normal operation state or a standby state based on the voltage value of the slave output voltage and the current value of the load current supplied to the load, and does not require an external signal. Configuration can be taken.

  In each of the above embodiments, the flyback converter is described as an example of the main output circuit that outputs the main output voltage, but an arbitrary converter such as a forward converter or an LLC resonant converter is used instead of the flyback converter. Can do.

  Furthermore, the present invention can be applied as appropriate to switching power supply devices other than the two-output insulated DC / DC converter.

1A, 1B Switching power supply device 2 Voltage detection unit 3 Switching operation command unit 4, 4 'Blocking unit

Claims (6)

A switching means connected to a transformer and a primary side of the transformer; an alternating voltage is generated from a primary side DC voltage by a switching operation of the switching means; and the alternating voltage is converted into a direct current to generate a secondary side DC voltage; The secondary side DC voltage is supplied to the load when the load provided on the secondary side of the transformer is in a normal operation state, and the secondary side DC voltage is supplied to the load when the load is in a standby state. A switching power supply device that stops being supplied to
A voltage detection unit that detects a voltage value of the secondary side DC voltage and feeds back to the primary side of the transformer;
When the load is in a standby state, an on command is output based on the magnitude relationship between the voltage value of the secondary side DC voltage and a preset minimum swing voltage value, while the voltage of the secondary side DC voltage A switching operation command unit that outputs an off command based on a magnitude relationship between a value and a preset maximum swing voltage value, and outputs the on command when the load is in a normal operation state;
When the ON command is input, the switching operation is executed, and the duty ratio or switching frequency of the switching means is set so that the voltage value fed back from the voltage detection unit falls within a preset target voltage range. On the other hand, when the off command is input, a control unit that stops the switching operation;
A blocking unit that blocks voltage supply to the voltage detection unit when the load is in a standby state;
Have
When the voltage supply to the voltage detection unit is interrupted by the blocking unit, the voltage value fed back from the voltage detection unit becomes independent of the actual voltage value of the secondary side DC voltage. Switching power supply.   2. The switching power supply device according to claim 1, wherein the maximum swing voltage value is larger than a lower limit value of the target voltage range, and the minimum swing voltage value is smaller than a lower limit value of the target voltage range.   The switching operation command unit outputs the ON command when the voltage value of the secondary side DC voltage falls below the minimum swing voltage value when the load is in a standby state, and the voltage value is While continuing to output the ON command until the maximum swing voltage value is exceeded, the OFF command is output when the voltage value of the secondary DC voltage exceeds the maximum swing voltage value, and the voltage value is 3. The switching power supply device according to claim 1, wherein the off command is continuously output until the value falls below the minimum swing voltage value. The voltage detector is
A series circuit consisting of a photocoupler light emitting diode and a shunt regulator;
A voltage dividing resistor circuit connected in parallel to the series circuit and having a voltage dividing point connected to a reference terminal of the shunt regulator;
A phototransistor of the photocoupler connected to the control unit;
Have
4. The switching power supply device according to claim 1, wherein one end of the series circuit is connected to the blocking portion, and the other end is connected to a low potential line on the secondary side of the transformer. The blocking unit is composed of a switching element that is turned off when the load is in a standby state,
5. The switching element according to claim 4, wherein one end of a current path is connected to a high potential line on the transformer secondary side, and the other end of the current path is connected to one end of the series circuit. The switching power supply device described. The blocking unit includes a switching element that blocks the supply of the secondary DC voltage to the load when the load is in a standby state.
The switching power supply device according to claim 4, wherein the voltage detection unit is provided on the load side with respect to the switching element.

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