JP5915471B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply, and more particularly to a switching power supply including a main power supply unit and a standby power supply.

  A switching power supply such as an audio device is usually disposed on the primary side of insulation including a control circuit. For example, Patent Document 1 below includes a main power supply unit and a standby power supply unit, and both the switching control unit of the main power supply unit and the switching control unit of the standby power supply are provided on the primary side of the transformer.

  In Patent Documents 2 and 3, failure detection that establishes a conduction state in the auxiliary conduction path for a certain period after the power is turned on, detects an overload condition, and turns off a part of the conduction path. It is described that when the device establishes a conducting state in a part of the conducting path, the auxiliary conducting path becomes non-conducting and maintains the non-conducting state of the auxiliary conducting path until the power is turned off.

  In Patent Document 4, a first photocoupler is inserted into a circuit that feeds back a DC output voltage to an error amplifier circuit of a control circuit, and a second photocoupler is fed back to a circuit that feeds back a DC output current to an overcurrent detection circuit of the control circuit. It is described that couplers are inserted and these photocouplers are driven by an auxiliary power source which is a power source of a control circuit.

JP 2010-4596 A Special table 2001-503958 gazette Japanese Patent No. 3778438 JP-A-62-2857

  The primary side of the switching power supply is higher in voltage than the secondary side, and safety requirements are higher.Therefore, parts that comply with safety standards or protective elements are installed to prevent fires due to damage to these elements. It is necessary to provide a large number, resulting in an increase in cost and the number of parts. In addition, switching power supplies are required to reduce power consumption during standby.

  Thus, in a switching power supply including a main power supply and a standby power supply, a circuit configuration in which the main power supply is driven on the secondary side of the standby power supply can be considered, but noise due to the standby power supply can be a problem. That is, as a standby power supply, it is conceivable to use a PWM (Pulse Width Modulation) power supply and a PFM (Pulse Frequency Modulation) power supply, or a mixture of these as a low output and inexpensive power supply. In addition, the beat generated by the operating frequency of the standby power supply and the noise of the standby power supply itself become a problem, which may have an adverse effect when applied to an audio apparatus.

  An object of the present invention is to reduce power consumption during standby in a switching power supply and to reliably prevent noise caused by the standby power supply.

The switching power supply of the present invention is provided on the primary side of the main transformer, the switch element that switches the power supplied to the main transformer, the secondary element of the main transformer, and the switch element A main power supply comprising a main power supply control circuit for on / off control; a standby transformer; a standby power supply control circuit provided on a primary side of the standby transformer for switching power supplied to the standby transformer; and a secondary of the standby transformer A standby power supply provided with a standby power supply control feedback circuit that controls an operation of the standby power supply control circuit according to an output voltage of the main power supply, and the main power supply control circuit and the standby transformer of the standby power supply. Connect on / off And a set control circuit that is provided on the secondary side of the standby transformer and that controls the on / off of the switch. In the standby state, the standby power supply control circuit is in an operating state and is set from the standby transformer to the set. The power is supplied to the control circuit, and the set control circuit controls the switch to be turned off to stop the operation of the main power supply control circuit and the main power supply. In the power-on state, the set control circuit turns on the switch. The standby power supply is supplied with power from the standby transformer to the main power supply control circuit, and the main power supply control circuit and the main power supply are operated to output power from the main transformer. The standby power supply control circuit according to the output from the main transformer Characterized by the halt condition.

  In the present invention, in the standby state, the main power supply is in an operation stop state (off state), and the standby power supply is in an operation state (on state). When switching from the standby state to the power-on state, the set control circuit that operates with power supplied from the standby power supply controls the switch on, and the main power supply control circuit of the main power supply operates with power supplied from the standby power supply. Then, the switch element is turned on / off to turn on the main power supply. In the on state of the main power supply, electric power is generated from the main transformer, and the power supply voltage is supplied to each subsequent load to operate the apparatus. Also, the output from the main power supply is fed back to the standby power supply by the standby power supply control feedback circuit. When the power supply voltage is output from the main power supply, the standby power control feedback circuit turns off the standby power supply control circuit and sets the standby power supply. Is turned off. Even when the standby power supply is turned off in the power-on state, the power supply voltage is output from the main power supply, so that the set control circuit can operate with the power supply voltage from the main power supply.

