JP2010166729A - Switching power supply apparatus - Google Patents

Switching power supply apparatus Download PDF

Info

Publication number
JP2010166729A
JP2010166729A JP2009007874A JP2009007874A JP2010166729A JP 2010166729 A JP2010166729 A JP 2010166729A JP 2009007874 A JP2009007874 A JP 2009007874A JP 2009007874 A JP2009007874 A JP 2009007874A JP 2010166729 A JP2010166729 A JP 2010166729A
Authority
JP
Japan
Prior art keywords
voltage
synchronous rectification
circuit
power supply
output
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
JP2009007874A
Other languages
Japanese (ja)
Inventor
Naohisa Okamoto
直久 岡本
Original Assignee
Nichicon Corp
ニチコン株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nichicon Corp, ニチコン株式会社 filed Critical Nichicon Corp
Priority to JP2009007874A priority Critical patent/JP2010166729A/en
Publication of JP2010166729A publication Critical patent/JP2010166729A/en
Pending legal-status Critical Current

Links

Images

Abstract

A flyback switching power supply device capable of reducing power consumption when a load circuit is lightly loaded.
A switching power supply device 1 switches a DC voltage on a primary side of a transformer XFM and outputs a predetermined output voltage to a secondary side, and synchronously rectifies the output voltage on the secondary side. A synchronous rectification switching element Q1 that stably supplies the load circuit 4, a synchronous rectification control unit 3 that controls on / off of the synchronous rectification switching element Q1, and a load state detection means 5 that detects the load state of the load circuit 4 And synchronous rectification circuit control means 6 for controlling the operation of the synchronous rectification control unit 3 based on the output of the load state detection means 5. When the synchronous rectifier circuit control means 6 determines that the load state of the load circuit 4 is a light load, the synchronous rectifier circuit control means 6 stops the supply of the power supply voltage to the synchronous rectifier controller 3 and outputs the output voltage with a diode parasitic to the synchronous rectifier switching element Q1. Rectify.
[Selection] Figure 1

Description

  The present invention relates to a switching power supply device, and in particular, includes a synchronous rectification switching element that synchronously rectifies an output voltage output to a secondary side of a transformer, and a synchronous rectification control unit that controls on / off of the synchronous rectification switching element. The present invention relates to a provided flyback switching power supply.

  As a conventional switching power supply device, for example, as shown in FIG. 3, a DC voltage obtained by rectifying and smoothing an AC power supply voltage is switched on the primary side of the transformer, and a predetermined output voltage is applied to the secondary side of the transformer. There is known a flyback type switching power supply device that includes a switching circuit that outputs and a synchronous rectifier circuit that synchronously rectifies the output voltage output to the secondary side of the transformer and stably supplies the output voltage to the load circuit (for example, Non-patent document 1). Here, the synchronous rectification circuit includes a synchronous rectification switching element composed of a MOSFET that synchronously rectifies an output voltage output to the secondary side of the transformer, and a synchronous rectification control that controls on / off of the synchronous rectification switching element. It is comprised from IC (synchronous rectification control part).

Referring to FIG. 3, this switching power supply device 13 is connected to a pair of lines 10, 11 ((+) side line 10 and (-) side line 11) on the secondary side of switching circuit 2 and transformer XFM. Synchronous rectification control IC (made by International Rectifier Co., Ltd .: IR1167S) 3, three resistors Rdc, resistor RMOT, resistor Rg, synchronous rectification switching element (MOSFET) Q 1, and smoothing capacitor Co are provided. The load circuit 4 is connected to the output side of the switching power supply device 13.
The switching circuit 2 includes a Vin terminal and an Rtn terminal that receive a DC voltage obtained by rectifying and smoothing an AC voltage of an AC power supply (not shown), and a (−) side of the primary side winding N1 of the transformer XFM. And a switching element connected to the line 11 side. This switching element switches the DC voltage received at the Vin terminal and the Rtn terminal, and outputs a predetermined output voltage to the secondary side of the transformer XFM.
The synchronous rectification control IC 3 has a plurality of terminals, among which the VCC terminal, the OVT terminal, and the EN terminal are connected to the (+) side line 10 of the secondary winding N2 of the transformer XFM via a resistor Rdc. Connected. The VD terminal is connected to the drain of the synchronous rectification switching element Q1, the GND terminal and the VS terminal are connected to the source of the synchronous rectification switching element Q1, and the VGATE terminal is connected to the gate of the synchronous rectification switching element Q1 via the resistor Rg. ing. The smoothing capacitor Co is interposed between the source of the synchronous rectification switching element Q1 and the (+) side line 10.

Next, the operation of the switching power supply device 13 will be briefly described.
When the primary side switching element of the transformer XFM starts switching, a voltage is induced in the secondary winding N2 of the transformer XFM. The voltage induced in the secondary winding N2 is rectified by a diode parasitic between the drain and source of the synchronous rectification switching element Q1, smoothed by the smoothing capacitor Co, and converted into a DC output voltage. When the voltage across the smoothing capacitor Co rises to the starting voltage of the synchronous rectification control IC3, the synchronous rectification control IC3 operates in response to the supply of the output voltage.

