JP2005051942A - Switching power circuit and switching regulator equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To offer a switching power circuit which can control the power consumption in a starting resistor, relating to a switching power circuit which supplies a switching element with input voltage via a starting resistor. <P>SOLUTION: This switching power circuit is equipped with a transistor T which has auxiliary winding S in primary winding, a switching element F which is connected to the primary winding of the transistor T, a starting resistor R1, an auxiliary power circuit 4 which generates auxiliary power, based on the voltage induced in the auxiliary winding S, a transistor Q which is switched off by this auxiliary winding S when the auxiliary power is generated in the auxiliary power source 4, and a voltage supply resistor R2 which switches off the switching element F by supplying it with this auxiliary power when the auxiliary power is generated in the auxiliary power circuit 4. When the transistor Q is ON, DC power is supplied to the field effect transistor F, and when the transistor Q is off, the auxiliary power is supplied to the field effect transistor F. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a switching power supply circuit and a switching regulator including the same.

  Conventionally, in a switching power supply circuit using an RCC (Ringing Choke Converter) method in a switching regulator, an AC voltage from a commercial AC power supply is rectified and smoothed, and the DC voltage obtained thereby is switched by a switching element to increase the voltage. It is converted into an alternating voltage having a frequency. Then, a desired DC voltage is generated from this AC voltage using a high frequency transformer, and this DC voltage is used as an internal power supply voltage of an electronic device, for example.

  FIG. 3 is a circuit diagram showing an example of such a switching power supply circuit. In this switching power supply circuit, for example, a field effect transistor F is provided as a switching element, and a DC voltage from the input power supply circuit 11 is driven between the gate terminal of the field effect transistor F and the output terminal of the input power supply circuit 11 as a driving voltage. Is connected to the field effect transistor F. The resistor R11 supplies the DC voltage of the input power supply circuit 11 to the gate terminal of the field effect transistor F when the power switch (not shown) provided in the input power supply circuit 11 is turned on (closed). The effect transistor F is turned on, that is, the current is passed through the primary winding of the high-frequency transformer T to activate the switching power supply circuit. Hereinafter, this resistor R11 is referred to as a starting resistor R11.

  The output terminal of the input power supply circuit 11 is connected to the primary winding side of the high-frequency transformer T having the auxiliary winding S, and the drain terminal of the field effect transistor F is connected to the primary winding side of the high-frequency transformer T. Has been. The gate terminal of the field effect transistor F is provided with a drive circuit 12 for switching control of the field effect transistor F, and the drive circuit 12 is supplied with a power supply voltage from the auxiliary winding S of the high-frequency transformer T. It has become. A load (not shown) is connected to the secondary winding side of the high-frequency transformer T via a rectifying and smoothing circuit 13.

  With this configuration, when the power switch is turned on and a DC voltage (for example, DC 140 V) is applied from the input power supply circuit 11, the field effect transistor F is turned on by the starting resistor R11, and current is supplied to the primary winding side of the high-frequency transformer T. While flowing, a voltage is induced in the auxiliary winding S of the high-frequency transformer T, and this voltage is supplied to the drive circuit 12 as a power supply voltage. As a result, the switching power supply circuit is activated, and thereafter, the drive circuit 12 controls the field effect transistor F to be turned on and off. As a result, for the load connected to the secondary winding side of the high-frequency transformer T, A DC voltage subjected to switching control is supplied via the rectifying and smoothing circuit 13.

  In this case, the waveform of the current flowing through the starting resistor R11 becomes a waveform as shown in FIG. 4 according to the switching control for the field effect transistor F of the drive circuit 12. That is, the gate terminal of the field effect transistor F becomes “LOW” level in accordance with the fall of the ON / OFF control signal (pulse signal) output from the drive circuit 12, and the field effect transistor F is turned off. At this time, an inrush current flows through the starting resistor R11, and the current flowing through the starting resistor R11 decreases with time, and an inrush current flows again into the starting resistor R11 by the on / off control signal from the drive circuit 12, Thereafter, the field effect transistor F is subjected to switching control in this cycle.

