JPH064158A - Abnormal heating prevention circuit - Google Patents

Abstract

PURPOSE:To suppress heating and to secure safety by setting the potential on the input side of a constant voltage IC at a ground level or a value near to it by energizing a Zener diode connected between the input and the output terminals of the IC when heat is generated in the constant voltage IC by overloading. CONSTITUTION:When the output side of the constant voltage IC 55 is short- circuited to the ground due to an unknown reason, for example, the generation of the short-circuit between electrodes in an output capacitor C2, or the output current value of the constant voltage IC 55 goes to an excessive value due to the overloading in a stabilized DC voltage supply circuit 3, a voltage to be impressed between the cathode and anode of the Zener diode ZD2 exceeds a Zener voltage, which energizes the Zener diode ZD2, and the input side of the constant voltage IC 55 drops to the ground potential. Therefore, the power-on signal output terminal P-OH of a microcomputer 54 goes to an 'L' level. A switching transistor Q10 is turned off at the timing of the fall of the 'L' level, and a relay contact 58a is opened, which stops the operation of a power source circuit 60.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage integrated circuit (hereinafter referred to as a constant voltage IC) for stabilizing a direct current power source used in electronic equipment, etc. The present invention relates to a possible abnormal heat generation prevention circuit.

[0002]

2. Description of the Related Art FIG. 2 illustrates a conventional technique by using a constant voltage IC used in a television apparatus or the like. In the figure, 51 is a flyback transformer, 52 is a horizontal drive and horizontal power circuit for supplying horizontal oscillation power to the primary side of the flyback transformer 51, and 53 is an'H 'level power-on signal output from a microcomputer 54. Is a switch circuit for supplying the voltage on the primary side of the flyback transformer to the constant voltage integrated circuit 55, and 56 converts the voltage generated on the secondary side of the flyback transformer 51 into direct current by the constant voltage IC 56a and stabilizes it. This is a stabilized DC voltage supply circuit for supplying to a tuner or the like.

Reference numeral 57 is a back-up circuit, Q10 is a switching transistor which operates a relay circuit 58 by a power-on signal output from the microcomputer 54 to close a relay contact 58a, and 59 is a rectifier circuit which converts AC power into DC. .

Reference numeral 60 denotes a power supply circuit, which is a circuit for generating and outputting a predetermined DC voltage. The output of the flyback transformer high-voltage generating circuit boosts or lowers the horizontal oscillation output by the flyback transformer 51, and further converts it into a DC voltage of various magnitudes.

First, the horizontal retrace line pulse is boosted and rectified to generate the anode voltage between the images and the focus voltage from the secondary coil, and the voltage of the primary coil is directly rectified and supplied to the video output circuit. The voltage is generated by the constant voltage integrated circuit 55. Further, the voltage in the scanning period is converted into a DC voltage stabilized by the constant voltage integrated circuit 56a and supplied to the tuner and the video intermediate frequency circuit.

[0006]

As described above, the constant voltage ICs 55 and 56a are used to convert the output into a stable direct current. However, the output side of the constant voltage IC drops to the ground for some reason, Alternatively, when an overload occurs, the current limiting circuit operates in the constant voltage IC and the function of suppressing the output current works. At this time, a part of the input is consumed as heat inside the constant voltage IC and the output current is suppressed, so that the constant voltage IC itself generates heat. Therefore, a large heat sink is used for the purpose of efficiently releasing heat to the outside and ensuring safety.

As a result, when mounting the circuit components on the board, sufficient consideration must be given to minimize the thermal effect on other components. Further, when mounting the components on the board There was a problem that efficiency deteriorated.

Further, in the case of using the constant voltage IC 56a, since an overcurrent flows from the flyback transformer, there is a problem that the flyback transformer itself also generates heat.

The present invention has been made to solve the above problems, and an object of the present invention is to promptly suppress heat generation of a constant voltage IC due to overload and ensure safety. It is an object of the present invention to provide an abnormal heat generation prevention circuit.

[0010]

SUMMARY OF THE INVENTION An abnormal heat generation prevention circuit according to the present invention is a circuit for obtaining a DC power supply by a constant voltage IC, and a zener diode connected between the input and output terminals of the constant voltage IC and the constant voltage IC. And an electric power supply stopping means for stopping the electric power supplied when the electric potential on the input side of the input terminal becomes the ground level or a value close to the ground level.