  In one embodiment of the present invention, the standby power supply control feedback circuit, in a power-on state, stops the standby power supply control circuit when the output voltage of the main power supply exceeds a threshold, and And a threshold adjustment circuit connected to a feedback circuit for setting the threshold to a predetermined value. In another embodiment of the present invention, when the power is turned on and the input voltage from the outside is reduced, the standby power control feedback circuit responds to the power output from the main transformer. The standby power supply control circuit is set in an operating state, and power supply from the standby transformer to the set control circuit and the main power supply control circuit is maintained.

  In the present invention, in the standby state, the main power supply is in the operation stop state (off state) and the standby power supply is in the operation state (on state). In the power supply on state, the main power supply is in the operation state (on state) and the standby power supply is turned off. Since the operation is automatically stopped (OFF state), it is possible to reduce power consumption and to reliably prevent noise caused by the standby power supply when the power is turned on.

It is a circuit block diagram of the switching power supply in embodiment. It is a circuit block diagram of the switching power supply in other embodiment. It is a circuit block diagram of a threshold adjustment circuit. It is a circuit block diagram in the case of using a prior art.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, in the following embodiment, it is an illustration and this invention is not limited to the following embodiment.

<First Embodiment>
FIG. 1 shows a switching power supply for an audio apparatus according to this embodiment. The switching power supply includes a main power supply 10a and a standby power supply 10b.

  The main power supply 10a is a circuit that generates a power supply voltage and supplies it to the subsequent load 20 in a power-on state.

The standby power supply 10b is a circuit that generates a power supply voltage in a standby state, and a circuit that activates the main power supply 10a in a power-on state. The standby power supply 10b is turned on in the standby state and generates a power supply voltage. However, after the power supply is turned on and the main power supply 10a is activated, the standby power supply 10b is turned off. That is,
Standby state:
Main power supply 10a → off state standby power supply 10b → on state power on state:
Main power supply 10a → on state standby power supply 10b → off state.

  The main power supply 10a includes a rectifier circuit 14, switch elements Q1 and Q2, transformers T1 and T2, a rectifier circuit 16, and a main power supply control circuit 18.

  The rectifier circuit 14 includes a full-wave rectifier circuit, is connected to the AC plug 12, and rectifies and smoothes the input AC voltage and supplies it to the switch elements Q1 and Q2.

  Switch elements Q1 and Q2 are each composed of a MOSFET and constitute a switching circuit. The drain terminal of the switch element Q1 is connected to the positive side output of the rectifier circuit 14, the source terminal is connected to the primary side winding T1a of the transformer T1, the drain terminal of the switch element Q2 is connected, and the gate terminal is the transformer T2. Connected to the primary winding T2a. As described above, the drain terminal of the switch element Q2 is connected to the source terminal of the switch element Q1, the source terminal is connected to the negative side output of the rectifier circuit 14, and is connected to the primary side winding T2b of the transformer T2. The terminal is connected to the primary winding T2b of the transformer T2. The switch elements Q1 and Q2 operate complementarily, and when one is on, the other is off. When the switch element Q1 is on and the switch element Q2 is off, the power supply voltage from the rectifier circuit 14 is supplied to the transformer T1. The ground potential is supplied to the transformer T1 when the switch element Q1 is off and the switch element Q2 is on. The gate terminal of the switch element Q1 is connected to the primary side winding T2a of the transformer T2. The gate terminal of the switch element Q2 is connected to the primary side winding T2b of the transformer T2. Controlled by the output voltage of T2.