  However, according to the switching power supply circuit having the above configuration, every time the field effect transistor F is turned on, a DC voltage is supplied to the field effect transistor F via the starting resistor R11. Therefore, as shown in FIG. There is a problem in that a current also flows through the resistor R11 and the power consumption in the starting resistor R11 is large.

  Here, when the power loss of the starting resistor R11 is obtained, if AC100V, for example, is input to the input power supply circuit 11, the DC voltage output after rectification and smoothing is, for example, DC140V. If the current required for starting the field effect transistor F is Iin, the power loss in the starting resistor R11 is approximately 140 × Iin.

  Further, if AC240V, for example, is input to the input power supply circuit 11, the DC voltage output after rectification and smoothing is, for example, DC336V. Therefore, the power loss in the starting resistor R11 is obtained by approximately 336 × Iin.

An example of a method for suppressing power consumption in the starting resistor is a method disclosed in Patent Document 1. In the power suppression method according to Patent Document 1, a power supply is provided that has a switching transistor that is connected to a primary winding of a transformer and that switches a DC power supply applied to the primary winding, and that controls on and off of the switching transistor. When the DC power is supplied to the control circuit via the starting resistor and the switch circuit, an auxiliary winding is provided in the primary winding of the transformer, and a voltage is induced in the auxiliary winding. The driving power is generated from the induced voltage and supplied to the power control circuit. When the power switch is turned on, power is supplied to the power supply control circuit via the starting resistor, and the power supply control circuit is started. As a result, a current flows in the primary winding of the transformer and a voltage is induced in the auxiliary winding. Then, the starting resistor is separated from the power supply control circuit by the switch circuit, and the power supply control circuit is driven by a driving power source based on the induced voltage of the auxiliary winding, and by flowing a current to the starting resistor only at the time of starting, The power consumption in the starting resistor is reduced.
JP 7-123709 A

  However, the control method described in the above publication can be applied to a separately-excited oscillation type switching regulator, but cannot be applied to a self-excited oscillation type switching regulator.

  The present invention has been conceived under the circumstances described above, and is a switching power supply circuit that supplies input voltage to a switching element via a starting resistor, and that can suppress power consumption in the starting resistor. An object is to provide a power supply circuit.

  In order to solve the above problems, the present invention takes the following technical means.

  According to the switching power supply circuit provided by the first aspect of the present invention, a transformer having an auxiliary winding in a main winding, a switching element connected to the main winding of the transformer, and an input to the main winding A first resistor that is provided between one end of the DC power source to be controlled and the control terminal of the switching element, and that supplies the DC power source to turn on the switching element, and a voltage induced in the auxiliary winding A drive control circuit that is driven to turn on and off the switching element at a predetermined period; an auxiliary power generation means that generates an auxiliary power lower than the DC power based on a voltage induced in the auxiliary winding; and A switch that is provided between the first resistor and the control terminal of the switching element and is turned off by the auxiliary power source when the auxiliary power source is generated by the auxiliary power source generating means. And when the auxiliary power is generated by the auxiliary power generating means, the auxiliary power is supplied to turn on the switching element. And when the switch means is on, the DC power is supplied to the control terminal of the switching element, and when the switch means is off, the auxiliary power is supplied to the control terminal of the switching element. It is characterized by being.

  According to this invention, when the switching power supply circuit is activated, a DC power supply is input to the main winding (primary winding), and this DC power supply is supplied to the control terminal of the switching element by the first resistor. Turn on. When the switching element is turned on, a current flows in the main winding of the transformer, a voltage is induced in the auxiliary winding, and the drive control circuit is activated. When the drive control circuit is activated, the switching element is turned off at a predetermined cycle, so that the power supplied to the main winding is interrupted at a predetermined cycle, thereby inducing a voltage at the secondary winding of the transformer. It will be. When a voltage is induced in the auxiliary winding, an auxiliary power supply is generated by the auxiliary power generation means, and the switch means is turned off by the auxiliary power supply, so that the power supply to the control terminal of the switching element by the first resistor is performed. Although it is blocked, the auxiliary power supply is supplied to the control terminal of the switching element by the second resistor instead, so that the power generation operation of the switching power supply circuit is continued. When the switching power supply circuit is activated, the circuit for supplying power to the control terminal of the switching element is switched from the circuit including the DC power supply and the first resistor to the circuit including the auxiliary power supply generating means and the second resistor. Power consumption for turning on the element can be reduced.

