JP2009201330A - Switching power-supply circuit - Google Patents

Abstract

In a switching power supply circuit provided in an electronic device without an AC switch and provided with a control circuit, power consumption is reduced while power supply to the control circuit is maintained when a power supply of a secondary circuit is off.
DC power output from a capacitor C1 that smoothes a DC voltage obtained by full-wave rectifying an AC voltage from an AC power supply is supplied to a control IC 53 via resistors R2, R3, and R4. In addition to the first path, the second path through which the DC power output from the diode D1 for half-wave rectifying the AC voltage from the AC power source is supplied to the control IC 53 via the resistor R1, and the auxiliary power source monitoring A circuit 51. When the auxiliary power supply monitoring circuit 51 generates a voltage in the auxiliary power supply 55, the first path is energized and the second path is electrically cut off, and no voltage is generated in the auxiliary power supply 55. In addition, the first path is electrically cut off and the second path is energized.
[Selection] Figure 1

Description

  The present invention relates to a switching power supply circuit.

  Generally, a switching power supply circuit includes a primary side circuit connected to an AC power supply, a secondary side circuit connected to a load side, and a transformer. The primary winding of the transformer is provided in the primary side circuit, and the secondary winding of the transformer is provided in the secondary side circuit. The primary side circuit may further include an auxiliary winding of the transformer. As a switching power supply circuit having an auxiliary winding, for example, a circuit disclosed in Patent Document 1 is known. According to the circuit disclosed in Patent Document 1, when a voltage is generated in the auxiliary winding, the power loss due to the starting resistance is hardly generated.

JP 2000-175449 A

  In general, a switching power supply circuit having an auxiliary winding generates a voltage in the auxiliary winding when the power of the secondary circuit is on, and a voltage in the auxiliary winding when the power of the secondary circuit is off. It has a configuration that does not occur. Therefore, according to Patent Document 1, it is possible to reduce power consumption when the power supply of the secondary side circuit is on.

  However, it may be desirable to reduce power consumption when the secondary circuit power is off. Specifically, a switching power supply circuit including an auxiliary winding is mounted on an electronic device without an AC switch for controlling on / off of a commercial AC power supply, and controls power supply to the primary winding. A circuit (for example, IC (Integrated Circuit)) may be provided in the primary circuit. In this switching power supply circuit, the DC power obtained by converting the AC power from the commercial AC power supply is continuously supplied to the control circuit through the resistor regardless of whether the power supply of the secondary circuit is on or off. become. Therefore, it is desirable to reduce power consumption at least when the power supply of the secondary circuit is off. On the other hand, even if the power supply of the secondary side circuit is off, it is necessary to continue to supply the control circuit with power for starting up when the power supply of the secondary side circuit is turned on.

  Accordingly, an object of the present invention is to reduce power consumption while maintaining power supply to a control circuit in a switching power supply circuit provided in an electronic device without an AC switch and provided with a control circuit when the power supply of the secondary circuit is off. There is to do.

  The primary side circuit of the switching power supply circuit is a first rectifying means for full-wave rectifying the AC voltage from the AC power supply to convert it into a DC voltage, and a smoothing means for smoothing the DC voltage output from the first rectifying means. In addition to the first path through which the DC power output from the smoothing means is supplied to the control circuit via the first resistor, the AC voltage from the AC power source is rectified and converted to a DC voltage. A second rectifier, a second path through which non-smooth DC power output from the second rectifier is supplied to the control circuit via a second resistor, and an auxiliary power monitoring circuit. Prepare. The auxiliary power supply monitoring circuit energizes the first path when the auxiliary power supply (the power supply circuit that supplies the power generated in the auxiliary winding to the control circuit) has a voltage of a predetermined value or more, and the second power supply When the auxiliary power supply does not generate a voltage exceeding a predetermined value, the first path is electrically blocked and the second path is energized.

  The auxiliary power supply monitoring circuit includes, for example, a plurality of switch means. The switch means is, for example, a switching element. The plurality of switching elements include a first switching element for controlling energization / cutoff of the first path, a second switching element for controlling energization / cutoff of the second path, and an auxiliary power source. A third switching element that is turned on / off depending on whether or not a voltage greater than a predetermined value is generated. The auxiliary power supply monitoring circuit turns on the first switching element and turns off the second switching element when the third switching element is on, and turns off the first switching element when the third switching element is off. Is turned off and the second switching element is turned on. In this case, the “voltage not lower than a predetermined value” is a voltage having a value necessary for turning on the third switching element.

