JP3159065B2 - Switching power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a switching power supply circuit.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a conventional switching power supply circuit. In FIG. 4, a switching power supply circuit 400
Comprises a transformer 21, a control IC 22, a transistor 23 as a switching element, a diode 24, a smoothing capacitor 25, a starting resistor 26, and a base resistor 28. The control IC 22 has a control terminal 22a, a power supply voltage input terminal 22b, drive voltage input terminals 22c and 22d, and a ground terminal GND. The transformer 21 includes a primary winding 21a, a secondary winding 21b, and a base winding 21c.

The collector of the transistor 23 is a transformer 2
1 is connected to the primary winding 21a, and the emitter is also connected to the ground. And the base is base resistance 2
8 through the control terminal 2 of the control IC 22
2a. Base winding 21 of transformer 21
c is a power supply voltage input terminal 22 b and a drive voltage input terminal 22 of the control IC 22 via a diode 24.
c. The drive voltage input terminal 22d of the control IC 22 is connected to the ground, and the power supply voltage input terminal 22b is connected to the ground via the smoothing capacitor 25. The power supply voltage input terminal 22b is connected to the primary winding 21a via the starting resistor 26. The secondary side of the transformer 21 is omitted because it is not directly related to the present invention.

Next, the operation of the circuit will be described. When the input voltage is supplied to the switching power supply circuit 400, the starting resistance 2
6, the power supply voltage input terminal 2 of the control IC 22
The power supply voltage and the drive voltage are supplied to 2b and the drive voltage input terminal 22c, and the switching operation starts.
When the switching operation starts, a voltage is induced in the base winding 21c of the transformer 21 and this voltage is applied to the diode 2
4 and a smoothing capacitor 25 to be supplied to the power supply voltage input terminal 22b and the drive voltage input terminal 22c of the control IC 22.
The control terminal 22a of the control IC 22
Is substantially the same as the voltage supplied to the drive voltage input terminal 22c. The starting resistor 26 has a high resistance value and can supply only a necessary current at the time of starting. However, when the power supply voltage and the driving voltage are supplied to the control IC 22 from the base winding 21c, the current capacity becomes sufficient. Thereafter, the switching operation is continuously performed.

Incidentally, the loss in a transistor as a switching element includes a loss when driving the transistor (hereinafter referred to as a drive loss) in addition to a conduction loss between a collector and an emitter and a switching loss. The drive loss is mainly a loss between the base and the emitter and a loss at the base resistance, and is substantially proportional to the voltage supplied from the control IC to the switching element. In general, the lower limit of the drive voltage of the switching element is lower than the lower limit of the power supply voltage of the control IC. Therefore, any drive voltage higher than necessary causes drive loss. For example,
Assuming that the voltage applied to the drive voltage input terminal of the control IC is V1, the lower limit of the drive voltage of the switching element is V2, and the current flowing from the control IC to the switching element is I, the power of P = (V1−V2) × I is wasted. Will be consumed. Since this occurs each time switching is performed, this effect cannot be ignored, especially when the switching frequency is high.

[0006] In the circuit of FIG.
The power supply voltage of 22 and the drive voltage become the same, and the voltage at the time of ON of the signal output from the control terminal 22a, that is, the voltage applied to the base of the transistor 23 becomes the same voltage as the power supply voltage. In addition, the power supply voltage is set to a value slightly higher than its lower limit in order to avoid a malfunction of the control IC 22 due to a change in input voltage or load.
Further, depending on conditions, the power supply voltage may further increase, causing a further increase in drive loss.

In order to solve this problem, a switching power supply circuit shown in FIG. 5 has been proposed in Japanese Patent Application Laid-Open No. 6-098541. In FIG. 5, the switching power supply circuit 5
At 00, a constant voltage circuit 27 is inserted between the diode 24 and the smoothing capacitor 25. Other circuit configurations are the same as those in FIG. 4, and the same portions as those in FIG.
The description of the circuit is omitted. The constant voltage circuit 27 also has a general circuit configuration, and a detailed description of the circuit configuration is omitted.

[0008] The constant voltage circuit 27 converts the voltage induced in the base winding 21 c of the transformer 21 into a control IC 22.
Is stabilized to the minimum value required for driving
C22 is supplied to the power supply voltage input terminal 22b and the drive voltage input terminal 22c. This can prevent an increase in drive loss due to a change in input voltage or load condition.

[0009]

In the above-described conventional switching power supply circuit, the drive voltage of the control IC becomes the same as the power supply voltage, and the drive voltage cannot be set to an optimum value. As a result, the drive voltage becomes unnecessarily high, and even in the circuit shown in FIG. 5, the effect of reducing drive loss is not sufficient.

An object of the present invention is to provide a switching power supply circuit that further reduces drive loss.