  According to a preferred embodiment, the auxiliary power generation means includes a capacitor that is charged based on a voltage induced in the auxiliary winding, and the switch means has a charging voltage of the capacitor equal to or higher than a predetermined threshold value. When turned off.

  According to another preferred embodiment, the switching element may be composed of a MOS type field effect transistor.

  According to the switching regulator provided by the second aspect of the present invention, the switching power supply circuit according to the first aspect of the present invention is provided.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

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

  FIG. 1 is a circuit diagram showing a switching power supply circuit according to an embodiment of the present invention.

  This switching power supply circuit is applied to a switching regulator capable of outputting a stable power supply voltage, and employs a so-called RCC method (self-excited oscillation type). This switching regulator is used, for example, as a power source for various household equipment such as a hot water supply device having at least one of a hot water supply function, a bath reheating function, and a hot water heating function.

  As shown in FIG. 1, the switching power supply circuit includes an input power supply circuit 1, a starting resistor R1 (corresponding to a “first resistor” recited in the claims), and a MOS field effect transistor as a switching element. F, drive circuit 2, switch circuit 3, high-frequency transformer T, auxiliary power supply circuit 4, voltage supply resistor R2 (corresponding to “second resistor” recited in claims), secondary side And a rectifying / smoothing circuit 5.

  The input power supply circuit 1 includes a rectifier diode and a smoothing capacitor (not shown), and rectifies and smoothes, for example, a commercial power supply (for example, AC 100 V) input to the switching power supply circuit. The input power supply circuit 1 outputs DC140V, for example.

  A primary winding of a high frequency transformer T and a field effect transistor F are connected to the input power supply circuit 1 in series. The high-frequency transformer T transforms a voltage (that is, step-up or step-down) and transmits electric energy input to the primary winding side to the secondary winding side. A voltage or current is output to a load (not shown). The high-frequency transformer T includes an auxiliary winding S on the primary side.

  The field effect transistor F is for switching (intermittent) the DC voltage from the input power supply circuit 1 applied to the primary winding by opening and closing the circuit on the primary winding side of the high-frequency transformer T. It is turned on / off by a control signal from the circuit 2. The gate terminal of the field effect transistor F is connected to the drive circuit 2, its drain terminal is connected to one end of the primary winding of the high-frequency transformer T, and its source terminal is connected to the ground.

  The input power supply circuit 1 is connected to a starting resistor R1. A power switch (not shown) of a switching power circuit is provided in the input power circuit 1, and when the power switch is turned on, the starting resistor R1 applies a DC voltage (for example, DC 140V) from the input power circuit 1 to the switch circuit 3. Is supplied to the field effect transistor F, and the field effect transistor F is turned on, that is, the primary winding circuit of the high-frequency transformer T is closed to pass a current through the primary winding, and the auxiliary winding. A voltage is induced in S, thereby starting the switching power supply circuit. As will be described later, the switch circuit 3 is in an ON state (a state in which the starting resistor R1 is connected to the gate terminal of the field effect transistor F) at the time of starting.

  A switch circuit 3 is connected to the starting resistor R1. The switch circuit 3 includes a PNP type switching transistor Q and resistors R4 and R5, and is for permitting or blocking the supply of a DC voltage supplied from the starting resistor R1 to the field effect transistor F. The detailed connection configuration will be described. One end of the starting resistor R1 is connected to the emitter terminal of the switching transistor Q, the collector terminal is connected to the gate terminal of the field effect transistor F, and one end is connected to the ground. The other end of the connected resistor R3 is connected. A resistor R4 is connected between the base terminal of the switching transistor Q and the ground, and a resistor R5 is connected between the base terminal and the output terminal of the auxiliary power supply circuit 4 (a cathode terminal of a diode D1 described later). ing.

