JP2008289334A - Switching power supply device, and power supply control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply device capable of reducing power consumption efficiently during a power saving mode with a small number of parts. <P>SOLUTION: A switch element (FET) 3 is a semiconductor switch for reducing uselessly consumed power by a power factor improving circuit 100 during a power saving mode of load, and is connected between an output terminal of a rectification circuit 2 and an output terminal of a power factor improving circuit 100 so as to bypass the power factor improving circuit 100. The control circuit 300 sets the switch element (FET) 3 to an off state when an output current of a DC/DC converter 200 is a prescribed amount or larger (when a load is in a normal mode), and the switch element (FET) 3 to an on state when the output current is less than the prescribed amount (when a load is in a power saving mode). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a switching power supply device for generating electric power to be supplied to an electronic device and a power supply control method for controlling the power supply device.

  Generally, in a switching power supply device, a capacitor input type smoothing circuit is used. The DC voltage smoothed by the capacitor input type smoothing circuit is converted into a desired DC voltage by a switching DC / DC converter such as a switching regulator and then supplied to the load.

  In addition, in a switching power supply device using a capacitor input type smoothing circuit, a power factor improvement composed of a boost regulator or the like is provided between the rectifier circuit and the input smoothing capacitor in order to improve the power factor. A circuit is provided.

  However, in the conventional switching power supply device equipped with the power factor correction circuit, the current from the rectifier circuit is always switched via the power factor correction circuit even when the electronic device as the load is in the power saving mode. / Flows to DC converter. For this reason, even in the power saving mode that does not require power factor correction, power is wasted by the inductors and diodes in the power factor correction circuit.

  Accordingly, several techniques for reducing the power consumption of the power factor correction circuit have been proposed. For example, in Patent Documents 1 and 2, two first and second rectifier circuits and a switch for connecting an AC power supply to one of these two rectifier circuits are provided. AC power supply → first rectifier circuit → power A power supply path that passes through the power factor correction circuit, such as a rate improvement circuit → smoothing capacitor, and a power supply path that does not go through the power factor correction circuit, such as an AC power source → second rectifier circuit → smoothing capacitor, are selectively used. A switching power supply device is disclosed.

Further, Patent Document 3 discloses a switching power supply device that stops the power factor correction function in the power saving mode.
JP 2005-39922 A JP 11-136858 A JP 2005-168146 A

  However, in the configuration of the switching power supply as disclosed in Patent Document 1 and Patent Document 2, a rectifier is required for each of the two power supply paths, and a dedicated switch for switching between the two power supply paths is also provided. There is a problem that the number of parts is increased.

  Moreover, since the switching power supply device as disclosed in Patent Document 3 stops the power factor correction control function in the power saving mode, the current consumption can be reduced accordingly. However, since a power factor correction circuit is included in the power supply path, a minute current flows through inductors and diodes in the power factor correction circuit, and unnecessary power is consumed accordingly. was there.

  The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide a switching power supply apparatus and a power supply control method capable of efficiently reducing power consumption in a power saving mode with a small number of parts. And

  In order to solve the above-described problems, a switching power supply device according to the present invention includes a power factor correction circuit connected to an output terminal of a rectifier circuit that rectifies an input AC voltage, and a smoothing capacitor connected to an output terminal of the power factor correction circuit. The switching type DC / DC converter which converts the input DC voltage into a predetermined DC voltage to be supplied to the load by switching the first switch element and bypassing the power factor correction circuit Detecting the output current of the second switch element connected between the output terminal of the rectifier circuit and the output terminal of the power factor correction circuit, and the DC / DC converter supplied to the load, When the output current is greater than or equal to a predetermined value, the second switch element is set to an off state, and when the output current is less than the predetermined value, the second switch element is turned off. Characterized by comprising a control circuit for setting the state.