  The voltage between the drain and source of the synchronous rectification switching element Q1 is detected at the VD terminal and the VS terminal of the synchronous rectification control IC3. Based on the detection result of the voltage, the synchronous rectification control IC 3 applies an on / off signal to the synchronous rectification switching element Q1 from the VGATE terminal to the gate of the synchronous rectification switching element Q1 via the resistor Rg. Performs synchronous rectification. According to the switching power supply device provided with such a synchronous rectification circuit (synchronous rectification switching element and synchronous rectification control IC), electric power is compared with the case where rectification is performed using a diode (eg, a Schottky barrier diode) as a discrete component. Loss can be greatly reduced.

Product Catalog "SmartRectifier CONTROL IC IR1167 ASPbF / IR1167BSPbF Data Sheet" Application Diagram (1 page), International Rectifier (Internet Rectifier), Internet, <http: //product-irinfo.sheet data / ir1167aspbf.pdf>

  However, since the synchronous rectification control IC 3 always operates regardless of the load state of the load circuit 4 of the switching power supply device 13, even if the load circuit 4 of the switching power supply device 13 is a light load, the synchronous rectification control is performed. The power accompanying the operation of the IC 3 is always consumed. In other words, by adopting a synchronous rectifier circuit, power loss can be greatly reduced in a normal load state compared to rectifying using a discrete component diode, while using a discrete component diode at light loads. Compared with the case of rectification, the power loss is rather increased.

  The present invention has been made in view of the above circumstances, and in a flyback type switching power supply device including a synchronous rectification switching element and a synchronous rectification control unit that controls on / off of the synchronous rectification switching element, Provided is a switching power supply device capable of reducing power consumption when a load circuit is lightly loaded.

In order to solve the above-mentioned problems, the present invention switches a DC voltage obtained by rectifying and smoothing an AC power supply voltage on the primary side of the transformer to output a predetermined output voltage on the secondary side of the transformer. A flyback switching power supply device comprising a circuit and a synchronous rectifier circuit connected to the secondary side of the transformer and synchronously rectifying the output voltage output to the secondary side of the transformer and stably supplying the output voltage to a load circuit And further comprising: a load state detection unit for detecting a load state of the load circuit; and a synchronous rectification circuit control unit for controlling an operation of the synchronous rectification circuit based on an output of the load state detection unit. The circuit includes a synchronous rectification switching element that synchronously rectifies the output voltage, and a synchronous rectification control unit that controls on / off of the synchronous rectification switching element. And the synchronous rectification circuit control means stops the supply of power supply voltage to the synchronous rectification control section when the load state of the load circuit detected by the load state detection means is determined to be a light load. Provided is a switching power supply characterized in that the output voltage is rectified by a diode parasitic on a rectifying switching element.
According to this configuration, when the load state of the load circuit detected by the load state detection unit is determined to be light, supply of the power supply voltage to the synchronous rectification control unit is stopped, and the synchronous rectification switching element is parasitically generated. The output voltage is rectified by the diode. For this reason, it is possible to avoid a state in which the synchronous rectification control unit always operates regardless of the load state of the load circuit, and it is possible to reduce power consumption at light load.
In the above configuration, when the power consumption associated with the operation of the synchronous rectification control unit is greater than the power loss associated with the rectification operation of the diode parasitic to the synchronous rectification switching element, It is preferable to determine that the state is a light load.

According to a first preferred embodiment of the present invention, the load state detection means comprises a current detection circuit for detecting an output current flowing in the load circuit, and the synchronous rectification circuit control means is detected by the current detection circuit. A comparison circuit that compares the detection signal level based on the output current and a preset reference signal level, and the supply / supply stop of the power supply voltage to the synchronous rectification control unit according to the comparison result of the comparison circuit It consists of a synchronous rectifier circuit control circuit to control.
According to this configuration, the load state detection unit includes the current detection circuit, and the synchronous rectification circuit control unit includes the comparison circuit and the synchronous rectification circuit control circuit. The current detection circuit detects the load state based on the output current flowing through the load circuit, and the comparison circuit compares the detection signal level based on the output current detected by the current detection circuit with a preset reference signal level. The synchronous rectification circuit control circuit controls the supply / supply stop of the power supply voltage to the synchronous rectification control unit according to the comparison result of the comparison circuit. For this reason, it is possible to avoid a state in which the synchronous rectification control unit always operates regardless of the load state of the load circuit, and it is possible to reduce power consumption at light load.

More preferably, in the first embodiment, the current detection circuit includes a resistor connected in series to the load circuit, and the comparison circuit includes a Zener diode and is generated in the resistor due to a current flowing through the resistor. (+) Input terminal to which voltage is input, (−) input terminal to which a reference voltage set using the Zener diode is input, and input to the (+) input terminal and the (−) input terminal, respectively When the (+) input terminal voltage is higher than the (−) input terminal voltage, an H level is output, while the (+) input terminal voltage becomes the (−) input terminal voltage. And an output terminal that outputs an L level when the output is low, and the synchronous rectification circuit control circuit includes one or more transistors interposed between the output terminal and the synchronous rectification control unit. A power supply voltage is supplied to the synchronous rectification control unit when the output from the output terminal is at an H level, and the load of the load circuit is output when the output from the output terminal is at an L level. The state is determined to be a light load, and the supply of the power supply voltage to the synchronous rectification control unit is stopped.
According to this configuration, the current detection circuit is configured by a resistor, the comparison circuit is configured by a Zener diode and an operational amplifier, and the synchronous rectification circuit control circuit is configured by one or more transistors. The resistance of the current detection circuit detects the load state, and the operational amplifier of the comparison circuit compares the voltage input to the (+) input terminal with the reference voltage input to the (−) input terminal, and compares this According to the output from the output terminal of the circuit, when the synchronous rectifier circuit control circuit determines that the output from the output terminal of the operational amplifier is at the H level, the power supply voltage is supplied to the synchronous rectification control unit, while the output terminal When the output from is determined to be L level, the supply of the power supply voltage to the synchronous rectification control unit is stopped. For this reason, it is possible to avoid a state in which the synchronous rectification control unit always operates regardless of the load state of the load circuit, and it is possible to reduce power consumption at light load.