  FIG. 1 shows a separately excited oscillation type switching power supply circuit according to an embodiment of the present invention.

  This separately excited oscillation type switching power supply circuit is an ON / OFF type power supply circuit. This power supply circuit can be mounted on an electronic device without an AC switch for controlling on / off of a commercial AC power supply. This power supply circuit includes a primary circuit 501 connected to the commercial power supply 101, a secondary circuit 503 connected to a load (not shown), and a transformer 4. The primary side circuit 501 is provided with a primary winding 4 a and an auxiliary winding 4 c of the transformer 4, and the secondary side circuit 503 is provided with a secondary winding 4 b of the transformer 4. The anode terminal of the rectifying diode D2 is connected to one end of the secondary winding 4b, and the high potential side output terminal of the capacitor C3 is connected to the cathode terminal of the diode D2.

  Although not shown, the secondary circuit 503 is provided with a power switch for the secondary circuit 503 (hereinafter referred to as a secondary power switch). When the secondary side power switch (for example, the main power switch provided in the electronic device equipped with the switching power circuit of FIG. 1) is on, a voltage is generated in the auxiliary winding 4c, and when it is off, the auxiliary power switch No voltage is generated in the winding 4c.

The primary circuit 501 has an EMI (electromagnetic)
(immunity) filter circuit 1, diode bridge 2, smoothing capacitor C 1, MOS FET (Metal Oxide Semiconductor Field Effect Transistor) 61, control IC 53, auxiliary power supply 55, and auxiliary power supply monitoring circuit 51.

  The EMI filter circuit 1 is connected to the commercial power supply 101 and is a filter for suppressing EMI noise.

  The diode bridge 2 performs full-wave rectification on the AC voltage from the commercial power supply 101 via the EMI filter circuit 1. The smoothing capacitor C1 is connected between both output terminals of the diode bridge 2, and smoothes (stores) the DC power after full-wave rectification.

  The drain terminal of the MOS FET 61 is connected to one end of the primary winding 4 a of the transformer 4, and the gate terminal is connected to the secondary output voltage control terminal (hereinafter referred to as OUT terminal) of the control IC 53.

  The control circuit IC53 includes, for example, a first power supply terminal (hereinafter referred to as VH terminal), a second power supply terminal (hereinafter referred to as VCC terminal), an OUT terminal, a power limit input terminal (hereinafter referred to as IS terminal), and a voltage control signal input terminal. (Hereinafter referred to as FB terminal). The VH terminal is a terminal to which a DC voltage obtained by rectifying an AC voltage from a commercial power supply is input, and a first path and a second path described later are connected to the VH terminal. The VCC terminal is a terminal to which a DC voltage from the auxiliary power supply 55 is input, and a high potential side output terminal of the capacitor C3 in the auxiliary power supply 55 is connected to the VCC terminal. The OUT terminal is a terminal from which a voltage signal (voltage signal input to the gate terminal of the MOS FET 61) for controlling power supply to the primary winding 4a (power supply to the secondary circuit 503) is output. . The IS terminal is a terminal to which the DC power output from the smoothing capacitor C1 is input via a fourth transistor Tr4 and resistors R3 and R4, which will be described later. The voltage control signal from the photocoupler 7 is input to the FB terminal. The photocoupler 7 is provided in a voltage detection circuit (not shown). The voltage detection circuit uses the voltage across the capacitor C2 for stabilizing the secondary output voltage (the capacitor C2 to which the induced current from the secondary winding 4b is input via the diode D2) as the secondary output voltage of the transformer 4. As a circuit to be monitored. A voltage control signal according to the monitoring result is output from the photocoupler 7. The collector terminal of the phototransistor constituting the photocoupler 7 is connected to the FB terminal of the control IC 53, and the emitter terminal is connected to the low potential side output terminal of the diode bridge 2.

  The auxiliary power supply 55 is a power supply circuit including an auxiliary winding 4c, a backflow prevention diode D3, and a capacitor C2. The anode terminal of the backflow prevention diode D3 is connected to one end of the auxiliary winding 4c, and the cathode terminal is connected to the VCC terminal. The high potential side output end of the capacitor C3 is connected to the VCC terminal, and the low potential side output end is connected to the low potential side output end of the diode bridge 2 and the other end of the auxiliary winding 4c. With this configuration, when a voltage is generated in the auxiliary winding 4c, the capacitor C3 is charged via the backflow prevention diode D3, and the DC voltage (for example, 20V) lower than the DC voltage (for example, 140V) from the capacitor C1 is charged from the capacitor C3. ) Is input to the VCC terminal.