  In the present invention, the DC / DC converter is connected to a transformer, a primary side of the transformer, an input circuit unit including the first switch element, and a smoothing connected to the primary side of the transformer. A switching control circuit that is driven by a power supply voltage supplied from the control circuit and controls the switching of the first switch element according to the value of the output voltage of the DC / DC converter, and is connected to the secondary side of the transformer An output smoothing circuit, and the power factor correction circuit includes a switching booster circuit including a third switch element and a power supply voltage supplied from the smoothing circuit connected to the primary side of the transformer. A power factor correction control circuit that is driven to control the switching of the third switch element, and is connected between the output terminal of the smoothing circuit and the power factor correction control circuit And the control circuit sets the fourth switch element to an ON state when the output current is greater than or equal to a predetermined value, and the output current is less than the predetermined value. In this case, the fourth switch element is set in an off state.

  According to the present invention, it is possible to efficiently reduce power consumption in the power saving mode with a small number of parts.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a configuration of a switching power supply device according to an embodiment of the present invention will be described with reference to FIG.

  The switching power supply device is used as a power supply device for various electronic devices such as personal computers and AV equipment. In this case, the switching power supply device can be realized as a form incorporated in an electronic device or as an external AC adapter. This switching power supply device is for generating DC power to be supplied from an AC power supply 1 to a load, and includes a rectifier circuit 2, a power factor correction circuit 100, a smoothing capacitor 8, a DC / DC converter 200, a switch element 3 ( The second switch element), the control circuit 300, and the like.

  The rectifier circuit 2 rectifies the input AC voltage from the AC power source 1. The output terminal of the rectifier circuit 2 is connected to a power factor correction circuit 100 including a switching type booster circuit. A DC / DC converter 200 is connected to the output terminal of the power factor correction circuit 100 via the smoothing capacitor 8. The DC / DC converter 200 is a switching DC / DC converter that converts a DC voltage input through the smoothing capacitor 8 into a predetermined DC voltage to be supplied to a load by switching control of an internal switch element. It is a DC converter. A load is connected to the positive output terminal 13 and the negative output terminal 14 of the DC / DC converter 200.

  The switch element 3 is a semiconductor switch for reducing wasted power consumed by the power factor correction circuit 100 in the power saving mode of the load. The switch element 3 is connected to the output terminal of the rectifier circuit 2 so as to bypass the power factor correction circuit 100. It is connected between the output terminal of the power factor correction circuit 100. The switch element 3 is composed of, for example, an FET, and one end of the current path between the drain and source thereof is connected to the output end of the rectifier circuit 2, and the other end is connected to the output end of the power factor correction circuit 100.

  The control circuit 300 detects the output current of the DC / DC converter 200 using the current detection resistor 12 connected to the output of the DC / DC converter 200, and according to the detected output current value, the switch element ( FET) 3 is set to an off state or an on state. That is, as shown in FIG. 2, when the output current is equal to or greater than a predetermined value (when the load is in the normal mode), the control circuit 300 sets the switch element (FET) 3 to the OFF state and the output current is predetermined. When the value is smaller than the value (when the load is in the power saving mode), the switch element (FET) 3 is set to the ON state. When the switch element (FET) 3 is turned on, the output of the rectifier circuit 2 is directly connected to the smoothing capacitor 8 via the switch element (FET) 3. For this reason, almost no current flows through the power factor correction circuit 100, and the power consumption of the power factor correction circuit 100 in the power saving mode can be greatly reduced.

  Next, an example of a specific circuit configuration of the switching power supply device according to the present embodiment will be described with reference to FIG.

  In the switching power supply device of FIG. 3, the rectifier circuit 2 is composed of a bridge diode. The power factor correction circuit 100 includes an inductor 4, an FET 5 (third switch element), a diode 6, and a power factor correction control circuit 7. The power factor correction control circuit 7 switches the FET 5 to generate an output voltage higher than the voltage from the rectifier circuit 2. The power factor correction control circuit 7 is driven by a power supply voltage supplied from a smoothing circuit (diode 21 and capacitor 22) connected to the primary side of the transformer 9.

