JPH0567148U - Slow start-up circuit for power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a slow start-up circuit for a power supply having a stable startup characteristic with small load dependency. An error that outputs an error voltage signal by comparing a switching power supply unit, voltage dividing resistors R1 and R2 having one ends connected to an output voltage line, and a voltage divided by the voltage dividing resistors with a reference voltage In a switching power supply device that includes an amplifier 10 and a pulse width control circuit 20 that sends a switching control signal to a switching element in a direction in which this error voltage signal decreases, a capacitor C3 having one end connected to an output voltage line, A slow start circuit 30 having a resistor R3 connected to the other end of the capacitor C3 and grounded at the other end, and a diode D3 connecting the intermediate point of the CR series circuit and the intermediate point of the voltage dividing resistor is provided. Is characterized by.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a stabilized power supply device used for measuring instruments and the like, and more particularly to a device in which a rising speed of an output voltage is limited due to an inductive load or the like.

[0002]

[Prior Art]

 The applicant of the present invention has proposed a slow start-up circuit for limiting the inrush current in, for example, Japanese Utility Model Laid-Open No. 2-33548. FIG. 6 is a circuit diagram of a conventional device. In the figure, an AC current sent from a commercial AC power supply AC is rectified by a rectifier circuit such as a diode bridge DB, smoothed by a capacitor C1 and applied to a primary winding n1 of a transformer T. A switching Q such as an FET is connected to the primary winding n1 and is controlled to be turned on and off by the pulse width control circuit 10. Since a switching signal is induced in the secondary winding n2 of the transformer T, it is rectified by the rectifying circuit of the diodes D1 and D2, the high frequency component is removed by the choke coil L, and it is converted to direct current by the capacitor C2, and output. The voltage Vout is supplied to the load side.

In order to stabilize the output voltage, the output voltage Vout is input to one terminal of the error amplifier using the voltage dividing resistors R1 and R2. The error amplifier 10 compares the divided output voltage Vout with the reference voltage Vref and outputs an error signal. The pulse width control circuit 20 adjusts the switching control signal in the direction of reducing the error signal and sends it to the switching element Q. The pulse width control circuit 20 receives the oscillation signal OSC from the outside and adjusts the switching pulse width by the error signal. The slow start circuit may destroy the switching element Q when the switching element Q is turned on and off in the state where the inrush current is generated, and thus the operation of the switching element Q is suppressed during such a period. Here, it is realized by a time constant circuit of CR, and the spreading speed of the pulse width is suppressed.

[0004]

[Problems to be Solved by the Invention] However, since the output voltage stabilization loop is cut off during operation of the slow start circuit, the rise of the output voltage is caused by the spread of the pulse width allowed by the slow start circuit. Will be determined by. Therefore, there was a problem that the startup speed varied greatly depending on the type of power supply. Also, with a power supply with a high switching frequency, it is difficult to stably output extremely thin pulses, so there was the problem that rising control becomes even more difficult.

The present invention solves such a problem, and an object of the present invention is to provide a slow start-up circuit for a power supply having a stable startup characteristic with little load dependency.

[0006]

[Means for Solving the Problems]

 The present invention, which achieves the above object, rectifies and smoothes an alternating current supplied from a commercial power source, applies it to the primary winding of a transformer, and turns it on and off with a switching element to generate switching in a secondary winding of a transformer. A switching power supply unit that rectifies and smoothes a current and outputs a predetermined voltage, a resistor R1 whose one end is connected to an output voltage line, and a resistor R2 whose one end is connected to the other end and which is grounded at the other end. The voltage dividing resistor is compared with the voltage divided by the voltage dividing resistor and the reference voltage, and the error amplifier 10 that outputs an error voltage signal and the switching element in the direction in which the error voltage signal decreases In a switching power supply device having a pulse width control circuit 20 for sending a switching control signal to the capacitor C3, one end of which is connected to the output voltage line, and the capacitor C3. A slow start circuit 30 having a resistor R3 connected to one end and the other end grounded, and a diode D3 connecting the intermediate point of the CR series circuit and the intermediate point of the voltage dividing resistor is provided. ..

[0007]

[Action]

 The basic configuration of the power supply device is a normal stabilized switching power supply. Since the starter circuit 30 is provided in parallel with the voltage dividing resistor, it is inside the output voltage stabilizing loop. Therefore, the power supply has a stable rising characteristic regardless of the load state.

