JPS6359610A - Constant voltage circuit - Google Patents

Abstract

PURPOSE:To prevent chattering by turning off a voltage switch circuit for overcurrent and causing the output signal for overcurrent to pass a timer circuit and preventing a circuit from being operated with a momentary surge current or the like. CONSTITUTION:When an overcurrent flows to a load, the potential between both ends A and B of a resistance 31 rises, and this potential acts upon the base of a transistor TR 3a as an output signal (a) to turn on the TR 3a, and charging of a capacitor 62 is started through a resistance 61 of the timer circuit. When the rise of the potential continues over a certain time, the potential of the capacitor 62 rises; and when it exceeds a certain value, a TR 7c is turned on, and the potential of an output terminal 70 falls, and an output signal (b) of the output terminal 70 becomes zero. Then, TRs 8a and 8b are turned off, and a TR 2a is turned off also, and the current of the circuit is broken. Consequently, a resistance 11 is prevented from being burnt off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant voltage circuit, and particularly to a constant voltage circuit formed on a circuit board.

[Conventional technology]

In the conventional constant voltage circuit, a DC power supply circuit 1 is connected to an output terminal 5 via a constant voltage power supply circuit 4 as shown in FIG. 3(A). Incidentally, as shown in FIG. 3(b), a constant current circuit 9 was sometimes inserted between the DC power supply circuit 1 and the constant voltage power supply circuit 4.

[Problem that the invention seeks to solve]

However, there is a drawback that the resistor 11 (see FIG. 2) of the DC power supply circuit 1 is disconnected when an overcurrent flows due to a short circuit in the load circuit or the like.

The present invention eliminates this drawback by cutting off the circuit in the event of overcurrent.

[Means for solving problems]

In the present invention, a DC power supply circuit 1 is connected to an output terminal 5 through a voltage switch circuit 2, a current detection circuit 3, and a constant voltage power supply circuit 4, and an overcurrent output signal a of the current detection circuit 3 is connected to an output terminal 5 through a timer circuit 6. A constant voltage circuit is characterized in that the signal from the holding circuit 7 is inputted to the voltage switch circuit 2 via the amplifier circuit 8 and kept turned off.

[For production]

When the load circuit is short-circuited, an overcurrent output signal a is generated from the current detection circuit 3, and when this output signal a continues for a certain period of time or more, a signal is generated from the holding circuit 7 through the timer circuit 6. turns off the voltage switch circuit 2.

〔Example〕

FIG. 2 shows a specific circuit of an embodiment of the present invention.
Parts corresponding to each part in FIG. 1 are indicated by adding numbers or Roman letters to the code of the block.

In Fig. 2, IL is the transformer of DC power supply circuit 1, and LD
is its double-wave rectifier diode, 11 is a resistor connected to its output side, and 12 is its smoothing capacitor.

2a is a switching transistor of the voltage switch circuit 2.

31 is a detection resistor of the current detection circuit 3, and 3a is a transistor that detects and amplifies the voltage across the detection resistor 31.

41 is a constant voltage power supply IC of the constant voltage power supply circuit 4.

4a and 4b are transistors for current amplification of the IC41.

The output terminal 5 is a +12 volt output terminal, 50 is its ground terminal, 51 is a -12 volt output terminal, and substantially the same circuit as the + side is connected to the output terminal 51 on one side.

The collector of the transistor 3a is the timer circuit 6 (7)
IOK ohm resistor 61 and 1μ Farad capacitor 6
2 is connected, and two 10 K ohm discharge resistors 63 and 64 are connected to its output terminal.

The holding circuit 7 consisting of a flip-flop includes a pair of transistors 7a and 7 forming a bistable multi-by-break.
b and a driving transistor 7c connected in parallel thereto,
7d, and the resistors 63 and 64 are connected to the base of the driving transistor 7C. The output terminal 70 of the transistor 7a is connected via a line 71 to the transistors 8a, 8b of the amplifier circuit 8. transistor 8b
The output terminal of the transistor 2a is connected to the base of the transistor 2a.