  The DC / DC converter 200 is an insulating switching regulator, and includes a transformer 9, an input circuit unit connected to the primary side of the transformer 9, and an output smoothing circuit (diode 10) connected to the secondary side of the transformer. , Capacitor 11) and the like. In the input circuit section, an FET (first switch element) 16 is provided. The FET (first switch element) 16 is switching-controlled by a switching control signal (PWM signal) from a pulse width modulation (PWM) control circuit 20. The PWM control circuit 20 performs switching control of the FET (first switch element) 16 according to the output voltage value of the DC / DC converter 200 detected by the voltage detection circuit 400 realized using a photocoupler or the like. This is a switching control circuit. The on-duty ratio of the PWM signal output from the PWM control circuit 20 is variably controlled according to the difference value between the output voltage of the DC / DC converter 200 and the reference voltage value. The PWM control circuit 20 is also driven by the power supply voltage supplied from the smoothing circuit (diode 21 and capacitor 22) connected to the primary side of the transformer 9, as with the power factor correction control circuit 7.

  The PWM control circuit 20 is directly connected to the output terminal of the smoothing circuit (diode 21 and capacitor 22). It is connected to the output terminal of the circuit (diode 21, capacitor 22). The PNP transistor (fourth switch element) 17 functions as a circuit for cutting off power supply to the power factor correction control circuit 7 in the power saving mode.

  The photocoupler 23, the error amplifier 24, and the operational amplifier 25 function as the control circuit 300 in FIG. The operational amplifier 25 is a detection circuit that detects the voltage across the current detection resistor 12. The error amplifier 24 compares the voltage detected by the operational amplifier 25 with the reference voltage 26 and outputs a signal corresponding to the difference value. The photocoupler 23 includes a light emitting diode 27 and a phototransistor 28. The collector of the phototransistor 28 is connected to the gate of the FET 3 and is connected to the base of the transistor 17 via the resistor 18. A resistor 19 is connected between the base and emitter of the transistor 17.

  In response to the output signal from the error amplifier 24, the photocoupler 23 sets the FET 3 to the off state and sets the transistor 17 to the on state when the output current of the DC / DC converter 200 is a predetermined value or more. The second value for setting the FET 3 to the on state and setting the transistor 17 to the off state when the output signal of the first value is less than the predetermined value. The control signal is output.

  Here, the operation in the power saving mode of the switching power supply device of FIG. 3 will be described with reference to the timing chart of FIG.

  4 shows the signal of the diode 27 inside the photocoupler 23, the collector-emitter voltage of the transistor 28 inside the photocoupler 23, the collector current of the transistor 28, the collector-emitter voltage of the transistor 17, the transistor 17 The transition of the collector current, the drain-source voltage of FET3, and the drain current of FET3 is shown.

  In the power saving mode, the current flowing through the current detection resistor 12 is reduced, and the potential difference between both ends of the current detection resistor 12 is also reduced. For this reason, the output of the operational amplifier 25 becomes smaller than the reference voltage 26, and the output of the error amplifier 24 becomes a negative value. As a result, the diode 27 inside the photocoupler 23 does not emit light, the transistor 28 inside the photocoupler 23 is turned off, and the collector current of the transistor 28 becomes zero.

  When the transistor 28 in the photocoupler 23 is turned off, the base current of the transistor 17 is not drawn, so that the transistor 17 is turned off and the collector current of the transistor 17 becomes zero. Thereby, power supply from the smoothing circuit (diode 21 and capacitor 22) to the PWM control circuit 20 is maintained, but power supply from the smoothing circuit (diode 21 and capacitor 22) to the power factor correction control circuit 7 is maintained. When stopped, the power factor correction control circuit 7 stops its operation.

  Further, when the transistor 28 in the photocoupler 23 is turned off, a positive voltage is applied to the gate of the FET 3 and the FET 3 is turned on. When the FET 3 is turned on, in addition to the path of rectifier circuit 2 → inductor 4 → diode 6 → smoothing capacitor 8 (referred to as path 1), a path of rectifier circuit 2 → FET 3 → smoothing capacitor 8 (referred to as path 2) is formed. .