  The transformer T1 (main transformer) has a primary side winding T1a and secondary side windings T1b, T1c, T1d. One end of the primary winding T1a is connected to the source terminal of the switch element Q1, and the other end is connected to the connection node of the capacitors C1 and C2. The capacitors C1 and C2 are connected in series, one end of the capacitor C1 is connected to the positive output of the rectifier circuit 14, and the other end of the capacitor C2 is connected to the negative output of the rectifier circuit 14. The secondary side windings T1b and T1c are connected in series, one end of the secondary side winding T1b is connected to the rectifier circuit 16, and the other end of the secondary side winding T1c is also connected to the rectifier circuit 16. The secondary winding T1d is connected to the main power supply control circuit 18. The secondary winding T1d is connected to the set control circuit 28 via the diode D3. The set control circuit 28 will be described later.

  The transformer T2 includes primary windings T2a and T2b and a secondary winding T2c. One end of the primary winding T2a is connected to the gate terminal of the switch element Q1, and the other end is connected to the drain terminal of the switch element Q1. One end of the primary winding T2b is connected to the gate terminal of the switch element Q2, and the other end is connected to the drain terminal of the switch element Q2. The secondary winding T2c is connected to the main power supply control circuit 18. The primary side winding T2a and the primary side winding T2b are configured to have opposite polarities.

  The rectifier circuit 16 includes a full-wave rectifier circuit, is connected to the load 20, rectifies and smoothes the AC voltage from the secondary windings T1b and T1c, and supplies it as a power supply voltage to the subsequent load 20.

  The main power supply control circuit 18 is composed of a microcomputer, and controls the switching elements Q1 and Q2 by outputting a switching control signal to the secondary winding T2c of the transformer T2. The operating voltage of the main power supply control circuit 18 is supplied from the secondary winding T1d of the transformer T1 or supplied from the standby power supply 10b via the switch 30.

  The standby power supply 10b includes a rectifier circuit 22, a standby power supply control circuit 24, a transformer T3, and a standby power supply control feedback circuit 26.

  The rectifier circuit 22 includes a full-wave rectifier circuit, is connected to the AC plug 12, rectifies and smoothes the input AC voltage, and supplies it to the transformer T3.

  The standby power supply control circuit 24 includes a switch element Q3. One terminal of the switch element Q3 is connected to the primary winding T3a of the transformer T3, and the other terminal is connected to the negative output of the rectifier circuit 22. Further, a standby power control feedback circuit 26 is connected to the standby power control circuit 24 through an insulating element, and the on / off state of the switch element is controlled by a control signal from the standby power control feedback circuit 26.

  The transformer T3 (standby transformer) includes a primary side winding T3a, a tertiary side winding T3b, and a secondary side winding T3c. One end of the primary winding T3a is connected to the positive output of the rectifier circuit 22, and the other end is connected to the switch element Q3 of the standby power supply control circuit 24. The tertiary winding T3b is rectified and smoothed and connected to the standby power supply control circuit 24. The secondary winding T3c is rectified and smoothed and connected to the set control circuit 28.

  The standby power supply control feedback circuit 26 includes a photocoupler and a control circuit for energizing the LEDs of the photocoupler. The control circuit is supplied with the output voltage of the secondary winding T3c of the transformer T3 and the main power supply 10a. , More specifically, the output voltage of the secondary winding T1d of the transformer T1 is supplied via the diode D3. The standby power supply control feedback circuit 26 controls the operation of the standby power supply 10b according to the output voltage of the main power supply 10a supplied to the standby power supply 10b, that is, the output voltage of the secondary winding T1d. That is, the standby power supply control feedback circuit 26 acts to decrease the output voltage of the standby power supply 10b when the output voltage of the main power supply 10a increases, and when the output voltage of the main power supply 10a increases and exceeds the threshold, The power supply control circuit 24 stops the on / off operation of the switch element Q3 and shifts the standby power supply 10b to the off state.