According to a second preferred embodiment of the present invention, the load state detection means comprises a voltage detection circuit for detecting the output voltage, and the synchronous rectification circuit control means has an output detected by the voltage detection circuit. A comparison circuit that compares a detection signal level based on a voltage with a preset reference signal level, and controls supply / stop of supply of the power supply voltage to the synchronous rectification control unit according to a comparison result of the comparison circuit It consists of a synchronous rectifier circuit control circuit.
According to this configuration, the load state detection means is composed of a voltage detection circuit, and the synchronous rectification circuit control means is composed of a comparison circuit and a synchronous rectification circuit control circuit. The voltage detection circuit detects the load state based on the voltage supplied to the load circuit, and the comparison circuit compares the detection signal level based on the output voltage detected by the voltage detection circuit with a preset reference signal level. The synchronous rectification circuit control circuit controls the supply / supply stop of the supply of the power supply voltage to the synchronous rectification control unit according to the comparison result of the comparison circuit. For this reason, it is possible to avoid a state in which the synchronous rectification control unit always operates regardless of the load state of the load circuit, and it is possible to reduce power consumption at light load.

In the second embodiment, more preferably, the voltage detection circuit is connected in parallel between a diode, two resistors, and one of the two resistors connected in series between both sides of the secondary winding of the transformer. (+) Input terminal to which the voltage between the terminals of the capacitor generated by applying the output voltage to the capacitor is input, and the Zener The (−) input terminal to which a reference voltage set using a diode is input is compared with the voltages input to the (+) input terminal and the (−) input terminal, respectively, and the (+) input terminal voltage is compared. Output is H level when the voltage is higher than the (−) input terminal voltage, while L level is output when the (+) input terminal voltage is lower than the (−) input terminal voltage. And the synchronous rectification circuit control circuit has one or more transistors interposed between the output terminal and the synchronous rectification control unit, and outputs from the output terminal The power supply voltage is supplied to the synchronous rectification control unit when the signal is at the H level, while the load state of the load circuit is determined to be a light load when the output from the output terminal is at the L level. The supply of the power supply voltage to the control unit is stopped.
According to this configuration, the voltage detection circuit includes a diode, two resistors, and a capacitor, the comparison circuit includes a Zener diode and an operational amplifier, and the synchronous rectification circuit control circuit includes one or more transistors. The capacitor of the voltage detection circuit detects the load state, and the operational amplifier of the comparison circuit compares the voltage input to the (+) input terminal with the reference voltage input to the (−) input terminal, and compares this In response to the output from the output terminal of the circuit, the synchronous rectification circuit control circuit supplies the power supply voltage to the synchronous rectification control unit when the output from the output terminal of the operational amplifier is determined to be H level, When it is determined that the output from the terminal is at the L level, the supply of the power supply voltage to the synchronous rectification control unit is stopped. For this reason, it is possible to avoid a state in which the synchronous rectification control unit always operates regardless of the load state of the load circuit, and it is possible to reduce power consumption at light load.

  ADVANTAGE OF THE INVENTION According to this invention, when a load circuit is light load, the switching power supply device which can reduce power consumption 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 switching power supply device by 2nd Example of this invention. It is a circuit diagram of the conventional switching power supply device.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit diagram of a switching power supply apparatus according to a first embodiment of the present invention. Here, in order to clarify the correspondence with the conventional switching power supply apparatus described with reference to FIG. 3, the same reference numerals are given to the same constituent elements as those shown in FIG. Is omitted.