  When the power switch is in the off state, there is no output from the auxiliary power circuit 4, and therefore the switching transistor Q is in the on state (the start resistor R1 and the gate terminal of the field effect transistor F are in the conductive state). When the power switch is turned on, a voltage for turning off the switching transistor Q is not output from the auxiliary power circuit 4 immediately after this, so that the switching transistor Q is kept on for a while and is input to the gate terminal of the field effect transistor F during this time. A voltage obtained by dividing the DC voltage from the power supply circuit 1 by the starting resistor R1 and the resistor R3 is supplied, whereby the circuit on the primary winding side of the high-frequency transformer T is closed, and a current flows through the primary winding. The switching power supply circuit starts up. After that, when the output voltage from the auxiliary power supply circuit 4 rises, the switching transistor Q is turned off, the starting resistor R1 is disconnected from the gate terminal of the field effect transistor F, and the electric field of the DC voltage from the input power supply circuit 1 is reached. Supply to the effect transistor F is blocked.

  The auxiliary power supply circuit 4 rectifies and smoothes the voltage induced in the auxiliary winding S into a DC voltage (for example, DC 10V to 20V), and includes a rectifier diode D1 and a smoothing capacitor C1. The detailed connection configuration will be described. One end of the auxiliary winding S of the high-frequency transformer T is connected to the ground, and the anode terminal of the rectifier diode D1 is connected to the other end. The cathode terminal of the rectifier diode D1 and the auxiliary winding S A smoothing capacitor C1 is connected in parallel with one end of the capacitor. The smoothing capacitor C1 is made of, for example, an electrolytic capacitor, and is connected in parallel so that the positive side terminal is connected to the cathode terminal. As described above, the cathode terminal of the rectifier diode D1 is connected to the base terminal of the switching transistor Q via the resistor R5.

  One end of the voltage supply resistor R2 is connected to the cathode terminal of the rectifier diode D1, and the other end of the voltage supply resistor R2 is connected to the gate terminal of the field effect transistor F. This voltage supply resistor R2 is for supplying a DC voltage, which is induced and rectified and smoothed in the auxiliary winding S, to the field effect transistor F.

  The smoothing capacitor C1 also has a function of charging a current based on the voltage induced in the auxiliary winding S. That is, the voltage induced in the auxiliary winding S is supplied to the switch circuit 3 while being charged by the smoothing capacitor C1, and is used for the off control of the switch circuit 3 as described above. That is, when the charging voltage at both ends of the smoothing capacitor C1 becomes higher than a predetermined threshold (a predetermined voltage for turning off the switching transistor Q), the switching transistor Q is switched from the on state to the off state. When the switching transistor Q is switched to the OFF state, supply of a DC voltage from the input power supply circuit 1 to the field effect transistor F is blocked via the starting resistor R1.

  A drive circuit 2 is connected to the auxiliary winding S. The drive circuit 2 controls the on / off operation of the field effect transistor F, and is driven by supplying a voltage induced in the auxiliary winding S.

  A secondary-side rectifying and smoothing circuit 5 is connected to the secondary winding side of the high-frequency transformer T. The secondary side rectifying / smoothing circuit 5 includes a rectifying diode D2 and a smoothing capacitor C2, and rectifies and smoothes an AC voltage induced on the secondary winding side of the high-frequency transformer T. The anode terminal of the rectifier diode D2 is connected to one end on the secondary winding side of the high-frequency transformer T, and the minus terminal of the smoothing capacitor C2 is connected to the other end on the secondary winding side of the high-frequency transformer T. At the same time, it is connected to the output terminal b. The plus terminal of the smoothing capacitor C2 is connected to the cathode terminal of the rectifier diode D2 and to the output terminal a. A DC voltage is output from the output terminals a and b.

  Next, the operation of the above circuit configuration will be described with reference to the timing chart shown in FIG.

  From input power supply circuit 1, for example, a commercial power supply (for example, AC 100V) is rectified and smoothed by a rectifier diode and a smoothing capacitor (not shown), and a DC voltage (for example, DC 140V) is input to this switching power supply circuit.

  When the power switch is turned on from the off state, the switching transistor Q is turned on. Therefore, the DC voltage from the input power supply circuit 1 can be supplied to the gate terminal of the field effect transistor F through the starting resistor R1. Now, in FIG. 2, when the power switch is turned on at timing T1, the DC voltage output from the input power supply circuit 1 is supplied to the series circuit of the starting resistor R1 and the resistor R3, and the starting resistor R1 is shown in FIG. Thus, a current necessary to turn on the field effect transistor F flows.