  On the other hand, the switch 30 is a switch for turning on / off the connection between the main power supply control circuit 18 of the main power supply 10 a and the standby power supply 10 b, and the on / off of the switch 30 is controlled by the set control circuit 28.

  The set control circuit 28 is composed of a microcomputer, is connected to the secondary winding T3c of the transformer T3 of the standby power supply 10b, and operates by receiving an operating voltage supplied from the transformer T3 of the standby power supply 10b. The set control circuit 28 turns off the switch 30 in the standby state, and disconnects the connection between the main power supply control circuit 18 and the standby power supply 10b. The set control circuit 28 turns on the switch 30 in the power-on state, and connects the main power control circuit 18 and the standby power supply 10b.

  Next, the operation of the above configuration will be described.

<Standby state>
In the standby state, the rectifier 22 of the standby power supply unit 10b rectifies and smoothes the input AC voltage and supplies the power supply voltage to the transformer T3. The standby power supply control circuit 24 is connected to the tertiary side winding T3b of the transformer T3, and operates upon receiving a power supply voltage from the tertiary side winding T3b. The standby power supply control circuit 24 supplies a control signal that alternately repeats the Hi level and the Lo level to the gate terminal of the switch element Q3 to control the switch element Q3 on / off. When the switch element Q3 is on, the power supply voltage is supplied from the rectifier circuit 22 to the transformer T3. When the switch element Q3 is off, the power supply voltage is not supplied from the rectifier circuit 22. The transformer T3 transforms the power supply voltage, and further rectifies and smoothes it with a diode and capacitor at the subsequent stage and supplies the rectified and smoothed voltage to the set control circuit 28. The set control circuit 28 operates in response to the supply of the power supply voltage from the transformer T3.

  The set control circuit 28 controls the switch 30 to be turned off in the standby state. Therefore, the main power supply control circuit 18 of the main power supply 10a is not supplied with the power supply voltage from the standby power supply 10b, and the main power supply control circuit 18 remains off. If the main power supply control circuit 18 is in the off state, no control signal is output from the main power supply control circuit 18 to the transformer T2, and the switch elements Q1 and Q2 of the main power supply 10a remain off. Therefore, no power is supplied to the transformer T1, and the main power supply 10a remains off.

  That is, in the standby state, the main power supply 10a is in an off state, and the standby power supply 10b is in an on state.

<Power on state>
When shifting from the standby state to the power-on state, the set control circuit 28 controls the switch 30 from off to on in response to an instruction to shift to the power-on state. Then, the main power supply control circuit 18 starts operation upon receiving the supply of the power supply voltage from the standby power supply 10b. The main power supply control circuit 18 outputs a control signal to the secondary winding T2c of the transformer T2. The switch elements Q1, Q2 are on / off controlled in response to a control signal from the primary windings T2a, T2b of the transformer T2. When the switch element Q1 is on and the switch element Q2 is off, a voltage is supplied from the capacitor C1 to the transformer T1. When the switch element Q1 is off and the switch element Q2 is on, a voltage is supplied from the capacitor C2 to the transformer T1. The transformer T1 transforms the power supply voltage and supplies power to the load 20. The power supply voltage from the secondary winding T1d of the transformer T1 is rectified and smoothed and supplied to the main power supply control circuit 18. Therefore, the main power supply control circuit 18 operates by being supplied with the power supply voltage from the transformer T1 in addition to the standby power supply 10b.

On the other hand, when the switch elements Q1 and Q2 are turned on and off by a control signal from the main power supply control circuit 18 to turn on the main power supply 10a and the power supply voltage is output from the transformer T1, the output voltage from the transformer T1 is the standby power supply. This is supplied to the control feedback circuit 26.
That is, the secondary winding T1d of the transformer T1 is connected to the standby power supply control feedback circuit 26 via the diode D3, and the output voltage of the transformer T1 is supplied to the standby power supply control feedback circuit 26.