With reference to FIG. 1, this switching power supply device 1 includes a switching circuit 2 and a synchronous rectification control IC (synchronous rectification) on a pair of lines 10 and 11 ((+) side line 10 and (−) side line 11). Controller 3), three resistors Rdc, resistor RMOT, resistor Rg, synchronous rectification switching element (MOSFET) Q1, smoothing capacitor Co, load state detection means 5, and synchronous rectification circuit control means 6. The load circuit 4 is connected to the output side of the switching power supply device 1.
The load state detection means 5 includes a resistor R1 interposed on the (−) side line 11 of the switching power supply device 1 (between the load circuit 4 and the source of the synchronous rectification switching element Q1), and includes a current detection circuit. Configure.
The synchronous rectifier circuit control means 6 includes a comparison circuit 7 and a synchronous rectifier circuit control circuit 8.
The comparison circuit 7 includes a Zener diode ZD, resistors R2 and R3, and an operational amplifier 9. The anode of the Zener diode ZD is connected to the (−) line 11 on the secondary side of the transformer XFM, while the cathode is connected to the (+) line 10 on the secondary side of the transformer XFM via a resistor. The (+) input terminal 9a of the operational amplifier 9 is connected to the load circuit 4 side of the resistor R1, and the voltage generated in the resistor R1 due to the current flowing through the resistor R1 is input. The (−) input terminal 9b of the operational amplifier 9 is connected to the resistor R2 side of the resistor R3 (the connection point between the resistor R3 and the resistor R2), and is set by dividing the voltage of the Zener diode ZD by the resistors R2 and R3. A reference voltage is input. Here, the resistors R2 and R3 are connected in series, and the resistors R2 and R3 are connected in parallel with the Zener diode ZD so as to connect both terminals of the Zener diode ZD. The output terminal 9c of the operational amplifier 9 compares the voltages input to the (+) input terminal 9a and the (−) input terminal 9b, respectively, and the voltage at the (+) input terminal 9a is compared with the voltage at the (−) input terminal 9b. If the voltage is high, the H level is output. On the other hand, if the voltage at the (+) input terminal 9a is lower than the voltage at the (−) input terminal 9b, the L level is output.
The synchronous rectifier circuit control circuit 8 includes an NPN transistor Q2, a PNP transistor Q3, and resistors R4 and R5. The NPN transistor Q2 has a base connected to the output terminal 9c of the operational amplifier 9 via the resistor R4, and an emitter connected to the (−) side line 11. The PNP transistor Q3 has a base connected to the collector of the NPN transistor Q2 via the resistor R5, an emitter connected to the (+) side line 10, and a collector connected to the VCC terminal OVT of the synchronous rectification control IC3 via the resistor Rdc. It is connected to the terminal and EN terminal.

Next, the operation of the switching power supply device 1 of the first embodiment will be briefly described.
When the switching element on the primary side of the transformer XFM starts switching, an output voltage is induced in the secondary winding N2 of the transformer XFM. The output voltage induced in the secondary winding N2 is rectified by a diode parasitic between the drain and source of the synchronous rectification switching element Q1, smoothed by the smoothing capacitor Co, and converted into a DC output voltage. When the voltage across the smoothing capacitor Co rises to the starting voltage of the synchronous rectification control IC3, the synchronous rectification control IC3 operates in response to the supply of the output voltage.

  The voltage between the drain and source of the synchronous rectification switching element Q1 is detected at the VD terminal and the VS terminal of the synchronous rectification control IC3. Based on the detection result of the voltage, the synchronous rectification control IC 3 applies an on / off signal to the synchronous rectification switching element Q1 from the VGATE terminal to the gate of the synchronous rectification switching element Q1 via the resistor Rg. Performs synchronous rectification.

  In the switching power supply device 1, when the load state of the load circuit 4 becomes a light load (a state in which the output load is reduced or no load state), the current flowing through the resistor R1 decreases, the voltage generated in the resistor R1 decreases, and the operational amplifier 9 The voltage input to the (+) input terminal 9a decreases. The operational amplifier 9 compares the voltage input to the (+) input terminal 9a with the reference voltage preset by the Zener diode ZD, and the voltage input to the (+) input terminal 9a is higher than the reference voltage. When it becomes low, an L level voltage is output from the output terminal 9c. As a result, the NPN transistor Q2 is turned off, so that the PNP transistor Q3 is turned off. When the PNP transistor Q3 is turned off, supply of the power supply voltage to the VCC terminal, the OVT terminal, and the EN terminal of the synchronous rectification control IC3 is stopped, and the operation of the synchronous rectification control IC3 is stopped.

  In the switching power supply device 1, when the operation of the synchronous rectification control IC3 is stopped, the rectification operation of the synchronous rectification switching element Q1 by the on / off control of the synchronous rectification control IC3 is parasitic between the drain and the source of the synchronous rectification switching element Q1. Switch to diode rectification. Thereby, the power loss accompanying the continuous operation of the synchronous rectification control IC 3 can be reduced, and the power consumption can be reduced. That is, when the load is light, the rectification operation by the diode parasitic between the drain and the source of the synchronous rectification switching element Q1 is more than the synchronous rectification operation of the synchronous rectification switching element Q1 by the on / off control of the synchronous rectification control IC3. Power loss can be reduced. Therefore, as in the first embodiment, the synchronous rectification circuit control means 6 performs the synchronous rectification switching element Q1 from the synchronous rectification operation of the synchronous rectification switching element Q1 by the on / off control of the synchronous rectification control IC3 at the time of light load. By switching to a rectifying operation using a diode parasitic between the drain and source of the switching power supply, power consumption at light load can be reduced in the switching power supply device.

  In the switching power supply device 1, when the load state of the load circuit 4 becomes a normal load (in which the output load increases), the current flowing through the resistor R1 increases, the voltage generated in the resistor R1 increases, and the (+) of the operational amplifier 9 The voltage input to the input terminal 9a increases. The operational amplifier 9 compares the voltage input to the (+) input terminal 9a with the reference voltage preset by the Zener diode ZD, and the voltage input to the (+) input terminal 9a is higher than the reference voltage. When it becomes higher, an H level voltage is output from the output terminal 9c. As a result, the NPN transistor Q2 is turned on, so that the PNP transistor Q3 is turned on. When the PNP transistor Q3 is turned on, power supply voltage is supplied to the VCC terminal, OVT terminal and EN terminal of the synchronous rectification control IC, and the synchronous rectification control IC operates. As a result, the synchronous rectification operation of the synchronous rectification switching element Q1 by the on / off control of the synchronous rectification control IC 3 is started.

