JPS633613A - Overcurrent protective circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention detects the increase in load current due to a short circuit in the load due to some factor, stops the oscillation of the switching power supply, and supplies the load to the load. This invention relates to an overcurrent protection circuit that stops the supply of current to prevent parts from burning out.

2. Description of the Related Art Conventionally, in television receivers, short-circuit tests are required between bins of flyback transformers, pulse transformers, etc. based on the Electrical Appliance and Material Control Law. Measures were taken to prevent significant smoke and fire from occurring during this short test.

Conventional technology involves inserting an overcurrent protection circuit between the 116V output line of the power supply and the 116V input line of the flyback transformer, and when the power supply current increases abnormally, the protection circuit operates by detecting it. This was to stop horizontal oscillation. The conventional protection circuit described above will be explained below with reference to the drawings.

In Fig. 3, 1 is a thyristor for controlling a switching power supply, 2 is a power supply start circuit, 3 is a thyristor control circuit,
4 is an overcurrent detection circuit, 5 is an overcurrent detection transistor, 6
1 is a thyristor for overcurrent detection, 4 is a switching transistor, 8 is a flyback transformer, and 9 is a resistor.

When the power is turned on, a gate current flows from the power start circuit 1 to the thyristor 1, the thyristor 1 becomes conductive, and power is supplied to the flyback transformer 8. When power is supplied to the flyback transformer 8, a horizontal pulse (approximately 2
5VOp) is generated, and the pulse is fed back to the thyristor control circuit 3 to control the power supply.

Here, when the current in the power supply (116V) line of the fly bank transformer 8 increases due to a factor such as a load short, the voltage drop across the overcurrent detection resistor 9 increases. This voltage drop is 0
．． When the voltage exceeds 6V, the transistor 5 becomes conductive, a gate current flows through the thyristor 6, and the thyristors become conductive. When the thyristors become conductive, the transistor 7 becomes conductive and the operation of the horizontal oscillation circuit (not shown) is stopped.

Problems to be Solved by the Invention However, the above-mentioned configuration has the problem of increasing the number of parts and increasing costs.

In view of the above-mentioned problems, the present invention provides an entire overcurrent protection circuit that can be realized at low cost with a small number of parts.

Means for Solving the Problems In order to solve the above problems, the overcurrent protection circuit of the present invention uses a resistor to detect the current in the power supply line that has increased due to a short circuit in the load circuit, etc. This switches the transistor to disable the operation of the power supply start circuit, thereby stopping the operation of the power supply control thyristor, thereby lowering the voltage of the power supply line and preventing the parts from smoking and catching fire.

Effect The present invention has the above-mentioned configuration, and has the following advantages compared to the conventional embodiments.
With half the number of parts and cost, it is possible to detect overcurrent, stop the oscillation of the power control thyristor, and prevent parts from smoking or catching fire.

Embodiment Hereinafter, an overcurrent protection circuit according to an embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 shows an overcurrent protection circuit in one embodiment of the present invention.

1 is a thyristor for controlling a switching power supply, 2 is a power supply start circuit, 11 is a fuse resistor included in the power supply start circuit 2, 3 is a thyristor control circuit, 4 is an overcurrent detection circuit, and 5 is an overcurrent detection transistor. Turned on by transistor 5.

This is a switching transistor that is controlled to be off, and has its emitter grounded and its collector connected to the connection point between the fuse resistor 11 and the diode 12.

9 is an overcurrent detection resistor, 10 is a Zener diode for preventing malfunction, and 8 is a flyback transformer. Also 13
is a smoothing capacitor.

In the above configuration, let us now consider the case where the load (secondary side) of the flyback transformer 8 is short-circuited.The current on the secondary side of the flyback transformer 8 increases abnormally, and the primary side power supply (B2 = 116V) The line current also increases.As the primary side current increases, the core of the flybank transformer 8 will eventually become saturated, making it impossible to obtain a horizontal collector pulse with a sufficient peak value.Horizontal collector When pulses are no longer obtained, pulses that are fed back to the thyristor control circuit 3 to control the thyristor 1 are also no longer obtained, making it impossible to change the thyristor 1 from a non-conducting state to a conducting state.

Figure 2 shows the anode of thyristor 1 at that time (power supply B2 =
11 ev line), and when a load short circuit occurs, the thyristor 1 becomes non-conductive, so the cathode voltage drops from A to B in FIG.

However, when the cathode voltage reaches θOv, the diode of the power supply start circuit 2 becomes conductive and a gate current flows, and the thyristor 1 becomes conductive and the cathode voltage of the thyristor 1 becomes B.
to C (1167). Then again from C to D
descends to. This repetition is performed at the discharge time constant of the smoothing capacitor 13.

On the other hand, when the current in the power supply line (116 V) increases and the current flowing through the resistor 9 exceeds 1.6 A i-, the transistor 5 becomes conductive and the Zener diode 10 becomes conductive. When the Zener diode 1Q becomes conductive, a pace current flows through the transistor and the transistor becomes conductive. When the transistor is turned on, the AC rectified output voltage 125V falls to the ground via the fuse resistor 11, so that the fuse resistor 11 is disconnected in 2 to 3 seconds. When the fuse resistor 11 is disconnected, when the cathode voltage of the thyristor 1 reaches point B in FIG. 2, the cathode voltage (voltage "2") drops to OV because no gate current flows.

When the power supply B2 voltage of the flybank transformer 8 becomes OV, the secondary output voltage of the flybank transformer 8 becomes Ov, so that smoking and burning of the parts can be prevented.

Furthermore, since the power supply start circuit 2 is opened, the power supply will not be restored again, which is advantageous in terms of safety.

Effects of the Invention As described above, according to the present invention, it is possible to detect overcurrent, completely stop oscillation of the power control thyristor, and prevent parts from smoking and catching fire with half the number of parts and cost compared to conventional circuits. can.

[Brief explanation of drawings]

No. 1 is a circuit diagram of an overcurrent protection circuit in one embodiment of the present invention, and FIG. 2 is a circuit diagram of an overcurrent protection circuit in an embodiment of the present invention.
2 (116v) line voltage waveform diagram, and FIG. 3 is a circuit diagram of a conventional overcurrent protection circuit. 1... Thyristor for controlling the switching source,
2...Power supply start circuit, 3...Thyristor control circuit, 4...Overcurrent detection circuit, 5...
... Overcurrent detection transistor, 7 ... Switching transistor, 8 ... Fly bank transformer, 9 ... Overcurrent. current detection resistor, 10... Zener diode for malfunction prevention, 11... fuse resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure (Star Toro) from each)

Claims (1)

[Claims] A control circuit that controls the conduction angle of the thyristor to supply a stabilized power supply voltage to the load, a power start circuit that supplies a start current to the gate of the thyristor when the power is turned on, and a power supply start circuit that is inserted into the power output line of the thyristor. an overcurrent protection circuit comprising: a load current detection resistor; and a switching element that conducts by a voltage across the resistor to ground a fuse resistor included in the power supply start circuit when the load current increases abnormally.