  The standby power supply control feedback circuit 26 monitors the output voltage of the transformer T1, and supplies a signal to stop the operation of the standby power supply control circuit 24 when the output voltage of the transformer T1 exceeds a threshold value.

  The standby power supply control circuit 24 receives the control signal from the standby power supply control feedback circuit 26, fixes the switch element Q3 in the OFF state, stops switching, and shifts the standby power supply 10b to the OFF state.

  Even when the standby power supply 10b is turned off, as described above, the main power supply control circuit 18 is supplied with the power supply voltage from the transformer T1, and thus can operate. The set control circuit 28 is also operable because the power supply voltage from the transformer T1 is supplied via the diode D3.

  As described above, when the power is turned on, the power supply voltage is supplied from the standby power supply 10b to the main power supply control circuit 18 to turn on the main power supply 10a. After the main power supply 10a is turned on, the standby power supply 10b is automatically turned on. When the standby power supply 10b is in the off state, the power consumption can be reduced as compared with the case where the standby power supply 10b is always on, and the influence of the noise of the standby power supply 10b itself can be eliminated.

  The standby power supply control feedback circuit 26 compares the output voltage of the main power supply 10a with a predetermined threshold value, and sets the standby power supply 10b to the standby power supply control circuit 24 when the output voltage of the main power supply 10a exceeds the threshold value. If it has a comparison circuit for comparing the output voltage of the main power supply 10a with a threshold value and a signal generation circuit for outputting a control signal according to the comparison result, an arbitrary circuit configuration can be obtained. Can be adopted.

Second Embodiment
FIG. 2 shows a switching power supply for an audio apparatus according to this embodiment. The difference from FIG. 1 is that a threshold adjustment circuit 40 is connected to the standby power supply control feedback circuit 26 of the standby power supply 10b to adjust the threshold value of the standby power supply control feedback circuit 26.

  The threshold adjustment circuit 40 is connected to the secondary winding T1d of the transformer T1 of the main power supply 10a, receives the output voltage of the transformer T1, and adjusts the threshold of the standby power supply adjustment feedback circuit 26. The threshold adjustment circuit 40 operates when the main power supply 10a is turned on and the power supply voltage is output from the transformer T1, and adjusts the threshold of the standby power supply control feedback circuit 26. As described in the first embodiment, the standby power supply adjustment feedback circuit 26 controls the standby power supply 10b from the on state to the off state when the output voltage of the transformer T1 exceeds the threshold value. Can be adjusted by the threshold adjustment circuit 40, the threshold at which the standby power supply 10b shifts from the on state to the off state or from the off state to the on state can be arbitrarily set.

  FIG. 3 shows a specific circuit configuration of the threshold adjustment circuit 40 in FIG. The threshold adjustment circuit 40 uses resistors R1, R2, and R3 that are part of the standby power supply adjustment feedback circuit. In the resistors R1, R2 and R3 connected in series, the series resistor R1 is connected to the output of the transformer T3, and the output of the primary winding T1a of the transformer T1 is connected via the diode D3. Yes. A switching element Q4 is connected in parallel with the resistor R2 between the connection node of the resistors R1 and R2 and the connection node of the resistors R2 and R3. The switch element Q4 is an npn bipolar transistor, for example, and has a collector terminal connected to a connection node between the resistors R1 and R2, an emitter terminal connected to a connection node between the resistors R2 and R3, and a base terminal connected to the Zener diode D1 and the resistor. It is connected to the anode terminal of the diode D3, that is, the secondary winding T1d of the transformer T1 via R4 and the diode D4. A connection node between the anode terminal of the diode D3 and the Zener diode D1 is a point P, and a connection node between the cathode terminal of the diode D3 and the secondary winding T3c of the transformer T3 is a point Q. The voltage Vp at the point P indicates the output voltage of the secondary side winding T1c of the transformer T1, that is, the output voltage of the main power supply 10a, and the voltage Vq at the point Q indicates the output voltage of the secondary side winding T3c of the transformer T3, That is, the output voltage of the standby power supply 10b is shown.