(Comparison of input power)
When a conventional circuit is used in a switching power supply of a flyback method at a switching frequency of 70 kHz, an input voltage of AC 100 V, an output condition of 16 V, and 0 A (switching power supply device 13 according to the conventional example shown in FIG. 3), and the present application circuit (FIG. Table 1 shows the results of comparative measurement of the input power in the case of using the switching power supply device 1) according to the first embodiment shown in FIG.

  As is apparent from Table 1, the switching power supply device 1 according to the first example was able to significantly reduce the input power as compared with the switching power supply device 13 according to the conventional example. This is because the synchronous rectification control IC always operates in the switching power supply device 13 according to the conventional example regardless of the load state of the load circuit. On the other hand, since the switching power supply device 1 according to the first embodiment stops the supply of the power supply voltage to the synchronous rectification control IC at light load (including no load), the synchronous rectification control IC It is possible to reduce power consumption associated with the operation.

(Second embodiment)
FIG. 2 is a circuit diagram of a switching power supply apparatus according to a second embodiment of the present invention. Here, in order to clarify the correspondence with the conventional switching power supply apparatus described with reference to FIG. 3, the same reference numerals are given to the same constituent elements as those shown in FIG. Is omitted.

Referring to FIG. 2, this switching power supply device 1 ′ includes a switching circuit 2, a synchronous rectification control IC (synchronous rectification control unit) 3, three resistors Rdc, a resistor RMOT, on a pair of lines 10 and 11. A resistor Rg, a synchronous rectification switching element (MOSFET) Q1, a smoothing capacitor Co, a load state detection means 5 ′, and a synchronous rectification circuit control means 6 ′ are provided, and a load is provided on the output side of the switching power supply 1 ′. A circuit 4 is connected.
The load state detection means 5 ′ includes a diode D and two resistors R6 and R7 connected in series between the (+) side line 10 and the (−) side line 11 on both sides of the secondary winding of the transformer XFM. An integration capacitor C connected in parallel to one of the two resistors R7 constitutes a voltage detection circuit.
The synchronous rectifier circuit control means 6 ′ is composed of a comparison circuit 7 ′ and a synchronous rectifier circuit control circuit 8 ′.
The comparison circuit 7 ′ includes a Zener diode ZD ′ and an operational amplifier 9 ′. The anode of the Zener diode ZD ′ is connected to the (−) line 11 on the secondary side of the transformer XFM, while the cathode is connected to the (+) line 10 on the secondary side of the transformer XFM via a resistor. The (+) input terminal 9a ′ of the operational amplifier 9 ′ is connected to the connection point of the resistors R6 and R7, and the output voltage supplied to the load circuit 4 is applied to the integrating capacitor C, whereby the integrating capacitor C is connected. The voltage generated between the terminals is input to the (+) input terminal 9a ′. The (−) input terminal 9b ′ of the operational amplifier 9 ′ is connected to the cathode of the Zener diode ZD ′ so that the reference voltage set by the voltage across the Zener diode ZD ′ is input to the (−) input terminal 9b ′. It has become. The output terminal 9c ′ of the operational amplifier 9 ′ compares the voltages input to the (+) input terminal 9a ′ and the (−) input terminal 9b ′, respectively, and the voltage at the (+) input terminal 9a ′ becomes the (−) input terminal. When the voltage is higher than the voltage 9b ', the H level is output. On the other hand, when the voltage at the (+) input terminal 9a' is lower than the voltage at the (-) input terminal 9b ', the L level is output.
The synchronous rectifier circuit control circuit 8 ′ includes an NPN transistor Q2 ′, a PNP transistor Q3 ′, and resistors R4 ′ and R5 ′. The NPN transistor Q4 ′ has a base connected to the output terminal 9c ′ of the operational amplifier 9 ′ via the resistor R4 ′, and an emitter connected to the (−) side line 11. The PNP transistor Q3 ′ has a base connected to the collector of the NPN transistor Q2 ′ via a resistor R5 ′, an emitter connected to the (+) side line 10, and a collector connected to the VCC of the synchronous rectification control IC3 via a resistor Rdc. The terminal, the OVT terminal, and the EN terminal are connected.

Next, the operation of the switching power supply device 1 ′ of the second embodiment will be briefly described.
When the switching element on the primary side of the transformer XFM starts switching, an output voltage is induced in the secondary winding N2 of the transformer XFM. The output voltage induced in the secondary winding N2 is rectified by a diode parasitic between the drain and source of the synchronous rectification switching element Q1, smoothed by the smoothing capacitor Co, and converted into a DC output voltage. When the voltage across the smoothing capacitor Co rises to the starting voltage of the synchronous rectification control IC3, the synchronous rectification control IC operates upon receiving this output voltage.

  The voltage between the drain and source of the synchronous rectification switching element Q1 is detected at the VD terminal and the VS terminal of the synchronous rectification control IC3. Based on the detection result of the voltage, the synchronous rectification control IC 3 applies an on / off signal to the synchronous rectification switching element Q1 from the VGATE terminal to the gate of the synchronous rectification switching element Q1 via the resistor Rg. Performs synchronous rectification.