[0008]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, components having the same functions as those in FIG. 6 are designated by the same reference numerals and the description thereof will be omitted. In the figure, the slow start circuit 30 is provided in parallel with the voltage dividing resistors R1 and R2. One end of the capacitor C3 is connected to the output voltage line. The resistor R3 has one end connected to the other end of the capacitor C3 and the other end grounded. Since the output voltage Vout is positive here, the polarity of the diode D3 is such that the anode terminal is connected to the capacitor C3 side and the cathode terminal is connected to the voltage dividing resistor side. For negative voltage, reverse polarity.

The characteristics of the device thus configured will be described below. FIG. 2 is a circuit diagram of an error amplifier 10 of a stabilized power supply having a usual feedback. An input resistor Ri is connected to the negative terminal and has a feedback resistor Rf. Here, consider the case where the capacitor Cf is connected in parallel with the feedback resistor Rf. Seen from the input side, the circuit having the capacitor Cf connected in parallel is an integral type, and even if the reference voltage Vref is a step function, the output voltage is exponentially functioned by appropriately selecting the value of CfRf. Can be raised to. On the other hand, when the capacitor Cf is connected to the feedback resistor Rf, the lead phase is input to the error amplifier 10. Therefore, the state in which the capacitor Cf is always connected is not preferable for phase compensation. For example, in the low frequency region, the total system becomes a first-order advance, and low frequency ramp-like oscillation may occur depending on the circuit.

FIG. 3 is a circuit diagram of the error amplifier 10 in the embodiment of FIG. Here, it is effective only when the power is turned on and the capacitor Cf (C3) is charged, and the diode D3 is connected for disconnecting it in the steady state. After the capacitor Cf is charged, the anode terminal of the diode D3 becomes zero potential due to the resistor R3, and the capacitor Cf becomes invalid for the error amplifier 10.

FIG. 4 is an operation explanatory diagram of the circuits of FIGS. 2 and 3, where (A) represents the reference voltage Vref and (B) represents the output voltage Vo. When the power is turned on, the reference voltage Vref changes stepwise, but the voltage output from the error amplifier 10 gradually increases due to the time constant of CfRf to display the original error voltage.

FIG. 5 is a circuit diagram showing a modified embodiment of the present invention. A shunt regulator D6 is used as the error amplifier 20. The circuit of the resistor R4 and the capacitor C4 is connected in parallel with the resistor R1 for phase compensation. An error voltage signal is transmitted to the pulse width control circuit 20 using a photocoupler PC in order to insulate the primary side from the secondary side. The photocoupler PC is connected to the power supply line Vcc via the current limiting resistor R5.

[0013]

[Effect of the device]

 As described above, according to the present invention, the slow start circuit 30 is placed in the output voltage stabilization loop so that it operates only when the power is turned on. Therefore, the rising characteristic is determined regardless of the load connected to the power source. It has a practical effect.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a regulated power supply error amplifier 10 with normal feedback.

3 is a circuit diagram of an error amplifier 10 in the embodiment of FIG.

FIG. 4 is an operation explanatory diagram of the circuits of FIGS. 2 and 3;

FIG. 5 is a circuit diagram showing a modified embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional device.

[Explanation of symbols]

 10 Error Amplifier 20 Pulse Width Control Circuit 30 Slow Start Circuit

Claims (1)

[Scope of utility model registration request] 1. An AC current supplied from a commercial power source is rectified and smoothed, applied to a primary winding of a transformer, turned on and off by a switching element, and a switching current generated in a secondary winding of the transformer is rectified and smoothed. A switching power supply unit that outputs a predetermined voltage, a resistor R1 whose one end is connected to an output voltage line, and a resistor R1.
1 is connected to the other end and one end is connected to the grounded resistor R2, and the voltage divided by this voltage dividing resistor is compared with the reference voltage.
An error amplifier 10 that outputs an error voltage signal, and a pulse width control circuit 20 that sends a switching control signal to the switching element in the direction in which the error voltage signal becomes smaller are provided. A capacitor C3 connected to the capacitor C3, a resistor R3 having one end connected to the other end of the capacitor C3 and the other end grounded, and a diode D3 connecting the midpoint of the CR series circuit and the midpoint of the voltage dividing resistor. A slow start-up circuit for a power supply, which is provided with the slow start circuit 30.