  A resistor and a shunt regulator Q5 connected in series with each other are connected in parallel with the resistors R1, R2, and R3. The resistor and the shunt regulator Q5 connected in series with each other constitute a standby power supply control feedback circuit 26 together with the photocoupler. The threshold value of the standby power supply control feedback circuit 26 is determined by the operating voltage of the shunt regulator Q5, and the voltage applied to the shunt regulator Q5 is determined by the resistors R1, R2, R3 and the switch element Q4. The threshold adjustment circuit 40 including the resistors R1 to R4 and the Zener diode D1 and the diode D3 adjusts the threshold for the standby power supply control feedback circuit 26 to shift the standby power supply from the on state to the off state. The

  Hereinafter, the operation of this embodiment will be described.

<Standby state>
In the standby state, the main power supply 10a is off and the standby power supply 10b is on. In this state, since the main power supply 10a is in the off state, the output voltage Vp of the main power supply 10a is at the low level, the switch element Q4 is also off, and the threshold adjustment circuit 40 is also in the off state. The standby power supply control circuit 24 controls on / off of the switch element Q3, outputs a power supply voltage from the transformer T3, and supplies it to the set control circuit 28.

<Power on state>
When shifting from the standby state to the power-on state, the set control circuit 28 turns on the switch 30. The main power supply control circuit 18 starts operation upon receiving the supply of power supply voltage from the standby power supply 10b, supplies a control signal to the switch elements Q1 and Q2 via the transformer T2, and controls on / off of the switch elements Q1 and Q2. . As a result, the main power supply 10a shifts from the off state to the on state, and the output voltage Vp of the transformer T1 increases. When the output voltage Vp of the transformer T1 increases, the base terminal of the switch element Q4 is connected to the point P via the Zener diode D1 and the resistor R4, so that a current flows through the base terminal of the switch element Q4 and the switch element Q4 From off to on. When the output voltage Vp of the transformer T1 increases, and the output voltage Vq of the standby power supply 10b increases accordingly, and exceeds the threshold value determined according to the shunt regulator Q5 of the standby power supply control feedback circuit 26, the standby power supply A control signal is output from the photocoupler of the control feedback circuit 26 and supplied to the standby power supply control circuit 24. The standby power supply control circuit 24 stops the switching operation of the switch element Q3. Thereby, the standby power supply 10b is turned off, and only the main power supply 10a operates.

  Even when the standby power supply 10b is turned off, the main power supply control circuit 18 and the set control circuit 28 are supplied with the power supply voltage of the main power supply 10a. Can be maintained as is.

<Power off state>
When shifting from the power-on state to the power-off state, the set control circuit 28 outputs a control signal to the main power supply control circuit 18 to stop the operation of the main power supply control circuit 18. When the operation of the main power supply control circuit 18 is stopped, the on / off operation of the switch elements Q1 and Q2 is stopped, and the main power supply 10a is turned off.

When the main power supply 10a is turned off, the output voltage Vp of the transformer T1 is also lowered, and the switch element Q4 is turned off from on. As the output voltage Vp of the transformer T1 decreases, the output voltage Vq of the standby power supply 10b (with the standby power supply 10b being in the off state when the power is on, the output voltage Vq is the output voltage of the main power supply 10a). It is determined)
When the voltage drops below the threshold value, the control signal is not output from the photocoupler of the standby power supply control feedback circuit 26, and the standby power supply control circuit 24 starts the on / off control of the switch element Q3 again. Thereby, the standby power supply 10b shifts from the off state to the on state.