Conventionally, since there is no path 2, if the winding resistance of the inductor 4 is RL, the forward voltage of the diode 6 is Vrm, and the current flowing through the diode 6 is Iprms, the power consumption by the power factor correction circuit 100 is
RL × Iprms ² + Vrm × Iprms
It was. Further, when the resistance Rrm of the diode 6 is obtained,
Vrm / Iprms
Thus, when Iprms << Vrm, Rrm was a considerably large value.

However, in the present embodiment, since there is a path 2 in parallel with the path 1, if the ON resistance of the FET 3 is Ron, the current flowing through the FET 3 is Idrms, and the leakage current flowing through the inductor 4 and the diode 6 is IdLDrms, the power consumption is
Ron × Idrms ² + RL × IdLrms ²
+ (Ron * Idrms-RL * IdLDrms) * IdLDrms
It becomes. Note that (Ron × Idrms−RL × IdLDrms) is a voltage across the diode 6 when the path 2 exists. Therefore,
(RL × Iprms ² + Vrm × Iprms)
− (Ron × Idrms ² + RL × IdLDrms ²
+ (Ron * Idrms-RL * IdLDrms) * IdLDrms)
Power is reduced.

  Further, since the power factor correction control circuit 7 is also stopped, further power saving can be realized.

When RL = 0.05Ω, Iprms = 30 mA, Vrm = 0.6 V, Ron = 0.5Ω, IdLDrms = 0.1 mA, the power consumption of the conventional configuration of only path 1 is
RL × Iprms ² + Vrm × Iprms
= 0.05Ω × (30 mA) ² +0.6 V × 30 mA
= 18.04mW
It becomes. The power consumption in this embodiment in which there is a route 2 in addition to the route 1 is
Ron × Idrms ² + RL × IdLrms ²
+ (Ron * Idrms-RL * IdLDrms) * IdLDrms
= 0.5Ω × (30 mA-0.1 mA) ² + 0.05Ω × (0.1 mA) ²
+ (0.5Ω × (30 mA−0.1 mA) −0.05Ω × 0.1 mA) × 0.1 mA
^{= 0.5Ω × (29.9mA) 2 +} 0.05Ω × (0.1mA) 2 + (0.5Ω × 29.9mA-0.05Ω × 0.1mA) × 0.1mA
= 0.4485mW
It becomes. 18.04 mW−0.4485 mW = 17.59 mW of power can be reduced.

  Therefore, the power consumption can be reduced by 17.59 mW / 18.04 mW × 100 = 97.5%.

  As described above, in the present embodiment, the FET 3 that is a semiconductor switch is turned on only in the power saving mode and the path 2 is enabled. Therefore, in the normal mode, the output of one rectifier 2 is passed through the path 1. In the power saving mode, the output of one rectifier 2 can be directly transferred to the smoothing capacitor 8 via the path 2. Therefore, compared to the conventional configuration using two rectifiers and a dedicated changeover switch, the number of parts can be reduced, and cost reduction and space saving can be realized. Further, since the FET 3 that is a semiconductor switch is used for path switching, smooth switching can be realized without worrying about momentary power failure. Further, in the power saving mode, not only the FET 3 is turned on but also the transistor 17 is turned off and the power supply to the power factor correction control circuit 7 is stopped, so that further power saving can be realized.

  Note that the switching power supply device of the present embodiment can be used as, for example, an AC adapter that generates predetermined DC power from AC power, and can also be used as a DC / DC converter with a power factor correction function.

  Further, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram showing a configuration of a switching power supply device according to an embodiment of the present invention. The figure for demonstrating the operation mode of the switching power supply device of FIG. The circuit diagram which shows the specific circuit structure of the switching power supply device of FIG. 4 is a timing chart showing the operation timing of the switching power supply device of FIG. 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... Rectifier circuit, 3 ... FET (2nd switch element), 4 ... Inductor, 5 ... FET (3rd switch element), 6 ... Diode, 7 ... Power factor improvement control circuit, 16 ... FET (first switch element), 100... Power factor correction circuit, 200... DC / DC converter, 300.