  The auxiliary power supply monitoring circuit 51 is a circuit that monitors whether or not a voltage is generated in the auxiliary power supply 55 (that is, the auxiliary winding 4c). Specifically, for example, the auxiliary power monitoring circuit 51 includes first to fourth bipolar transistors Tr1 to Tr4 (other types of switching elements may be employed instead of the bipolar transistors).

  The first transistor Tr1 is a transistor that is turned on / off depending on whether or not a voltage of a predetermined value or higher is generated in the auxiliary power supply 55. When the voltage is generated in the auxiliary winding 4c, the power output from the auxiliary power supply 55 is supplied to the base terminal of the first transistor Tr1. The collector terminal of the first transistor Tr 1 is connected to the base terminals of the second transistor Tr 2 and the third transistor Tr 3, and the emitter terminal is connected to the low potential side output terminal of the diode bridge 2. Therefore, when the first transistor Tr1 is on, the second and third transistors Tr2 and Tr3 are off, respectively. When the first transistor Tr1 is off, the second and third transistors Tr2 and Tr3 are respectively off. Is on.

  The second transistor Tr2 is a transistor for controlling energization / cutoff of the second path. When the second transistor Tr2 is on, the second path is energized, and when the second transistor Tr2 is off, the second path is electrically cut off. Here, the “second route” is a route connected from the live side route of the commercial power supply 101 to the VH terminal of the control IC 53. In the second path, from the upstream side (commercial power supply 101 side) to the downstream side (control IC 53 side), a diode D1 for half-wave rectifying the AC voltage from the commercial power supply 101 through the EMI filter circuit 1, and a resistor There is R1 and a second transistor Tr2. The anode terminal of the diode D1 is connected to one input end of the diode bridge 2, and the cathode terminal is connected to one end of the resistor R2. The collector terminal of the second transistor Tr2 is connected to the other end of the resistor R1, and the emitter terminal is connected to the VH terminal of the control IC 53.

  The third transistor Tr3 is a transistor for controlling on / off of the fourth transistor Tr4. The collector terminal of the third transistor Tr3 is connected to the base terminal of the fourth transistor Tr4, and the emitter terminal is connected to the low potential side output terminal of the diode bridge 2.

  The fourth transistor Tr4 is a transistor for controlling energization / cutoff of the first path. When the fourth transistor Tr4 is on, the first path is energized, and when the fourth transistor Tr4 is off, the first path is electrically cut off. Here, the “first path” is a path connected from the high potential side output terminal of the smoothing capacitor C1 to the control IC 53. A fourth transistor Tr4 exists in the first path. On the downstream side, the first sub path is connected from the emitter terminal of the fourth transistor Tr4 to the VH terminal via the resistor R2, and from the emitter terminal of the fourth transistor Tr4 to the IS terminal via the resistors R3 and R4. Branches to the second sub-path (the collector terminal of the fourth transistor Tr4 is connected to the high-potential side output terminal of the smoothing capacitor C1). Resistors R3 and R4 are connected in series. One end of each of the resistors R2 and R3 is connected to the emitter terminal of the fourth transistor Tr4. The other end of the resistor R2 is connected to the VH terminal. The other end of the resistor R3 is connected to one end of the resistor R4, and the other end of the resistor R4 is connected to the IS terminal.

  Hereinafter, an operation performed in the switching power supply circuit shown in FIG. 1 will be described.

  When a secondary power switch (not shown) is turned on, a voltage is generated in the auxiliary winding 4c, and the first transistor Tr1 is turned on from the auxiliary power supply 55 to the base terminal of the first transistor Tr1. Necessary power is supplied. Therefore, the first transistor Tr1 is turned on. Further, a DC voltage (for example, 20 V) lower than the DC voltage (for example, 140 V) from the smoothing capacitor C1 is input from the auxiliary power supply 55 to the VCC terminal.

  When the first transistor Tr1 is turned on, the second and third transistors Tr2 and Tr3 are turned off, and the fourth transistor Tr4 is turned on. As a result, the second path passing through the resistor R1 is blocked, and the first path having the resistance R2 connected to the VH terminal and the resistances R3 and R4 connected to the IS terminal is energized. For this reason, the DC power smoothed from the smoothing capacitor C1 is supplied to the control IC 53 via the resistor R2 and the resistors R3 and R4.