  As described above, in the standby state, the main power source is turned off and the standby power source is turned on. In the power on state, the main power source 10a is shifted to the on state, and when the output voltage of the main power source 10a exceeds a certain value, the standby power source is turned on. 10b can be automatically turned off, and when the power supply is turned off in this state, the standby power supply 10b is automatically turned on when the output voltage of the main power supply 10a falls below a certain value. Can do.

  FIG. 4 is a circuit configuration diagram when the conventional technique is used. FIG. 4 shows a case where the general standby power supply control feedback circuit 26 in FIG. 1 is used as it is, and includes a diode D3 and resistors R1, R2 connected in series. The standby power supply 10b operates by feeding back an output obtained by rectifying and smoothing the output of the secondary side winding T3c of the transformer T3 via the standby power supply control feedback circuit 26. The anode terminal of the diode D3 is connected to the secondary winding T1d of the transformer T1, and the cathode terminal is connected to the resistor R1. Therefore, the output voltage of the transformer T1 is divided by the voltage dividing ratio of the resistors R1 and R2 and fed back.

  When shifting from the standby state to the power-on state, the set control circuit 28 controls the switch 30 to be turned on, the main power supply control circuit 18 starts operating upon receiving the supply of power supply voltage from the standby power supply 10b, and the main power supply 10a is turned on. Transition to the on state. As the output voltage of the transformer T1 increases, the output voltage Vq of the standby power supply at the point Q also increases. When the threshold value determined according to the shunt regulator Q5 is exceeded, the photocoupler of the standby power supply control feedback circuit 26 The control signal is output, the standby power supply control circuit 24 stops the on / off control of the switch element Q3, and the standby power supply 10b is turned off.

  When the power supply is switched from the power-on state to the power-off state, the main power supply 10a is turned off and the output voltage of the transformer T1 is reduced. As a result, when the output voltage Vq of the standby power supply 10b decreases to become the threshold value or less, the standby power supply control circuit 24 similarly resumes the on / off control of the switch element Q3, and the standby power supply 10b is turned on.

  In this example, there is an advantage that the switch element Q4 is unnecessary and the configuration is simple. On the other hand, when the output voltage of the transformer T1 of the main power supply 10a increases and becomes equal to or higher than the output voltage of the standby power supply 10b. Since the voltage division determined by the voltage dividing ratio of the resistors R1 and R2 can exceed the threshold value, the standby power supply 10b remains on and automatically turns off while the output voltage of the transformer T1 falls below the output voltage of the standby power supply 10b. Do not move to. On the other hand, in the configuration of FIG. 3, since the on / off of the switching element Q4 is controlled by the output voltage Vp of the transformer T1 of the main power supply 10a, even if the output voltage of the transformer T1 is lower than the output voltage of the standby power supply 10b. The standby power supply 10b can be shifted from the on state to the off state at a desired voltage.

  Further, in the configuration of FIG. 4, when the output voltage of the main power supply 10a is lowered for some reason, for example, the AC voltage itself input from the AC plug 12 fluctuates and falls below the original voltage (hereinafter referred to as “power reduction”). Even if the main power supply 10a is in the on state, the output voltage Vq of the standby power supply 10b becomes equal to or less than the threshold value, and the standby power supply control circuit 24 resumes the on / off control of the switch element Q3 to bring the standby power supply 10b from the off state. It will be shifted to the on state. In this case, since both the main power supply 10a and the standby power supply 10b are turned on, the noise of the standby power supply 10b itself can be a problem.

  On the other hand, in the configuration of FIG. 3, even when the input voltage is reduced, the standby power supply 10b can be maintained in an off state up to a desired voltage. That is, when the main power supply 10a is in the on state and the standby power supply 10b is in the off state, and the power supply voltage decreases in this state, the output voltage Vp of the transformer T1 of the main power supply 10a decreases and the output voltage Vq However, if the switch element Q4 remains on, the standby power supply control circuit 24 does not perform the on / off control of the switch element Q3, and can maintain the standby power supply 10b in the off state. When the output voltage Vp of the transformer T1 of the main power supply 10a further decreases, and the output voltage Vq further decreases below the threshold value, the switch element Q4 is turned off and the standby power supply control circuit 24 The on / off control of Q3 is resumed to shift the standby power supply 10b from the off state to the on state.

