JPH05176541A - Auxiliary power circuit - Google Patents

Abstract

PURPOSE:To enable direct and highly efficient acquisition of a DC auxiliary power source of low voltage and low current from a commercial AC power source by providing a switch circuit which monitors an instantaneous value of a pulsating voltage between a rectifying circuit and a smoothing capacitor connected to the output side of the rectifying circuit and executes operations for making and breaking according to whether the value is a set voltage or below. CONSTITUTION:An inputted AC voltage is converted into a pulsating voltage V1 by a bridge rectifying circuit l and it is supplied to a detecting circuit 2 and a switch circuit 3. When the output pulsating voltage V1 of the rectifying circuit 1 is a Zener voltage VZD1 or below, a transistor Q1 is broken, the potential of a node of a resistor R and a collector of the transistor Q1, i.e., a node of the detecting circuit 2 and the switch circuit 3, turns to be of a high level and a driving current is supplied to the switch circuit 3. In other words, the switch circuit 3 so operates as to lead the pulsating voltage V1 to an output only when this voltage is lower than the Zener voltage VZD1, according to a signal from the detecting circuit 2. That voltage is converted into a DC one by a smoothing capacitor C1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit, and more particularly to 1.
The auxiliary power supply circuit of the next circuit.

[0002]

2. Description of the Related Art A primary circuit of a switching regulator which requires an auxiliary power supply (low voltage, low current) is
Although there are a control circuit and a thyrist target drive circuit for a rush current prevention circuit, the auxiliary power supply for a control circuit will be described with reference to FIG. In a switching power supply circuit including an oscillation circuit and a control circuit in the primary circuit, in order to drive the original main switching power supply circuit, the control circuit including the oscillation circuit and the like must be operated and maintained first. I won't. Circuits therefor are the starting circuit 6 and the auxiliary power supply circuit 7. The starting circuit is a starting resistor R31, and the auxiliary power supply circuit is an auxiliary winding P2, a rectifying diode D1, and a capacitor C.
32, and is connected to the power supply line of the control circuit. Next, the operation will be described. When the AC switch SW1 is turned on, a DC voltage is generated across the smoothing capacitor C31. The starting current flows through the starting resistor R31,
C32 is charged and the power supply voltage (Vcc) of the control circuit gradually rises. When the power supply voltage (Vcc) reaches the activation start voltage of the control circuit, the control circuit starts oscillation and starts switching operation. At the same time, the current consumption of the control circuit increases and the power supply voltage begins to drop. Further, the rectified voltage of the winding P2 also starts to rise and reaches the rectified voltage of the winding P2 before the power supply voltage reaches the start-stop voltage, so that the switching operation can be continued. That is, since the pre-start current of the control circuit is small, the switching operation is started by the energy stored in C32 through the start resistor R31, and thereafter,
The voltage for control is supplied from the auxiliary winding P2.

[0003]

Conventionally, there are the following methods for constructing a low voltage, low current power supply in a primary circuit. One is a method of constructing a low voltage circuit by utilizing the voltage drop of a resistance like a starting resistance. Although this method is simple as a circuit with one resistor, it is difficult to provide a current supply capacity of several mA or more due to the heat generation of components. Further, in the case of a switching power supply, the auxiliary power supply can be configured by adding an auxiliary winding, but it has a supply capability only after starting the switching operation. Therefore,
Power is supplied from the starting resistor R31 at the time of normal start-up and from the auxiliary winding P2 after start-up. In this case, there are the following problems. 1. When the flyback voltage of the auxiliary winding P2 is rectified and smoothed and supplied to the control circuit. -Since the winding voltage rises slowly, the capacity of the capacitor connected to the power supply circuit must be increased, and the power supply startup time becomes longer. -The overcurrent protection when the load is short-circuited becomes the intermittent oscillation mode, and the heat generation of the output rectifier diode, choke coil, etc. may become a problem. 2. When rectifying and smoothing the forward voltage of the auxiliary winding and supplying it to the control circuit. Since the winding voltage is proportional to the input voltage, a voltage stabilizing circuit is required for the winding output in consideration of the gate breakdown voltage of the switching element (FET) and the breakdown voltage of the control IC. Control I
Considering the withstand voltage of C, a voltage stabilizing circuit is required for the winding output. Therefore, an object of the present invention is to provide an auxiliary power supply that can directly obtain a low voltage and a low current (tens of mA or more) with high efficiency directly from a commercial AC power supply, and solve the above problems.

