JPH099626A - Switching regulator - Google Patents

Abstract

PURPOSE: To obtain a switching regulator in which the power loss, of an inrush- current preventing resistor, generated in the rise of a power-factor correction circuit is eliminated so as to prevent the resistor from being damaged. CONSTITUTION: In a switching regulator, an AC input is rectified, a capacitor is connected, via a power-factor correction circuit 31, from a parallel circuit by a resistor and by a switching element for bypass switching, both ends of the capacitor are used as inputs of a converter circuit, and electric power which is output from a second winding at a main transformer used for the converter circuit is controlled. In the switching regulator, the switching element for bypass switching is turned on at the same timing as the operating instruction of the power-factor correction circuit, and it is provided with an inrush-current preventing circuit system which short-circuits a resistor 3.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to switching regulators.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a first conventional example. The switching regulator shown in FIG. 2 has a resistor 211 that limits an inrush current to the input smoothing capacitor 204.
And a thyristor 212 connected in parallel to the resistor 211.
And a circuit for triggering the thyristor 212. (See, for example, Japanese Patent Application Laid-Open No. 1-107664) A drive pulse from the drive circuit 210 is applied to the base of the switching element 208 connected to the primary winding of the transformer 206, and the first secondary winding of the transformer 206 is provided. Generate an AC output to. The transformer 20 is used to supply power to the drive circuit 210 and to trigger the thyristor 212.
A second secondary winding is provided at 6, and the output of this winding constitutes the auxiliary power supply 209 together with the diode 209a and the capacitor 209b. If the drive state of the transformer 206 is not sufficient, power cannot be supplied to the drive circuit 210. Therefore, at the start-up stage of the device, the input voltage of the transformer 206 is supplied to the drive circuit 210 via the start-up circuit 205 composed of a resistor or the like. Supplied. The output of the auxiliary power supply 209 is input to the capacitor 217 via the resistor 216, and when the charging potential reaches a specified value, the thyristor 212 becomes conductive and the output of the bridge diode 203 is directly input to the input smoothing capacitor 204.

After the switch 202 is turned off, the next O
When the time until N is short, the capacitor that triggers the thyristor is insufficiently discharged, so that the thyristor conducts early and the problem that the inrush current becomes large is avoided. And a control circuit 225 for stopping or starting the operation of the drive circuit 210 is added for the same purpose. That is,
When the partial pressure of the resistors 221 and 222 is lower than a predetermined value, the diode 224 is turned on and the operation of the drive circuit 210 is stopped.

FIG. 3 is a circuit diagram showing a second conventional example.
The switching regulator shown in FIG. 3 includes a resistor 304 that limits an inrush current to the input smoothing capacitor 303, a thyristor 305 connected in parallel with the resistor 304, and a circuit for triggering the thyristor 305. . (For example, see Japanese Patent Laid-Open No. 5-56631) Bridge diode 302 and input smoothing capacitor 303
The DC voltage converted by the voltage dividing resistors 312, 31
It is divided by 3 and added to the gate capacitor 314. By changing the value of the gate capacitor 314, the rise time of the voltage applied to the gate of the thyristor 305 can be changed, so that the time for which the inrush current prevention circuit is released can be arbitrarily set.

[0005]

In this conventional switching regulator, the bypass closing / opening switching element has the power factor improving P after the AC power is turned on and the primary rush is completed.
The FC circuit operates and is triggered when the DC-DC converter starts up, causing a short circuit. Therefore, even after the completion of the primary rush, the power consumption of the power factor improving PFC circuit rises because it flows through the inrush current prevention resistor. , The loss of this resistor delays the rise of the power factor improving PFC circuit, and when this power loss is significant, the power factor improving PFC circuit does not operate, causing damage to this resistor or reducing reliability. There is a problem.

[0006]

In the switching regulator of the present invention, a capacitor is connected to an input power source from a parallel circuit of a resistor and a switching element for bypass closing and opening via a power factor improving PFC circuit, and both ends of this capacitor are connected. In the switching regulator for controlling the electric power output from the second winding of the main transformer used as the input of the converter circuit, the bypass closing / opening switching element serves as an operation instruction of the power factor improving PFC circuit. It is configured with an inrush current prevention circuit that turns on at the same timing and short-circuits the resistor.