  In addition, the standby power supply 10b can be shifted from the off state to the on state when the standby power supply 10b is more actively lowered to a desired voltage instead of maintaining the off state when the power is reduced. The set control circuit 28 operates in response to the supply of the power supply voltage from the main power supply 10a in the power-on state, but the output voltage of the standby power supply 10b is also supplied to the set control circuit 28. Therefore, when the power supply voltage from the main power supply 10a is reduced and the supply voltage to the set control circuit 28 is insufficient due to a decrease in input voltage, the standby power supply 10b is switched from the off state to the on state at an appropriate timing. If shifted, the output voltage of the standby power supply 10b can be supplied to the set control circuit 28, and the operation of the set control circuit 28 can be stabilized. That is, when the problem that the supply voltage to the set control circuit 28 constituted by the microcomputer rather than the noise of the standby power supply 10b decreases and the operation becomes unstable becomes apparent, the main power supply 10a When the standby power supply 10b is shifted from the OFF state to the ON state and the output voltage of the standby power supply 10b is supplied to the set control circuit 28 when the voltage drops to the level, the set control circuit 28 can be stably operated. In this sense, the circuit configuration of FIG. 3 can prevent noise of the standby power supply 10b, and if necessary at the time of power reduction, the standby power supply 10b is shifted to an on state to enable stable operation of the audio apparatus. It can be said that there is an effect.

  10a main power supply, 10b sub power supply, 12 AC plug, 14, 16, 22 rectifier circuit, 20 load, 24 main power supply control circuit, 26 standby power supply control feedback circuit, 28 set control circuit, 30 switch, 40 threshold adjustment circuit.

Claims (3)

Main transformer,
A switching element provided on the primary side of the main transformer, for switching power supplied to the main transformer;
A main power supply control circuit which is provided on the secondary side of the main transformer and which controls the switch element on and off;
A main power supply comprising:
A standby transformer,
A standby power supply control circuit that is provided on a primary side of the standby transformer and that switches power supplied to the standby transformer;
A standby power control feedback circuit that is provided on the secondary side of the standby transformer and controls the operation of the standby power control circuit according to the output of the main power;
A standby power supply comprising:
A switch for turning on and off the connection between the main power supply control circuit and the standby transformer of the standby power supply;
A set control circuit that is provided on the secondary side of the standby transformer and controls the switch on and off;
With
In the standby state, the standby power supply control circuit is in an operating state to supply power from the standby transformer to the set control circuit, and the set control circuit controls the switch off to control the main power supply control circuit and the When the main power supply is in an operation stop state and the power supply is in an on state, the set control circuit controls the switch to turn on to supply power from the standby transformer to the main power supply control circuit to thereby supply the main power supply control circuit and the main power supply. The switching power supply is characterized in that power is output from the main transformer in an operating state, and the standby power control feedback circuit puts the standby power control circuit into a stopped state in accordance with the output from the main transformer. The switching power supply according to claim 1,
The standby power supply control feedback circuit is in a power-on state, and when the output of the main power supply exceeds a threshold value, the standby power supply control circuit is stopped.
A threshold adjustment circuit connected to the standby power supply control feedback circuit and setting the threshold to a predetermined value;
A switching power supply comprising: The switching power supply according to claim 1 or 2,
When the power is on and the power input is reduced, the standby power control feedback circuit activates the standby power control circuit according to the power output from the main transformer, and the standby power control circuit A switching power supply characterized by maintaining power supply from a transformer to the set control circuit and the main power supply control circuit.

Images