  Since the driving voltage is supplied to the gate terminal of the field effect transistor F via the starting resistor R1, the resistor R3, and the switching transistor Q, the field effect transistor F is turned on and becomes conductive, and the primary winding of the high-frequency transformer T Current flows due to the DC voltage from the input power supply circuit 1.

  When a current flows to the primary winding side of the high-frequency transformer T, a voltage is induced in the auxiliary winding S, and the smoothing capacitor C1 of the auxiliary power supply circuit 4 is charged by the induced voltage. As a result, as shown in the timing chart of FIG. 2, when the voltage across the smoothing capacitor C1 rises and exceeds a predetermined threshold value at timing T2 (see point A in FIG. 2), the level of the base terminal of the switching transistor Q becomes From “LOW” to “HIGH”, the switching transistor Q is turned off. Therefore, the DC voltage from the input power supply circuit 1 supplied to the field effect transistor F is blocked by the switching transistor Q, and no current flows through the starting resistor R1.

  When the voltage across the smoothing capacitor C1 exceeds a predetermined threshold value, the voltage induced and rectified and smoothed in the auxiliary winding S is supplied to the field effect transistor F via the voltage supply resistor R2, and the voltage supply resistor R2 Current begins to flow (see point B in FIG. 2).

  On the other hand, when a voltage is induced in the auxiliary winding S at the timing T1, the induced voltage is supplied to the drive circuit 2, whereby the drive circuit 2 is activated and starts switching control of the field effect transistor F. That is, the drive circuit 2 turns off the field effect transistor F by setting the gate terminal of the field effect transistor F to the “LOW” level at a predetermined period.

  Since the driving voltage is supplied to the field effect transistor F via the starting resistor R1, the resistor R3, and the switching transistor Q from the timing T1 to the timing T2, the current waveform of the starting resistor R1 is from the driving circuit 2 An inrush current flows every time the output ON / OFF control signal (pulse signal) falls (see point D in FIG. 2), but after the timing T2, the starting resistor R1 is disconnected from the field effect transistor F, and the electric field Since the drive voltage is supplied from the auxiliary power supply circuit 4 to the effect transistor F via the voltage supply resistor R2 and the resistor R3, the on / off control signal (from the drive circuit 2) is changed to the current waveform of the voltage supply resistor R2. An inrush current flows every time the pulse signal) falls (see point C in FIG. 2). The field effect transistor F is switched by the driving circuit 2 and performs switching control of the input voltage supplied to the primary winding of the high-frequency transformer T. In the high-frequency transformer T, the voltage is converted into a desired voltage by the primary winding and the secondary winding, and the converted voltage is given to the load via the secondary-side rectifying and smoothing circuit 5.

  In the conventional configuration, after the starting resistor R11 starts the field effect transistor F, the DC voltage from the input power supply circuit 11 is supplied via the starting resistor R11 even during switching control by the field effect transistor F. Therefore, the power loss in the starting resistor R11 was large.

  However, according to the present embodiment, after the starting resistor R1 starts the field effect transistor F, the switching transistor Q of the switch circuit 3 is turned off based on the voltage induced in the auxiliary winding S of the high-frequency transformer T. Therefore, the supply of the input voltage to the field effect transistor F is blocked. The voltage induced in the auxiliary winding S is supplied to the field effect transistor F after being rectified and smoothed via the voltage supply resistor R2.

  In other words, a circuit for supplying a drive voltage to the gate terminal of the field effect transistor F includes an auxiliary winding S, an auxiliary power supply circuit 4, a voltage supply resistor R2, and a resistor R3 from the circuit including the input power supply circuit 1, the starting resistor R1, and the resistor R3. Is switched to a circuit consisting of Therefore, as will be described below, the power consumed by the circuit for supplying the drive voltage to the gate terminal of the field effect transistor F after the switching power supply is activated can be reduced.