A reset circuit 10 is provided at the base of the driving transistor 7d.
The output terminal of the transistor 10a is connected.

101 is an ohm resistor at 100 of the reset circuit 10, and 1
02 is a 10μ Farad capacitor, and these resistors 10
1. The capacitor 102 constitutes a timer circuit with a long time constant. The output terminal of this timer circuit is connected via a resistor 106 to the base of transistor 10a. Note that the resistance is 10
7 is a discharge resistor. 103, 104, and 105 are series resistors for the initial drive of the reset circuit 10;
3.104 is connected to the collector of the transistor 10a, and the resistor 104 and 105 is connected to the base of the driving transistor 7d.

Next, the operation of this device will be explained.

When power is applied, first the resistor 1o3 of the reset circuit 10
, 1o4.105, and the driving transistor 7
d is turned on, and the collector potential of the transistor 7b constituting the flip-flop becomes 0 and the collector potential of the transistor 7a becomes 1. As a result, the output signal at the output terminal 70 becomes 1, and this 1 signal is sent to the transistor 8a through the line 71. As a result, transistors 8a and 8b are turned on, transistor 2a is turned on, and transistor 2 is turned on by resistor 11 of current power supply circuit 1.
a, resistance 31. Power transistor 4 of constant voltage power supply circuit 4
A current flows to the output terminal 5 through b. After this, the resistor 101 of the reset circuit 10. A timer circuit consisting of a capacitor 102 operates, and when the capacitor 102 is charged, the transistor 10a is turned on and the output voltage at its collector becomes O, and the driving transistor 7d is kept in an off state.

When an overcurrent flows through the load, the potential at both ends A and B of the resistor 31 increases, and this potential is applied to the transistor 3a as the output signal a.
The transistor 3a is turned on, and charging of the capacitor 62 is started through the resistor 61 of the timer circuit 6. However, unless this potential rise is sustained, the discharging rate due to the resistors 63 and 64 will be faster than the charging rate. Therefore, transistor 7c is not turned on. When the potential rise continues for a period of time or longer, the potential of the capacitor 62 increases,
When the value of
becomes.

As a result, transistors 8a and 8b are turned off, transistor 2a is also turned off, and the current in the circuit is cut off. Therefore, burning out of the resistor 11 can be prevented.

Even in this case, since the capacitor 102 of the timer circuit of the reset circuit IO remains charged, the transistor 10a remains on as described above, and the driving transistor d remains off, so the off state of the switching transistor 2a continues. .

When the power is turned off and the power is applied again after the capacitor 102 of the timer circuit is discharged, the reset circuit 10 is activated as described above.
resistance 103. A current flows to 10=1,105, and a current flows to the output terminal 5 in the same manner.

As described above, damage to the DC power supply circuit 1 is prevented.

〔Effect of the invention〕

As described above, according to the present invention, the voltage switch circuit 2 is turned off in the event of overcurrent, thereby preventing damage to the DC power supply circuit 1. However, since the output signal a at the time of overcurrent is passed through the timer circuit 6, It does not operate under normal surge currents and prevents chattering.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an outline of the present invention, FIG. 2 is a circuit diagram of one embodiment thereof, and FIG. 3 (A) (+7) is a block diagram showing two examples of conventional circuits. ■・・・DC' modified cooling circuit, 2... Voltage switch circuit, 3... Current detection circuit, 4...
... Constant voltage power supply circuit, 5 ... Output terminal, a.
...Signal, 6...Timer circuit, 7...
...Holding circuit, b...Signal, 8...
Amplification circuit. Answer 1 orchid

Claims (1)

[Claims] The DC power supply circuit is connected to the output terminal via a voltage switch circuit, a current detection circuit, and a constant voltage power supply circuit, and the overcurrent output signal of the current detection circuit is input to the holding circuit via the timer circuit. A constant voltage circuit characterized in that a signal is input to the voltage switch circuit through an amplifier circuit and held in the off state.