[0011]

The abnormal heat generation prevention circuit according to the present invention has a constant voltage I
The output side of C falls to the ground for some reason,
Alternatively, the state when the overload occurs is a constant voltage IC
It is detected by the Zener diode connected between the input and output terminals, and the Zener diode is made conductive, and the potential on the input side of the constant voltage IC is set to the ground level or a value close to it, and the heat generation of the constant voltage IC is quickly suppressed to ensure safety. Can be secured.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an electric circuit diagram of a television device having an abnormal heat generation prevention circuit. In FIG. 1, the same parts as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

The stabilized DC voltage supply circuit 2 is connected to the secondary coil L3 of the flyback transformer 51. The stabilized DC voltage supply circuit 2 has a constant voltage IC 56.
The Zener diode ZD1 is connected between the input and output terminals of a, and the Zener diode ZD1 and the constant voltage IC are connected.
An overcurrent protection element R11 is connected in series commonly to 56a. The overcurrent protection element R11 is the same as or equivalent to a bimetal fuse or a normal fuse.

In the stabilized DC voltage supply circuit 2, the output side of the constant voltage IC 56a is short-circuited to the ground due to a short circuit between the electrodes of the output capacitor C1 for some reason, or an overload causes a constant voltage. IC56
When the output current value of a becomes excessively large, a part of the input is consumed as heat energy inside the constant voltage IC 56a in order to suppress this output current, and along with this, the secondary coil of the flyback transformer 51. Constant voltage IC 56a from L3
The current supplied to the flyback transformer 51 increases and the flyback transformer 51 generates heat. In such a state, the voltage applied between the cathode / anode of the Zener diode ZD1 exceeds the Zener voltage, the Zener diode ZD1 becomes conductive, and a sufficient current for operating the overcurrent protection element R11 is supplied to the overcurrent element R11. Flowing. The overcurrent protection element R11 shuts off the input side of the constant voltage IC 56a from the secondary coil L3 of the flyback transformer 51 by this current, and the constant voltage IC
The heat generation of 56a is prevented.

Next, the stabilized DC voltage supply circuit 3 includes a Zener diode ZD2 between the input and output terminals of the constant voltage IC 55.
Further, the cathode of the Zener diode ZD2 and the input side of the constant voltage IC 55 are connected to the power-on signal output terminal P-ON of the microcomputer 54 via the diode D1. The diodes D2 and D3 cancel the voltage drop due to the Zener diode ZD2 and the diode D1 and may be unnecessary.

In the stabilized DC voltage supply circuit 3, the output side of the constant voltage IC 55 is short-circuited to the ground for some reason, for example, the output capacitor C2 is short-circuited between the electrodes, or is overloaded and becomes a constant voltage. When the output current value of the IC 55 becomes excessive, a part of the input is consumed as heat energy inside the constant voltage IC 55 in order to suppress the output current. Along with this, the current supplied from the primary coil L1 of the flyback transformer 51 to the constant voltage IC 55 increases, and the flyback transformer 51 generates heat. If this happens, the Zener diode ZD2
The voltage applied between the cathode and the anode of the zener diode ZD1 becomes conductive and the constant voltage I
The input side of C55 falls to the ground potential. Therefore, the power-on signal output terminal P-O of the microcomputer 54
N becomes "L" level. Power-on signal output terminal P-
At the falling timing when ON becomes “L” level,
The "L" level pulse signal is supplied from the one-shot circuit 1c to the reset terminal of the latch circuit 1a via the AND circuit 1b to turn off the switching transistor Q10 and open the relay contact 58a to stop the operation of the power supply circuit 60. The heat generation of the constant voltage IC 55 is prevented.

[0017]

As described above, if the output side of the constant voltage IC having the heat generation prevention circuit falls to the ground or is overloaded for some reason, the input / output terminals of the constant voltage IC will be described. The zener diode connected between the two is made conductive, the current bypasses the constant voltage IC, the voltage between the input and output of the constant voltage IC is balanced, the constant voltage IC is protected, and further the constant voltage IC has its constant voltage on the input side. The overcurrent is interrupted by an overcurrent interrupting means that is inserted in series with the voltage IC and the Zener diode in common. Therefore, it is possible to quickly suppress heat generation in the constant voltage IC path due to overload and ensure safety.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a circuit configuration using a constant voltage IC having an abnormal heat generation prevention circuit according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a circuit using a conventional constant voltage IC.

[Explanation of symbols]

 2, 3 stabilized DC voltage supply circuit 51 flyback transformer 54 microcomputer 55, 56a constant voltage IC 58 relay circuit (power supply stopping means) L1 primary coil L2 secondary coil L3 high voltage winding R11 overcurrent protection element ( Overcurrent interruption means) ZD1, ZD2 Zener diode

Claims (1)

[Claims] 1. In a circuit for obtaining a DC power supply by a constant voltage IC, a Zener diode connected between the input and output terminals of the constant voltage IC and an input side potential of the constant voltage IC have a ground level or a value close to the ground level. An abnormal heat generation prevention circuit, comprising: an electric power supply stopping means for stopping the electric power supplied when the abnormal heat is generated.