[0007]

The present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of a switching regulator according to the present invention. A rectifying section including a rectifying stack 1, a choke coil 2, a switching element 5, a diode 6, and a power factor improving PFC circuit section including a capacitor 7, A starter circuit unit including a starter circuit 8 and a diode 9, a switching unit 11, a transformer 12, a converter unit including a transformer resetting diode 10, a diode 18, an auxiliary power supply unit including a capacitor 19, a resistor 3, and a thyristor 4 are connected in parallel. Inrush current prevention circuit 1
A secondary side, a DC output section including the output rectifying circuit 13, and a secondary side connected from the power factor correction PFC ON signal 61 to the photocoupler 16 via the resistor 14 and the photocoupler 17 via the resistor 15 To be done.

The thyristor 4 in the preceding stage is triggered by a circuit connected from the diode OR output of the starting circuit section and the auxiliary power source section through the transistor 20 to the resistor 21 to the gate of the thyristor 4. Transistor 2
The base of 0 is connected to the resistor 22 and the series circuit on the light receiving side of the photocoupler 16 and connected to the ground, and the light emitting side of the photocoupler 16 is connected to the anode side from the power factor correction PFC circuit ON signal 61 via the resistor 14 It is grounded from the cathode side to SG. Further, since the power factor correction PFC circuit ON signal belongs to the secondary side, it is necessary to insulate it by the photocouplers 16 and 17 and transmit it to the primary side.

In the switching regulator configured as described above, when AC power is applied to the terminals 51 and 52, power is supplied to the capacitor 7 through the inrush prevention resistor 3 and after the completion of the primary inrush. The power factor correction PFC circuit ON signal 61 causes the photocoupler 17 via the resistor 15.
Current flows to the diode side of the and emits light, and the photocoupler 17
Since the transistor side of this receives this and turns it on, the diode OR output of the starting circuit section and the auxiliary power supply section causes the resistor 23
The ON signal is input to the power factor correction PFC circuit control unit 31 via the power factor correction PFC circuit control unit 31, and the power factor correction PFC circuit control unit 31 starts driving the switching element 5 and the output of the power factor correction PFC circuit starts to rise. The rate improving PFC circuit ON signal 61 causes a current to flow through the resistor 14 to the diode side of the photocoupler 16 to emit light, and the transistor side of the photocoupler 16 which receives the light turns on, so that the base of the transistor 20 turns on the resistor 22. The transistor 20 is turned on by being grounded via the ground to serve as a power supply for the starter circuit, and the trigger voltage of the thyristor 4 is applied by the series circuit of the transistor 20 and the resistor 21, the thyristor 4 is turned on, and the inrush prevention resistor is short-circuited. .

[0011]

As described above, according to the present invention, a capacitor is connected to an input power source from a parallel circuit of a resistor and a switching element for bypass closing / opening via a power factor correction PFC circuit, and both ends of this capacitor are connected to a converter. In the AC-DC conversion switching regulator that controls the power output from the second winding of the main transformer used as the input of the circuit used in this converter circuit, the bypass closing / opening switching element is a power factor improving PFC circuit. Inrush current prevention circuit system that turns on at the same timing as the operation instruction and short-circuits the inrush resistor. Power factor improvement Prevents damage to the inrush resistor or reduction in reliability due to current consumption when the PFC circuit is on. There is an effect that the rising of the improved PFC circuit can be accelerated.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a first conventional example.

FIG. 3 is a circuit diagram showing a second conventional example.

[Explanation of symbols]

 1 Rectification Stack 2 Choke Coil 4 Thyristor 8 Starter Circuit 12 Transformer 13 Rectification Smoothing Circuit 31 Power Factor Improvement PFC Circuit Control Unit 32 DC Output Control Unit

Claims (1)

[Claims] 1. A power factor improving PFC that rectifies an AC input and uses a parallel circuit of a resistor and a bypass closing switching element.
In a switching regulator that connects a capacitor via a circuit, uses both ends of this capacitor as input to the converter circuit, and controls the power output from the second winding of the main transformer used in this converter circuit, A switching regulator characterized in that a switching element is provided with an inrush current prevention circuit that turns on at the same timing as an operation instruction of a power factor correction PFC circuit and short-circuits a resistor.