JP2513544Y2 - Switching regulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a switching regulator having a protection circuit that protects a control circuit that controls a main switching element from a short circuit of the main switching element.

[Conventional technology]

A known protection circuit for this type of conventional switching regulator is shown in FIG. 2 (Japanese Patent Laid-Open No. 7977/1990).
No. 1). In the figure, the switching regulator comprises a DC power supply 1, a transformer 2, a main current circuit 3, a control circuit 4, an output circuit 5, a protection circuit 6, and the like. The DC power supply 1 applies the AC power supply 7 to the rectifying / smoothing circuit 9 via the current fuse 8, converts the AC power supply 7 into a DC voltage by the rectifying / smoothing circuit 9, and supplies power to this switching regulator. The transformer 2 has a primary coil 2a, an output coil 2b, and the like. The primary coil 2a, the transistor 10 whose collector is connected to the primary coil 2a, and the current detection resistor 11 connected to the emitter of this transistor 10 are the main currents. The circuit 3 is configured so that one end of the primary coil 2a is connected to the positive terminal of the DC power supply 1 and one end of the current detection resistor 11 is connected to the negative terminal of the DC power supply 1 for power supply. The base of the transistor 10 is supplied with a drive pulse from the control circuit 4 so as to keep the output voltage stable in accordance with variations in the input voltage and the output voltage. The drive pulse causes the transistor 10 to perform on / off switching. To work. As a result, a voltage pulse is taken out from the output coil 2b of the transformer 2 and input to the output circuit 5, so that a stabilized output voltage is obtained at the output terminals 13 and 13.

The protection circuit 6 is composed of three diodes connected in series so that the anode is on the base side of the transistor 10 and the cathode is on the other end of the current detection resistor 11 connected to the emitter of the transistor 10. . And
When the transistor 10 is in a normal switching operation state, the three diodes that form the protection circuit 6 are the sum of the base-emitter voltage of the transistor 10 and the voltage across the current detection resistor 11 generated by the emitter current. Is selected such that the sum of the forward voltage drops of those three diodes is sufficiently large.

When a failure such as destruction of the transistor 10 occurs in this way, a large current flows through the current detection resistor 11 due to a short-circuit between the collector and the base, and the voltage across the current detection resistor 11 rapidly increases. The diode is rendered conductive to prevent the potential of the control circuit 4 from rising to prevent chain breakage and heat generation in the circuit portion, and at the same time, the current fuse 8 on the input side is melted by a short-circuit current to ensure safety.

[Problems to be solved by the device]

In such a conventional device, it is necessary to select a diode of the protection circuit that has a large surge current withstand current and a large forward voltage drop during normal operation. Furthermore, there are disadvantages that several such diodes must be connected in series, the number of parts increases, and the mounting position on the printed wiring board must be secured. Such a problem is that when the switching transistor is a field effect transistor (hereinafter abbreviated as FET), the gate threshold voltage becomes high, so the number of diodes in the protection circuit is accordingly large, for example, gated. If the threshold value is 4V, there is a problem that 6 diodes must be used.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the conventional device and provide a switching regulator provided with a protection circuit that operates reliably with simple elements.

[Means for solving the problem]

In order to achieve the above-mentioned object, the present invention provides an AC power supply through a transformer having a primary coil and an output coil, a main current circuit in which the primary coil, a main switching element and a current detection resistor are connected in series, and a current fuse. A DC power supply that rectifies and supplies power to the main current circuit, a control circuit that supplies a drive pulse to the gate of the main switching element to control the switching operation of the main switching element, and converts the output voltage of the output coil into a DC voltage. It is connected in parallel to an output circuit that detects this voltage and performs a stable operation of the control circuit and a series circuit of the main switching element and the current detection resistor, and a gate is connected to a connection point between the main switching element and the current detection resistor. It is characterized by having a thyristor.

[Embodiment of Device]

In this invention, the protection circuit is composed of a thyristor having a gate connected to a connection point between the main switching element and the current detection resistor, which is connected in parallel to a series circuit of the main switching element and the current detection resistor. When a failure such as a short circuit occurs, the thyristor becomes conductive due to the voltage drop of the current detection resistor, and the current fuse on the power supply side is blown by the conduction of this thyristor.

〔Example〕

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a connection diagram showing an embodiment of a switching regulator according to the present invention. In FIG. 1, the same parts as those of the conventional device shown in FIG. 2 are designated by the same reference numerals.

