JPH058761Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a primary side chopper control type DC stabilized power supply device. In particular, it relates to short-circuiting means for the inrush prevention resistor.

[Background of the idea]

Conventional primary side chopper control type DC stabilized power supplies have the disadvantage that the circuit for protecting the inrush prevention resistor is complicated.

This point will be explained with reference to FIG. This conventional device consists of an inrush prevention resistor 3 that prevents an excessive charging current from flowing into the capacitor 8 when an AC power supply 1 is turned on, a short-circuit thyristor 2 that shorts the inrush prevention resistor 3 after oscillation, and an AC output from the AC power supply 1. It includes a rectifier 4 that rectifies the .

The primary side chopper circuit of this conventional device includes a switching transistor 9 and a smoothing chopper circuit 21.
and capacitor 20, flyhole diode 15, drive circuit 10 of transistor 9, current transformer 13 for overcurrent protection, diodes 19 and 1
2. It consists of capacitors 11 and 17, resistors 14, 16, 18, etc.

The primary chopper circuit operates as follows. The output voltage (voltage between A and A') is compared with the reference voltage 27, an error is detected by the differential amplifier 26, and the PWM
The control circuit 24 sets the conduction period of the transistor 9 and switches the transistor 9 via the drive circuit 10. In this way, the DC voltage of the capacitor 20 after the primary chopper circuit stage is controlled to be constant, converted to a predetermined DC voltage by the non-controlled DC-DC converter 22, and the constant output voltage is applied to the load circuit through the smoothing circuit 23. Output to.

On the other hand, protection against overcurrent on the load circuit side is performed by detecting the output current based on the magnitude of the voltage drop across the resistor 28. When the current exceeds a certain level, it controls the PWM control circuit 24 via the comparator 25, thereby lowering the output voltage and protecting the circuit.

The power supply device operates as described above, but if the short-circuit thyristor 2 in parallel with the inrush prevention resistor 3 is left in its initial non-conducting state during operation (including overcurrent operation), the inrush prevention resistor 3 3 becomes overloaded and burnt out. Therefore, the current flowing through the flyhole diode 15 is detected through the current transformer 13,
By rectifying the voltage with a diode 19 and inputting it to the gate of the short-circuiting thyristor 2 via the resistor 18, the rush prevention resistor 3 is short-circuited with the thyristor 2.

By the way, when the current transformer 13 having an inductance component is inserted into the flyhole diode 15, the rise time of switching is delayed and switching loss is increased. As a countermeasure, current is caused to flow through the diode 12 and capacitor 11 at the beginning of the turn-on operation to speed up the rise. After that, a current is passed through the current transformer 13 and the flyhole diode 15.

Note that the resistors 14 and 16 and the capacitor 17 are for preventing discharge and spike voltage. The transformer 5, rectifier 6, and smoothing capacitor 7 are
A drive power supply circuit for the PWM control circuit 24 is configured.

[Purpose of invention]

The purpose of the present invention is to easily provide protection for the inrush prevention resistor in a primary side chopper control type DC stabilized power supply device.

[Summary of the idea]

In the present invention, the voltage of the oscillation transformer in the converter circuit is used to conduct the thyristor for shorting the inrush prevention resistor.

Further, an overcurrent detection signal is received via an insulated signal transmission element, and the short circuit thyristor is forcibly made conductive.

[Example of idea]

An embodiment of the present invention will be described below with reference to FIG. For parts similar to those shown in FIG. 1, the component numbers in the circuit shown in FIG. 1 are used as they are.

In the DC stabilized power supply device of this embodiment, AC output from an AC power supply 1 is supplied to rectifying and smoothing circuits 4 and 8 via an inrush prevention resistor 3 and a short-circuiting thyristor 2 parallel to the inrush prevention resistor 3. Further, the DC output from the rectifying and smoothing circuits 4 and 8 is supplied to the load via a chopper circuit and further via a converter circuit.

The chopper circuit includes a switching transistor 9, its drive circuit 10, and a smoothing transistor 2.
1, a capacitor 20, a flyhole diode 15, etc.

The converter circuit includes another switching transistor 41, its drive circuit 40, an oscillation transformer 34, a rectifying diode 44, a flyhole diode 42, and the like. The oscillation transformer 34 includes a primary winding 37, a secondary winding 38, a reset winding 36, and further includes a detection winding 35.
The detection winding 35 is for controlling the short circuit thyristor 2 and has no relation to the original function as a converter.