[0004]

In order to achieve the above object, the auxiliary power supply circuit of the first invention is connected to a rectifying circuit for inputting a commercial AC voltage and outputting a pulsating voltage and an output side of the rectifying circuit. A voltage detection circuit that monitors the instantaneous value of the pulsating voltage between the smoothing capacitor and a voltage that is equal to or lower than a preset voltage, and a switch circuit that receives the detection signal and conducts and cuts off. It is equipped with. Next, an auxiliary power supply circuit according to a second aspect of the present invention includes the voltage detection circuit provided with a comparator having a hysteresis characteristic.
Next, the auxiliary power supply circuit of the third invention uses a power MOS FET for the switch circuit and has a negative feedback circuit between the output terminal and the input terminal of the voltage detection circuit.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the first invention will be described with reference to FIG. This auxiliary power supply circuit is a bridge rectifier circuit 1 that converts an input commercial AC voltage into a pulsating current, a voltage detection circuit 2 that outputs a signal when the input voltage is below a certain voltage, and a switch that cuts off or conducts a switch element by a drive signal. It is composed of a circuit 3 and a smoothing circuit 4. The bridge rectifier circuit 1 is composed of a bridge rectifier DB. The voltage detection circuit 2 is constituted by connecting a resistor R1, a Zener diode ZD1, a resistor R2, and a connection point of ZD1 and R2 to the base of a transistor Q1 connected in series, and a collector of the resistor R1 and a resistor R3 to a rectifier circuit. To be done. The switch circuit 3 includes transistors Q2 and Q3 connected in Darlington and a resistor R4 connected to its collector.
The base of the transistor Q2 connected to the rectifier circuit is connected to the collector of the transistor Q1 of the voltage detection circuit 2. The smoothing circuit 4 is
It is configured by connecting the capacitor C1 to the emitter of the transistor Q3 of the switch circuit 3. The operation will be described below. The input commercial AC voltage is converted by the bridge rectifier circuit 1 into a pulsating current voltage as indicated by v1 in FIG. 1B and supplied to the detection circuit 2 and the switch circuit 3. Rectifier output pulsating current voltage is Zener voltage VZD
When it is 1 or less, the base current of the transistor Q1 does not flow, so the transistor Q1 is cut off and the potential at the connection point between the resistor R3 and the collector of the transistor Q1, that is, the connection point between the detection circuit 2 and the switch circuit 3 becomes high level and the switch A drive current is supplied to the circuit 3. On the other hand, when the output pulsating voltage of the rectifier becomes equal to or higher than the Zener voltage VZD1, a current flows to the base of the transistor Q1 through the resistor R1 and the Zener diode ZD1, the transistor Q1 becomes conductive, and the current is not supplied to the switch circuit 3. That is, the switch circuit 3 operates so as to guide the voltage to the output only when the pulsating current voltage v1 is lower than the Zener voltage VZD1 by the signal from the detection circuit 2. Therefore, the output voltage of the switch circuit 3 is as shown in FIG. This voltage is the smoothing capacitor C1
Is converted into direct current as shown in FIG. Second
An embodiment of the invention will be described with reference to FIG. First
The difference from the embodiment of the invention is that the configuration of the voltage detection circuit 2 is changed and the overall configuration and operation are the same. The voltage detection circuit 2 includes a resistor R1-1 connected in series, a Zener diode ZD1 and a capacitor C2 connected in parallel to the Zener diode ZD1, and a (+) terminal from a connection point of the resistors R1-1 and ZD1 through R1-5. Of the comparator IC1, the resistors R1-2 and R1-3 connected to its (-) terminal, and the rough resistors R3 and R1-4 described at its output terminal. The operation of the voltage detection circuit 2 will be described. A reference voltage is generated by the resistor R-1, the Zener diode ZD1, and the capacitor C2, and is applied to the (+) terminal of the comparator IC1. On the other hand, the (-) terminal of the comparator IC1 is divided by the output voltage resistors R1-2 and R1-3 of the rectifier circuit and applied. The (+) terminal voltage and the (-) terminal voltage of the comparator IC1 are compared and output, but since the feedback resistor R1-4 is connected between the output terminal and the (+) terminal, the comparator IC
1 performs the hysteresis operation as shown in FIG. D
Reference numerals 1 and D2 are VBE reverse voltage protection diodes for the transistors Q2 and Q3 when the DC output voltage is relatively high. Next, an embodiment of the third invention will be described with reference to FIG. The difference from the second invention is that the switch element of the switch circuit 3 is from a Darlington transistor to a power MOS F
The other configuration is the same because it is changed to ET and the feedback circuit 5 is added. Switch circuit 3
Is connected from the FET whose gate is connected to the output of the voltage detection circuit and its drain to the bridge diode DB with a resistor 4 and the source thereof is connected to the smoothing capacitor C1. And diode D1 are connected in series. The feedback circuit 5 connects the DC output circuit to the resistor R
5. Transistor Q through Zener diode ZD3
4 and the collector thereof is connected to the cathode terminal of the Zener diode ZD1. By using the power MOS FET as the switch circuit, the voltage of the gate can be controlled, and the drive loss can be reduced as compared with the bipolar transistor. The Zener diode ZD2 and the diode D1 are elements for protecting the FET gate breakdown voltage. Next, the operation of the feedback circuit 5 will be described. Now, if the output DC voltage increases, the base current flowing through the transistor Q4 through the resistor R5 and the Zener diode ZD3 increases. Then, the reference voltage applied to the (+) terminal of the comparator IC decreases, which works to decrease the output voltage. As a result, the output voltage is stabilized.