[0011]

In order to solve the above-mentioned problems, a switching power supply circuit according to the present invention comprises a primary winding,
A transformer having a secondary winding and a base winding, a switching element connected in series to the primary winding of the transformer,
A control IC for controlling the switching timing of the switching element, and the control IC via a rectifier circuit connected to a base winding of the transformer;
In a switching power supply circuit to which a power supply voltage of C is supplied, the control IC has a drive voltage input terminal in addition to a power supply voltage input terminal, and the drive voltage supplied to the drive voltage input terminal is referred to as the power supply voltage. Is set to another lower value.

Further, a switching power supply circuit of the present invention
The primary side of the transformer and the drive voltage input terminal of the control IC are connected by a starting resistor, and the drive voltage input terminal of the control IC and the power supply voltage input terminal are connected by a diode. The input terminal side is an anode.

Further, the switching power supply circuit of the present invention comprises:
A drive voltage of the control IC is supplied through a rectifier circuit connected to a base winding of the transformer and further stabilized by a constant voltage circuit.

Further, the switching power supply circuit of the present invention comprises:
A first base winding and a second base winding having a smaller number of turns than the first base winding are provided on the transformer, and a power supply voltage of the control IC is connected to the first base winding. Supplied from the circuit and the control I
The drive voltage of C is supplied from a rectifier circuit connected to the second base winding.

With this configuration, in the switching power supply circuit of the present invention, drive loss can be reduced and the efficiency of the switching power supply circuit can be improved. Further, by using a diode, it is possible to reduce the loss due to the starting resistance by reducing the necessary starting resistance to one.

[0016]

FIG. 1 shows an embodiment of a switching power supply circuit according to the present invention. 1, a switching power supply circuit 100 includes a transformer 1, a control IC 2, a transistor 3 as a switching element, and a diode 4.
And 5, a constant voltage circuit 6, smoothing capacitors 7 and 8,
It is composed of starting resistors 9 and 10, and a base resistor 13. The control IC 2 includes a control terminal 2a, a power supply voltage input terminal 2b, drive voltage input terminals 2c and 2d, and a ground terminal GND. The transformer 1 includes a primary winding 1a, a secondary winding 1b, and a base winding 1c.

The collector of the transistor 3 is connected to the primary winding 1a of the transformer 1, and the emitter is connected to the ground. The base is connected to the control terminal 2a of the control IC 2 via the base resistor 13. The base winding 1c of the transformer 1 is connected to the power supply voltage input terminal 2b of the control IC 2 via the diode 4.
And the power supply voltage input terminal 2b is connected to the smoothing capacitor 7
Connected to the ground via Transformer 1
Is connected to a drive voltage input terminal 2c of the control IC 2 via a diode 5 and a constant voltage circuit 6, and the drive voltage input terminal 2c is connected to a smoothing capacitor 8
Connected to the ground via The drive voltage input terminal 2d is connected to the ground. The primary winding 1a of the transformer 1 and the power supply voltage input terminal 2b and the drive voltage input terminal 2c of the control IC 2 are connected via start-up resistors 9 and 10, respectively.

Next, the operation of the circuit will be described. When an input voltage is supplied to the switching power supply circuit 100, the starting resistor 9
The power supply voltage and the drive voltage are supplied to the power supply voltage input terminal 2b and the drive voltage input terminal 2c of the control IC 2 through the steps 10 and 10, and the switching operation starts. When the switching operation starts, a voltage is induced in the base winding 1c.
The power supply voltage is supplied to the power supply voltage input terminal 2b of C2.
Further, a drive voltage is supplied to the drive voltage input terminal 2c of the control IC 2 through a rectification / constant voltage circuit composed of a diode 5, a constant voltage circuit 6, and a smoothing capacitor 8. The number of turns of the base winding 1c of the transformer 1 is set to a value required to supply the power supply voltage of the control IC 2, and the constant voltage circuit 6 is set to a condition capable of outputting the voltage required to supply the drive voltage of the control IC 2. Is set.

As a result, the power supply voltage and the drive voltage of the control IC 2 are set to optimal values, respectively, so that the drive voltage alone does not become unnecessarily high, and drive loss can be reduced. In particular, this effect becomes more remarkable as the switching frequency becomes higher.

FIG. 2 shows another embodiment of the switching power supply circuit of the present invention. 2, a switching power supply circuit 200 includes a primary winding 1a of a transformer 1 and a control I.
The drive voltage input terminal 2c of C2 is connected via the starting resistor 11, the drive voltage input terminal 2c and the power supply voltage input terminal 2b are connected via the diode 12, and the drive voltage input terminal 2c side becomes the anode of the diode 12. Connected. The circuit configuration is the same as that of the circuit of FIG. 1 except that a starting resistor 11 is connected in place of the starting resistors 9 and 10, and a diode 12 is newly connected, and the same parts as those in FIG. The description of the circuit is omitted.

Next, the operation of the circuit will be described. When an input voltage is supplied to the switching power supply circuit 200, the starting resistance 1
1, a drive voltage is applied to the control IC 2 and a power supply voltage is applied to the control IC 2 through the diode 12, and the switching operation starts. The operation after switching is started is the same as that of the circuit of FIG. However, after the start, the voltage of the power supply voltage input terminal 2b becomes higher than that of the drive voltage input terminal 2c, but the backflow is prevented by the diode 12.