  As a result, when the secondary power switch is on, the control IC 53 receives the power supply from the smoothing capacitor C1 via the first path and the power supply from the auxiliary power supply 55, and supplies the power to the primary winding 4a. (Specifically, by switching the MOS FET 61 via the OUT terminal and controlling the switching frequency, the effective amount of current supplied to the primary winding 4a can be reduced. Can be controlled).

  On the other hand, when the secondary side power switch (not shown) is turned off, no voltage is generated in the auxiliary winding 4c, and the first transistor Tr1 is connected to the base terminal of the first transistor Tr1 from the auxiliary power supply 55. The power required to turn on is not supplied. Therefore, the first transistor Tr1 is turned off.

  When the first transistor Tr1 is turned off, the second and third transistors Tr2 and Tr3 are turned on, and the fourth transistor Tr4 is turned off. As a result, the second path passing through the resistor R1 is energized, and the first path having the resistor R2 connected to the VH terminal and the resistors R3 and R4 connected to the IS terminal is blocked. For this reason, DC power obtained by half-wave rectifying AC power from the commercial power supply 101 via the EMI filter circuit 101 is supplied to the VH terminal of the control IC 53 via the resistor R1.

  As a result, when the secondary power switch is off, the control IC 53 receives power supplied via the second path (receives half-wave rectified DC power) and can maintain the standby state. it can.

  As described above, according to the above-described embodiment, when the secondary side power switch is OFF, the AC power from the commercial power source 101 is replaced with the half-wave rectified and smoothed DC power by the AC power from the commercial power source 101. Wave rectified and non-smooth DC power is supplied (for example, voltage supply with a period of 50 Hz or 60 Hz). As a result, power consumption when the secondary power switch is off can be reduced. In the second path, even if a full-wave rectifier is employed instead of the half-wave rectifier such as the diode D1, power consumption can be expected to be reduced, but preferably a half-wave rectifier is employed. .

  As mentioned above, although embodiment of this invention was described, this embodiment is only the illustration for description of this invention, and is not the meaning which limits the scope of the present invention only to this embodiment. The present invention can be implemented in various other modes without departing from the gist thereof. The switching power supply circuit according to the present invention can be mounted on various electronic devices such as a printer.

1 shows a configuration example of a separately excited oscillation type switching power supply circuit according to an embodiment of the present invention.

Explanation of symbols

2 ... Rectifier circuit 51 ... Auxiliary power supply monitoring circuit 53 ... Control IC 55 ... Auxiliary power supply R1, R2, R3, R4 ... Resistors C1, C2, C3 ... Capacitors D1, D2, D3 ... Diodes Tr1, Tr2, Tr3, Tr4 ... Bipolar Transistor

Claims (2)

In a switching power supply circuit mounted on an electronic device without an AC switch for controlling on / off of the AC power supply,
A primary circuit connected to an AC power source;
A secondary circuit connected to the load side;
A transformer having a primary winding and an auxiliary winding provided in the primary side circuit, and a secondary winding provided in the secondary side circuit;
When the secondary circuit power is off, no voltage is generated in the auxiliary winding, and when the secondary circuit power is on, a voltage is generated in the auxiliary winding,
The primary circuit is
A control circuit;
An auxiliary power supply that is a power supply circuit that supplies power generated in the auxiliary winding to the control circuit;
A first rectifying means for converting the AC voltage from the AC power source into a DC voltage by full-wave rectification;
Smoothing means for smoothing the DC voltage output from the first rectifying means;
A second rectifying means for rectifying an AC voltage from the AC power source and converting the AC voltage into a DC voltage;
A first path through which the DC power output from the smoothing means is supplied to the control circuit via a first resistor;
A second path through which the non-smooth DC power output from the second rectifier is supplied to the control circuit via a second resistor;
When a voltage of a predetermined value or more is generated in the auxiliary power supply, the first path is energized and the second path is electrically cut off, and a voltage of a predetermined value or more is generated in the auxiliary power supply. An auxiliary power supply monitoring circuit that electrically shuts off the first path and energizes the second path when not
Switching power supply circuit. The second rectifying means is means for half-wave rectifying the AC power.
The switching power supply circuit according to claim 1.

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