  In the switching power supply device 1 ′, when the load state of the load circuit 4 becomes a light load (a state in which the output load is reduced or a no-load state), the off-time duty of the switching element on the primary side increases, so that the diode D rectifies Thereafter, the voltage of the integrating capacitor C obtained by integrating with the resistor R6 and the integrating capacitor C decreases, and the voltage input to the (+) input terminal 9a ′ of the operational amplifier 9 ′ decreases. Then, the operational amplifier 9 ′ compares the voltage input to the (+) input terminal 9a ′ with the reference voltage preset by the Zener diode ZD ′, and inputs the voltage to the (+) input terminal 9a ′ rather than the reference voltage. When the applied voltage becomes low, an L level voltage is output from the output terminal 9c ′ of the operational amplifier 9 ′. As a result, the NPN transistor Q2 'is turned off, so that the PNP transistor Q3' is turned off. When the PNP transistor Q3 'is turned off, supply of the power supply voltage to the VCC terminal, the OVT terminal, and the EN terminal of the synchronous rectification control IC3 is stopped, and the operation of the synchronous rectification control IC3 is stopped.

  When the operation of the synchronous rectification control IC 3 is stopped, the switching power supply device 1 ′ causes the rectification operation of the synchronous rectification switching element Q1 by the on / off control of the synchronous rectification control IC 3 to be parasitic between the drain and the source of the synchronous rectification switching element Q1. Switches to a rectifying operation using a diode. Thereby, similarly to the first embodiment, it is possible to reduce the power loss due to the continuous operation of the synchronous rectification control IC 3 and to reduce the power consumption.

  In the switching power supply device 1 ′, when the load state of the load circuit 4 becomes a normal load (in which the output load is increased), the off-time duty of the primary-side switching element becomes small. The voltage of the integrating capacitor C obtained by integrating with the integrating capacitor C increases, and the voltage input to the (+) input terminal 9a ′ of the operational amplifier 9 ′ increases. Then, the operational amplifier 9 ′ compares the voltage input to the (+) input terminal 9a ′ with the reference voltage preset by the Zener diode ZD ′, and inputs the voltage to the (+) input terminal 9a ′ rather than the reference voltage. When the applied voltage increases, an H level voltage is output from the output terminal 9c ′. As a result, the NPN transistor Q2 'is turned on, so that the PNP transistor Q3' is turned on. When the PNP transistor Q3 'is turned on, the power supply output voltage is supplied to the VCC terminal, the OVT terminal, and the EN terminal of the synchronous rectification control IC3, and the synchronous rectification control IC3 operates. As a result, the synchronous rectification operation of the synchronous rectification switching element Q1 by the on / off control of the synchronous rectification control IC 3 is started.

(Comparison of input power)
When a conventional circuit is used in a switching power supply of a flyback method at a switching frequency of 70 kHz, an input voltage of AC 100 V, an output condition of 16 V, and 0 A (switching power supply device 13 according to the conventional example shown in FIG. 3), and the present application circuit (FIG. Table 2 shows the results of measuring the input power in comparison with the case where the switching power supply device 1 ′) according to the second embodiment shown in FIG. 2 is used.

As is apparent from Table 2, the switching power supply 1 ′ according to the second example was able to significantly reduce the input power compared to the switching power supply 13 according to the conventional example.
According to the second embodiment, since the voltage generated in the transformer XFM is used, the power loss due to the detection resistor R1 as in the first embodiment (FIG. 1) does not occur. Therefore, even if the output current becomes a large current, the power loss due to the detection resistor does not increase.
On the other hand, according to the first embodiment, the load state can be stably detected regardless of the change in the input voltage on the primary side of the transformer XFM. That is, when the load state is detected using the voltage generated in the transformer, when the input voltage on the transformer primary side changes, the voltage generated on the transformer secondary side also changes (on the transformer primary side). When the input voltage increases, the load detection point also increases.) In the first embodiment, such a change in the load detection point can be avoided.
(Other)
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the load state detection method of the load circuit 4 is arbitrary, and the synchronous rectification circuit control unit is configured to perform power loss associated with the rectification operation of the diode parasitic on the synchronous rectification switching element Q1 based on the output of the load state detection unit. If the load state of the load circuit 4 is determined to be a light load when the power consumption associated with the operation of the synchronous rectification control IC 3 is larger than that, the effect of the present invention can be achieved.
In the above embodiment, the International Rectifier Co., Ltd .: IR1167S is used as the synchronous rectification control IC. However, the present invention is not limited to this, and the same type of synchronous rectification that performs on / off control of the synchronous rectification switching element is used. The present invention can be applied to a switching power supply device using a control circuit.