As a result, similarly to the circuit of FIG. 1, drive loss can be reduced.

A small amount of current always flows through the starting resistor 11 during the operation of the switching power supply circuit 200, which causes a loss. However, by using the diode 12 together with the starting resistor 11, the power supply voltage input terminal 2b There is no need to provide a starting resistor between the transformer and the primary side of the transformer 1.
As a result, two start-up resistors required when the power supply voltage and the drive voltage are separated can be substituted by one, and the loss due to the start-up resistor can be halved.

FIG. 3 shows another embodiment of the switching power supply circuit of the present invention. In FIG. 3, the switching power supply circuit 300 has a tap mounted in the middle of the base winding 1d of the transformer 1 so that two outputs can be taken out. The first output terminal 1e of the base winding 1d is connected to the power supply voltage input terminal 2b of the control IC 2 via the diode 4. Further, the power supply voltage input terminal 2b of the control IC 2 and the ground are connected via a smoothing capacitor 7. A second output terminal 1f of the base winding 1d is taken out from a tap on the way and connected to a drive voltage input terminal 2c of the control IC 2 via a diode 5. Further, the drive voltage input terminal 2c and the ground are connected via a smoothing capacitor 8. The other circuit configuration is the same as that of the circuit of FIG. 2, and the same parts as those of FIG.

Next, the operation of the circuit will be described. When the input voltage is supplied to the switching power supply circuit 300 and the switching operation starts, a voltage is induced in the base winding 1d of the transformer 1. First output terminal 1e of base winding 1d
Is induced by the diode 4 and the smoothing capacitor 7
Is supplied as a power supply voltage to the power supply voltage input terminal 2b of the control IC 2 through the rectifier circuit composed of. The voltage induced at the second output terminal 1f of the base winding 1d is supplied as a drive voltage to the drive voltage input terminal 2c of the control IC 2 through a rectification / constant voltage circuit composed of a diode 5 and a smoothing capacitor 8. You.
The number of turns of the base winding corresponding to the first and first output terminals is set to an optimum value required for the power supply voltage and the drive voltage, respectively. As a result, the drive voltage is not unnecessarily increased as in the circuit of FIG. 2, and the drive loss can be reduced.

Although a winding having an intermediate tap is used as the base winding in the circuit of FIG. 3, a similar result can be obtained by using two base windings having different numbers of windings.

Although a transistor is used as the switching element in the circuit described in the above embodiment, another element such as an FET may be used instead of the transistor.

[0028]

According to the switching power supply circuit of the present invention, by setting the drive voltage of the control IC lower than the power supply voltage, the drive loss can be reduced and the efficiency of the switching power supply circuit can be improved.

Further, the starting resistance is reduced to 1 by using a diode.
With this configuration, it is possible to prevent an increase in loss at the starting resistor.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a switching power supply circuit according to another embodiment of the present invention.

FIG. 3 is a circuit diagram of a switching power supply circuit according to another embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional general switching power supply circuit.

FIG. 5 is a circuit diagram of a conventional switching power supply circuit that takes measures against drive loss.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transformer 1a ... Primary winding 1b ... Secondary winding 1c ... Base winding 2 ... Control IC 2a ... Control terminal 2b ... Power supply voltage input terminal 2c, 2d ... Drive voltage input terminal 3 ... Transistor 4, 5 ... Diode 6 Constant voltage circuit 7, 8 Smoothing capacitor 9, 10 Starting resistor 13 Base resistor 13 100 Switching power supply circuit

Claims (4)

(57) [Claims] 1. A transformer having a primary winding, a secondary winding, and a base winding, a switching element connected in series to the primary winding of the transformer, and a control for controlling switching timing of the switching element. A switching power supply circuit having an IC, wherein a power supply voltage is supplied to a power supply voltage input terminal of the control IC via a rectifier circuit connected to a base winding of the transformer, wherein the control IC is connected to a power supply voltage input terminal. In addition, a switching power supply circuit having a drive voltage input terminal, wherein a drive voltage supplied to the drive voltage input terminal is set to a value lower than the power supply voltage. 2. A primary side of the transformer and a drive voltage input terminal of the control IC are connected by a starting resistor, and the drive voltage input terminal of the control IC and the power supply voltage input terminal are connected by a diode. 2. The switching power supply circuit according to claim 1, wherein the diode has an anode on the drive voltage input terminal side. 3. The control voltage of the control IC is supplied via a rectifier circuit connected to a base winding of the transformer and further stabilized by a constant voltage circuit. 3. The switching power supply circuit according to item 1. 4. A transformer comprising: a first base winding;
A second base winding having a smaller number of turns than the first base winding is provided, a power supply voltage of the control IC is supplied from a rectifier circuit connected to the first base winding, and a drive of the control IC is provided. The switching power supply circuit according to claim 1, wherein the voltage is supplied from a rectifier circuit connected to the second base winding.