Claims (5)

A power factor correction circuit connected to the output terminal of the rectifier circuit that rectifies the input AC voltage;
A switching system that is connected to an output terminal of the power factor correction circuit via a smoothing capacitor and converts the input DC voltage to a predetermined DC voltage to be supplied to the load by switching control of the first switch element. A DC / DC converter;
A second switch element connected between an output terminal of the rectifier circuit and an output terminal of the power factor correction circuit so as to bypass the power factor correction circuit;
The output current of the DC / DC converter supplied to the load is detected, and when the output current is greater than or equal to a predetermined value, the second switch element is set to an off state, and the output current is less than the predetermined value. A switching power supply device comprising: a control circuit that sets the second switch element to an ON state when the number is small. The DC / DC converter is supplied from a transformer, an input circuit unit including the first switch element connected to the primary side of the transformer, and a smoothing circuit connected to the primary side of the transformer. A switching control circuit that is driven by a power supply voltage and controls the switching of the first switch element according to the value of the output voltage of the DC / DC converter; and an output smoothing circuit connected to the secondary side of the transformer; Including
The power factor correction circuit is driven by a power supply voltage supplied from a switching booster circuit including a third switch element and the smoothing circuit connected to a primary side of the transformer, and the third switch element Including a power factor correction control circuit for controlling switching,
A fourth switch element connected between the output terminal of the smoothing circuit and the power factor correction control circuit;
The control circuit sets the fourth switch element to an on state when the output current is greater than or equal to a predetermined value, and turns off the fourth switch element when the output current is less than a predetermined value. The switching power supply device according to claim 1, wherein   The control circuit includes a current detection resistor connected to an output of the output smoothing circuit, a detection circuit that detects a voltage across the current detection resistor, a voltage detected by the detection circuit, and a reference voltage A comparison circuit for comparing the second switch element and the fourth switch in response to an output signal from the comparison circuit, when the output current is equal to or greater than the predetermined value, A control signal having a first value for setting an element to an ON state is output, and when the output current is less than the predetermined value, the second switch element is set to an ON state and the fourth switch 3. The switching power supply device according to claim 2, further comprising a photocoupler that outputs a control signal having a second value for setting the switch element to an OFF state. A power factor correction circuit connected to the output terminal of the rectifier circuit for rectifying the input AC voltage; and a switching capacitor connected to the output terminal of the power factor correction circuit via a smoothing capacitor to control switching of the first switch element, A power supply control method for controlling a switching power supply device including a switching DC / DC converter that converts an input DC voltage into a predetermined DC voltage to be supplied to a load,
Detecting an output current of the DC / DC converter supplied to the load;
When the output current is greater than or equal to a predetermined value, the second switch element connected between the output terminal of the rectifier circuit and the output terminal of the power factor correction circuit is turned off so as to bypass the power factor correction circuit Step to set to
And a step of setting the second switch element to an ON state when the output current is less than a predetermined value. The DC / DC converter is supplied from a transformer, an input circuit unit including the first switch element connected to the primary side of the transformer, and a smoothing circuit connected to the primary side of the transformer. A switching control circuit that is driven by a power supply voltage and controls the switching of the first switch element according to the value of the output voltage of the DC / DC converter; and an output smoothing circuit connected to the secondary side of the transformer; Including
The power factor correction circuit is driven by a power supply voltage supplied from a switching booster circuit including a third switch element and the smoothing circuit connected to a primary side of the transformer, and the third switch element Including a power factor correction control circuit for controlling switching,
When the output current is equal to or greater than a predetermined value, setting a fourth switch element connected between the output terminal of the smoothing circuit and the power factor correction control circuit to an ON state;
5. The power supply control method according to claim 4, further comprising a step of setting the fourth switch element to an OFF state when the output current is less than a predetermined value.

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