Flyhole diode 4 after converter
3. The smoothing circuit 45 and the capacitor 46 constitute a smoothing circuit. The resistor 28 and comparator 25 are used to generate an overcurrent detection signal indicating an overcurrent in the load circuit, and control circuits 24 and 10 are provided for controlling the chopper circuit in response to this signal. The configuration in this respect is the same as in FIG.

The voltage of the detection winding 35 of the oscillation transformer 34 in the converter circuit is applied via the resistor 32 and diode 33 to the gate of the short-circuiting thyristor 2 to make it conductive. When the power is turned on,
Inrush current is prevented by supplying power to the rectifying and smoothing circuits 4 and 8 through the inrush prevention resistor 3. When the power supply voltage reaches a certain voltage, the chopper circuit and the converter circuit operate, inducing a voltage in the detection winding 35 of the oscillation transformer 34. The voltage is applied as a turn-on signal to the gate of the shorting thyristor 2 via the resistor 32 and diode 33, thereby making the thyristor conductive. This protects the rush prevention resistor 3.

By the way, if the load terminals B-B' are short-circuited or an overload occurs, the comparator 25 operates due to the voltage drop across the overcurrent detection resistor 28, and the PWM control circuit 2
4. Throttle the output of the chopper circuit via the drive circuit 10. Then, the voltage generated in the detection winding 35 becomes low, making it impossible to operate the short-circuit thyristor 2. Thus, current flows continuously through the inrush prevention resistor 3, causing the resistor 3 to burn out. Therefore, in practice, countermeasures are required to address this issue.

In the present invention, forced circuits 30, 31, and 47 are provided that receive an overcurrent detection signal via an insulated signal transmission element 31 such as a photocoupler, and forcibly conduct the short circuit thyristor 2 in the event of an overcurrent. This point will be explained in more detail below. The overcurrent detection signal appearing at the output terminal of the comparator 25 is input to the light emitting section 31-b of the phototriax 31 via the resistor 47. On the other hand, the triac 31-a, which is the light receiving portion, is inserted between the anode gates of the shorting triac 2 via the resistor 30.
Thus, in the event of an overcurrent, the phototriac 31, which is a type of photocoupler, operates. As a result, a gate current is supplied to the short-circuiting thyristor 2 through the light-receiving section triax 31-a and the resistor 30, thereby making the thyristor 2 conductive and preventing the inrush prevention resistor 3 from being burnt out. The drive power supply circuits 5, 6, and 7 of the PWM control circuit 24 are also used as drive power supplies for the series circuit of the resistor 47 and the light emitting section 31-b.

[Effect of idea]

The present invention utilizes the voltage of the oscillation transformer in the converter circuit to provide a simple method for making the short-circuit thyristor conductive.

However, due to the primary side chopper control, this alone is insufficient and requires the addition of an overcurrent response type forcing circuit. Since it can be used for multiple purposes, it is generally inexpensive.

On the other hand, since the short-circuit thyristor operates using the voltage of the oscillation transformer and the overcurrent detection signal, the protection of the inrush prevention resistor is reliable.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional device, and FIG. 2 is a circuit diagram of the device of the present invention. 1...AC power supply, 2...Short circuit thyristor, 3
... Rush prevention resistor, 4 ... Rectifier, 8 ... Smoothing capacitor, 9 ... Transistor for chopper circuit, 10 ... Drive circuit, 28 ... Resistor for overcurrent detection, 25 ... Comparator, 31... Insulated signal transmission element, 34... Oscillation transformer of converter circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] AC output from an AC power source is supplied to a rectifying and smoothing circuit via an inrush prevention resistor and a short-circuiting thyristor parallel to this, and DC output from the rectifying and smoothing circuit is supplied to a chopper circuit, and further In a DC stabilized power supply device provided with a control circuit that supplies power to a load via a converter circuit and controls the chopper circuit in response to an overcurrent detection signal indicating overcurrent in the load circuit, an oscillation transformer in the converter circuit is provided. The voltage of the detection winding is applied to the gate of the short-circuit thyristor so as to make it conductive, and the overcurrent detection signal is received via an insulated signal transmission element such as a photocoupler, and the short-circuit thyristor is A DC stabilized power supply device characterized by being provided with a forced circuit that forces a thyristor to conduct.