[0006]

As described above, according to the present invention, a high-voltage auxiliary power supply of low voltage and low current can be constructed in the primary circuit, so that the startup time of the switching power supply can be shortened and the safety of the overcurrent protection circuit can be improved. I can. In addition, it is possible to eliminate the start-up resistance that generates a large amount of heat and the transformer winding for the auxiliary power supply. Furthermore, the present invention can be applied not only to the switching power supply but also to the low-voltage low-current power supply circuit of the primary circuit without using an AC transformer or the like.

[Brief description of drawings]

FIG. 1A is a circuit diagram showing an embodiment of the first invention.

FIG. 1 (b) shows waveforms of the input voltage and the rectifier circuit output voltage v1 of FIG. 1 (a).

FIG. 1C is an ON state of the transistor Q1 of FIG.
The OFF timing is shown.

FIG. 1D is an ON state of the transistor Q3 of FIG.
The OFF timing is shown.

FIG. 1 (e) shows an output voltage waveform when there is no C1 in FIG. 1 (a).

FIG. 1 (f) shows an output voltage waveform when C1 of FIG. 1 (a) is connected.

FIG. 2 (a) is a circuit diagram showing an embodiment of the second invention.

2 (b) shows waveforms of the input voltage and the rectifier circuit output voltage v1 of FIG. 2 (a).

FIG. 2 (c) is an ON state of the transistor Q1 of FIG. 2 (a),
The OFF timing is shown.

FIG. 2 (d) shows an output voltage waveform when C1 in FIG. 2 (a) is not present and an output voltage waveform when C1 is connected.

FIG. 3 is a circuit diagram showing an embodiment of the third invention.

FIG. 4A is a circuit diagram showing a conventional example.

FIG. 4 (b) shows the control circuit Vcc voltage of FIG. 4 (a).

[Explanation of Codes] 1 Rectifier circuit 2 Voltage detection circuit 3 Switch circuit 4 Smoothing circuit 5 Negative feedback circuit 6 Starting circuit 7 Auxiliary power supply circuit

Claims (3)

[Claims] 1. An instantaneous value of a pulsating voltage is monitored and preset between a rectifying circuit that inputs a commercial AC voltage and outputs a pulsating voltage and a smoothing capacitor connected to the output side of the rectifying circuit. An auxiliary power supply circuit, comprising: a voltage detection circuit that generates a signal when the voltage is equal to or lower than a predetermined voltage; and a switch circuit that receives and detects a detection signal and performs a conduction / cutoff operation. 2. The auxiliary power supply circuit according to claim 1, wherein the input / output response of the voltage detection circuit has a hysteresis. 3. A power MOS FE for the switch circuit.
The auxiliary power supply circuit according to claim 1, further comprising a negative feedback circuit provided between the output terminal and the input terminal of the voltage detection circuit while using T.