DESCRIPTION OF SYMBOLS 1 Switching power supply device 1 'Switching power supply device 2 Switching circuit 3 Synchronous rectification control IC (synchronous rectification control part)
4 Load circuit 5 Load state detection means 5 ′ Load state detection means 6 Synchronous rectification circuit control means 6 ′ Synchronous rectification circuit control means 7 Comparison circuit 7 ′ Comparison circuit 8 Synchronous rectification circuit control circuit 8 ′ Synchronous rectification circuit control circuit 9 Operational amplifier 9 'Operational amplifier 9a (+) input terminal 9a' (+) input terminal 9b (-) input terminal 9b '(-) input terminal 9c output terminal 9c' output terminal 10 (+) side line 11 (-) side line 13 Switching power supply Device C Integration Capacitor Co Smoothing Capacitor D Diode N1 Primary Side Winding N2 Secondary Side Winding Q1 Synchronous Rectification Switching Element (MOSFET)
Q2 NPN transistor Q2 'NPN transistor Q3 PNP transistor Q3' PNP transistor R1 Resistance (current detection circuit)
R2 Resistor R3 Resistor R4 Resistor R4 ′ Resistor R5 Resistor R5 ′ Resistor R6 Resistor R7 Resistor Rdc Resistor Rg Resistor RMOT Resistor XFM Transformer ZD Zener Diode ZD ′ Zener Diode

Claims (6)

  1. A switching circuit that switches the DC voltage obtained by rectifying and smoothing the AC power supply voltage on the primary side of the transformer and outputs a predetermined output voltage to the secondary side of the transformer, and is connected to the secondary side of the transformer In the flyback type switching power supply device comprising a synchronous rectification circuit that synchronously rectifies the output voltage output to the secondary side of the transformer and stably supplies it to a load circuit,
    A load state detecting unit for detecting a load state of the load circuit; and a synchronous rectification circuit control unit for controlling an operation of the synchronous rectifier circuit based on an output of the load state detecting unit;
    The synchronous rectification circuit includes a synchronous rectification switching element that synchronously rectifies the output voltage, and a synchronous rectification control unit that controls on / off of the synchronous rectification switching element,
    When the load state of the load circuit detected by the load state detection unit is determined to be a light load, the synchronous rectification circuit control unit stops supply of power supply voltage to the synchronous rectification control unit, and the synchronous rectification circuit control unit A switching power supply device, wherein the output voltage is rectified by a diode parasitic on the switching element.
  2.   The synchronous rectification circuit control means reduces the load state of the load circuit when the power consumption associated with the operation of the synchronous rectification control unit is greater than the power loss associated with the rectification operation of the diode parasitic to the synchronous rectification switching element. The switching power supply according to claim 1, wherein the switching power supply is determined as a load.
  3. The load state detection means comprises a current detection circuit for detecting an output current flowing in the load circuit;
    The synchronous rectifier circuit control means compares a detection signal level based on the output current detected by the current detection circuit with a preset reference signal level, and according to a comparison result of the comparison circuit, The switching power supply device according to claim 1, further comprising a synchronous rectification circuit control circuit that controls supply / stop of supply of the power supply voltage to the synchronous rectification control unit.
  4. The current detection circuit is composed of a resistor connected in series to the load circuit,
    The comparison circuit includes a Zener diode, and a (+) input terminal to which a voltage generated in the resistor due to a current flowing in the resistor is input, and a reference voltage set using the Zener diode is input ( When the voltage input to the (−) input terminal and the (+) input terminal and the (−) input terminal are compared, and the (+) input terminal voltage is higher than the (−) input terminal voltage, H An output terminal that outputs an L level when the (+) input terminal voltage is lower than the (−) input terminal voltage.
    The synchronous rectification circuit control circuit includes one or more transistors interposed between the output terminal and the synchronous rectification control unit, and the synchronous rectification control is performed when an output from the output terminal is at an H level. The power supply voltage is supplied to the unit, and when the output from the output terminal is at the L level, the load state of the load circuit is determined to be a light load and the power supply voltage is supplied to the synchronous rectification control unit. The switching power supply device according to claim 3, wherein the switching power supply device is stopped.
  5. The load state detection means comprises a voltage detection circuit for detecting the output voltage;
    The synchronous rectifier circuit control means compares the detection signal level based on the output voltage detected by the voltage detection circuit with a preset reference signal level, and according to the comparison result of the comparison circuit, The switching power supply device according to claim 1, further comprising a synchronous rectification circuit control circuit that controls supply / stop of supply of the power supply voltage to the synchronous rectification control unit.
  6. The voltage detection circuit is composed of a diode, two resistors, and a capacitor connected in parallel to one of the two resistors, connected in series between both sides of the secondary winding of the transformer,
    The comparison circuit has a Zener diode, and is set using a (+) input terminal to which a voltage between terminals of the capacitor generated by applying the output voltage to the capacitor is input, and the Zener diode. The (−) input terminal to which the reference voltage is input is compared with the voltages input to the (+) input terminal and the (−) input terminal, respectively, and the (+) input terminal voltage is compared with the (−) input. When the voltage is higher than the terminal voltage, an H level is output, while when the (+) input terminal voltage is lower than the (−) input terminal voltage, the output terminal outputs an L level.
    The synchronous rectification circuit control circuit includes one or more transistors interposed between the output terminal and the synchronous rectification control unit, and the synchronous rectification control is performed when an output from the output terminal is at an H level. The power supply voltage is supplied to the unit, and when the output from the output terminal is at the L level, the load state of the load circuit is determined to be a light load and the power supply voltage is supplied to the synchronous rectification control unit. The switching power supply device according to claim 5, wherein the switching power supply device is stopped.
JP2009007874A 2009-01-16 2009-01-16 Switching power supply apparatus Pending JP2010166729A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2009007874A JP2010166729A (en) 2009-01-16 2009-01-16 Switching power supply apparatus

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2009007874A JP2010166729A (en) 2009-01-16 2009-01-16 Switching power supply apparatus

Publications (1)

Publication Number Publication Date
JP2010166729A true JP2010166729A (en) 2010-07-29