In FIG. 1, the switching regulator is composed of a DC power source 1, a transformer 2, a main current circuit 3, a control circuit 4, an output circuit 5 and the like as in the conventional one. A protection circuit different from the circuit 6 is provided. The DC power supply 1 converts the AC power supply 7 into a DC voltage by the rectifying / smoothing circuit 9 via the current fuse 8 as in the conventional one, and supplies power to this switching regulator. The transformer 2 has a primary coil 2a, an output coil 2b, etc. The primary coil 2a, the drain is connected to one end of the primary coil 2a, and the source is connected to one end of the current detection resistor 11 The main current circuit 3 is configured so that the other end of the primary coil 2a is connected to the plus terminal of the DC power supply 1 and the other end of the current detection resistor 11 is connected to the minus terminal, respectively, for power feeding. The gate of the FET 10a is supplied with a driving pulse from the control circuit 4 so as to keep the output voltage stable according to the fluctuation of the input voltage. Further, the voltage of the output circuit 4 described below is the voltage detection circuit 14, the photocoupler. The drive pulse of the control circuit 4 is controlled via 15. Further, at the time of start-up or output short circuit, the drive pulse of the control circuit 4 is controlled by the overcurrent detection value inputted from the current detection resistor 11 to the current detection resistor 11 so that the overcurrent does not flow. In this way, a voltage pulse is taken out from the output coil 2b of the transformer 2 and input to the output circuit 5, so that a stabilized voltage is obtained from the output terminals 13 and 13.

In this embodiment, the protection circuit is composed of a thyristor 17 connected in parallel with the series circuit of the FET 10a and the current detection / detection resistor 11, and the gate of the thyristor 17 is connected to the FET 1 via the resistor 18.
It is connected to the connection point between 0a and the current detection resistor 11.

When the FET10a is destroyed due to an open failure on the load side or a failure of the overcurrent protection function of the control circuit 4, the FET10a eventually becomes short-circuited between the drain and source, and when a large current flows through the current detection resistor 11, the current Since the voltage drop across the detection resistor 11 becomes high, an ignition current flows through the gate of the thyristor 17 via the resistor 18 and the thyristor 17 becomes conductive. As a result, the short circuit current Is of the main current circuit 3 flows through the thyristor 17, the current fuse is blown by the short circuit current Is, the control circuit 4 and the photocoupler 15 are protected from overcurrent, and chain breakage of these occurs. To be prevented.

[Effect of device]

As described above, according to the present invention, a transformer having a primary coil and an output coil, a main current circuit in which the primary coil, a main switching element, and a current detection resistor are connected in series, and an AC power source through a current fuse. A DC power supply that rectifies and supplies power to the main current circuit, a control circuit that supplies a drive pulse to the gate of the main switching element to control the switching operation of the main switching element, and converts the output voltage of the output coil into a DC voltage. It is connected in parallel to an output circuit that detects this voltage and performs a stable operation of the control circuit and a series circuit of the main switching element and the current detection resistor, and a gate is connected to a connection point between the main switching element and the current detection resistor. By providing a built-in thyristor, it is possible to prevent chain breakage of the control circuit and photocoupler with a simple protection circuit. Inexpensive and space for mounting the printed circuit board of the protection circuit has the effect that is reduced.

[Brief description of drawings]

FIG. 1 is a wiring diagram showing an embodiment of a switching regulator according to the present invention, and FIG. 2 is a wiring diagram showing an example of a conventional switching regulator protection circuit. 1: DC power supply, 2: Transformer, 2a: Primary coil, 2b: Output coil, 3: Main current circuit, 4: Control circuit, 5: Output circuit, 8: Current fuse, 10: Switching transistor, 10a: FET, 17:
Thyristor.

Claims (1)

(57) [Scope of utility model registration request] 1. A transformer having a primary coil and an output coil,
A main current circuit in which the primary coil, a main switching element, and a current detection resistor are connected in series, a DC power source that rectifies an AC power source through a current fuse to supply power to the main current circuit, and a drive pulse to the gate of the main switching element. And a control circuit for controlling the switching operation of the main switching element, an output circuit for converting the output voltage of the output coil into a DC voltage and detecting this voltage for stable operation of the control circuit, and the main switching element. A switching regulator comprising a thyristor connected in parallel to a series circuit with a current detection resistor and having a gate connected to a connection point between the main switching element and the current detection resistor.