  Here, when the power loss of the voltage supply resistor R2 is obtained, the DC voltage rectified and smoothed by the auxiliary power supply circuit 4 is, for example, DC 20V, and if the current required for driving the field effect transistor F is Iin, The power loss in the voltage supply resistor R2 is obtained by approximately 20 × Iin. When this result is compared with the power loss of the starting resistor R11 obtained in the column of the problem to be solved by the invention, it can be seen that it has been reduced to about 1/7.

  In addition, when the voltage input to the input power supply circuit 1 is, for example, AC 240V, the DC voltage rectified and smoothed by the auxiliary power supply circuit 4 is, for example, DC 20V. Therefore, the power loss in the voltage supply resistor R2 is approximately 20 ×. Calculated by Iin. Also in this result, it can be seen that the power loss in the voltage supply resistor R2 is significantly reduced compared to the power loss in the starting resistor R11.

  Of course, the scope of the present invention is not limited to the embodiment described above. The switching power supply circuit to which the present invention is applied may be either a constant voltage output power supply or a constant current output power supply. Further, either the step-down method or the step-up method may be used. Further, either the PAM control method or the PWM control method may be used. In short, any type or type of switching power supply circuit that does not depart from the scope of the present invention can be applied.

  In the above embodiment, the field effect transistor F and other various switching elements employed in the circuit can be appropriately changed to a MOSFET, a bipolar transistor, or the like. In addition, other circuit components in the above embodiment can be appropriately changed in design.

  Further, as a modification of the above-described embodiment, instead of the switching transistor Q that switches the power supplied to the gate terminal of the field effect transistor F, the power may be switched using, for example, a relay. In other words, instead of the switching transistor Q, a relay contact switch (normally closed type) is interposed between the starting resistor R1 and the voltage supply resistor R2, and the resistor R4 and the resistor R5 are eliminated to smooth the coil side of the relay. Connect to both ends of the capacitor C1 in parallel. In this way, since the contact switch of the relay is always closed, the DC power is supplied to the gate terminal of the field effect transistor F, and a voltage higher than a predetermined value is applied to the coil side of the relay by the auxiliary power. The relay contact switch is opened, and auxiliary power is supplied to the gate terminal of the field effect transistor F.

  The switching power supply circuit according to the above embodiment can be used as a switching power supply for various electronic devices.

It is a circuit diagram which shows the switching power supply circuit concerning the Example of this invention. It is a figure which shows the timing chart of a switching power supply circuit. It is a circuit diagram which shows the conventional switching power supply circuit. It is a figure which shows the timing chart of the conventional switching power supply circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input power supply circuit 2 Drive circuit 3 Switch circuit 4 Auxiliary power supply circuit 5 Secondary side rectification smoothing circuit F Field effect transistor Q Switching transistor R1 Starting resistance R2 Voltage supply resistance S Auxiliary winding T High frequency transformer

Claims (4)

A transformer having an auxiliary winding in the main winding;
A switching element connected to the main winding of the transformer;
A first resistor that is provided between one end of a DC power source input to the main winding and a control terminal of the switching element, and supplies the DC power source to turn on the switching element;
A drive control circuit that is driven by a voltage induced in the auxiliary winding and that turns on and off the switching element at a predetermined period;
Auxiliary power generating means for generating an auxiliary power lower than the DC power based on the voltage induced in the auxiliary winding;
Switch means provided between the first resistor and the control terminal of the switching element, and when auxiliary power is generated by the auxiliary power generation means, switch means that is turned off by the auxiliary power;
Provided between the auxiliary power generating means and the control terminal of the switching element, and when the auxiliary power generating means generates the auxiliary power, the auxiliary power is supplied to turn on the switching element. With resistance,
When the switch means is on, the DC power is supplied to the control terminal of the switching element, and when the switch means is off, the auxiliary power is supplied to the control terminal of the switching element, Switching power supply circuit. The auxiliary power generation means includes a capacitor charged based on a voltage induced in the auxiliary winding,
The switching power supply circuit according to claim 1, wherein the switch means is turned off when a charging voltage of the capacitor becomes a predetermined threshold value or more.   The switching power supply circuit according to claim 1, wherein the switching element is configured by a MOS field effect transistor.   A switching regulator comprising the switching power supply circuit according to claim 1.

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