Family

ID=42582451

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2009007874A Pending JP2010166729A (en) 2009-01-16 2009-01-16 Switching power supply apparatus

Country Status (1)

Country Link
JP (1) JP2010166729A (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012210122A (en) * 2011-03-30 2012-10-25 Yamaha Corp Rectifier circuit
JP2013175042A (en) * 2012-02-24 2013-09-05 Nissan Motor Co Ltd Current detector
CN105429487A (en) * 2014-09-12 2016-03-23 恩智浦有限公司 A controller for a switched mode power supply and associated methods
JP2016116413A (en) * 2014-12-17 2016-06-23 ローム株式会社 Insulation synchronous rectification type dc-dc converter, synchronous rectification controller, power supply unit having the same, power supply adapter and electronic apparatus, and control method for synchronous rectification transistor
JP2016158387A (en) * 2015-02-24 2016-09-01 ローム株式会社 Insulation synchronous rectification type dc/dc converter, synchronous rectification controller, power supply device employing the same, power supply adapter and electronic apparatus
US10408191B2 (en) 2016-03-21 2019-09-10 General Electric Company Wind pitch adjustment system

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000023456A (en) * 1998-07-06 2000-01-21 Sanken Electric Co Ltd Synchronized rectification dc/dc converter
JP2001224173A (en) * 1999-11-30 2001-08-17 Fuji Xerox Co Ltd Synchronous rectifying circuit and power supply
JP2004514390A (en) * 2000-11-11 2004-05-13 ミネベア株式会社 Power converter
JP2004282847A (en) * 2003-03-13 2004-10-07 Tdk Corp Switching power unit

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000023456A (en) * 1998-07-06 2000-01-21 Sanken Electric Co Ltd Synchronized rectification dc/dc converter
JP2001224173A (en) * 1999-11-30 2001-08-17 Fuji Xerox Co Ltd Synchronous rectifying circuit and power supply
JP2004514390A (en) * 2000-11-11 2004-05-13 ミネベア株式会社 Power converter
JP2004282847A (en) * 2003-03-13 2004-10-07 Tdk Corp Switching power unit

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012210122A (en) * 2011-03-30 2012-10-25 Yamaha Corp Rectifier circuit
JP2013175042A (en) * 2012-02-24 2013-09-05 Nissan Motor Co Ltd Current detector
CN105429487A (en) * 2014-09-12 2016-03-23 恩智浦有限公司 A controller for a switched mode power supply and associated methods
US10003210B2 (en) 2014-09-12 2018-06-19 Nxp B.V. Controller for a switched mode power supply and associated methods
CN105429487B (en) * 2014-09-12 2018-10-16 恩智浦有限公司 The controller and correlation technique of switched-mode power supply
JP2016116413A (en) * 2014-12-17 2016-06-23 ローム株式会社 Insulation synchronous rectification type dc-dc converter, synchronous rectification controller, power supply unit having the same, power supply adapter and electronic apparatus, and control method for synchronous rectification transistor
JP2016158387A (en) * 2015-02-24 2016-09-01 ローム株式会社 Insulation synchronous rectification type dc/dc converter, synchronous rectification controller, power supply device employing the same, power supply adapter and electronic apparatus
US10408191B2 (en) 2016-03-21 2019-09-10 General Electric Company Wind pitch adjustment system

Similar Documents

Publication Publication Date Title
EP1239577B1 (en) Power Supply Control Apparatus and Method thereof
US7339359B2 (en) Terminal for multiple functions in a power supply
JP5494009B2 (en) Switching control circuit and switching power supply device
JP4748197B2 (en) Power supply
US6690586B2 (en) Switching power source device
JP2017536076A5 (en)
KR100217699B1 (en) Power supply
US8953341B2 (en) Converter with reduced power consumption
US8964430B2 (en) Active snubber circuit and power supply circuit
JP4637694B2 (en) Power factor correction circuit and output voltage control method thereof
US20020089860A1 (en) Power supply circuit
JP6433652B2 (en) Power supply device and electrical equipment
US9722498B2 (en) Control circuit for switching power converters with synchronous rectifiers
US7835163B2 (en) Switching power converter with a secondary-side control
KR101468719B1 (en) Power converter and driving method thereof
JP2009201342A (en) Power-supply circuit of ac/dc converter
US6532159B2 (en) Switching power supply unit
KR100558453B1 (en) Flyback converter with synchronous rectifying function
US20070070658A1 (en) Energy effective switching power supply apparatus and an energy effective method thereof
KR20060044625A (en) Voltage detection circuit, power supply unit and semiconductor device
JP2005518177A (en) Power converter noise reduction
US7259973B2 (en) Semiconductor apparatus for controlling a switching power supply
JP6070164B2 (en) Switching power supply
JP4040056B2 (en) Output voltage detection circuit, isolated switching power supply, and semiconductor device
JP3733440B2 (en) Switching power supply

Legal Events

Date Code Title Description
A621 Written request for application examination

Effective date: 20110819

Free format text: JAPANESE INTERMEDIATE CODE: A621

A977 Report on retrieval

Effective date: 20121207

Free format text: JAPANESE INTERMEDIATE CODE: A971007

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20121212

A02 Decision of refusal

Free format text: JAPANESE INTERMEDIATE CODE: A02

Effective date: 20130410