KR910002763Y1 - Over current protective circuit - Google Patents

Abstract

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Description

On. OFF-control overcurrent protection circuit

1 is a conventional circuit diagram.

2 is a circuit diagram of the present invention.

* Explanation of symbols for main parts of the drawings

R1-R13: Resistor Q1, Q4: PNP type transistor

Q2, Q3, Q5, Q6: NPN transistor ZD: Zener diode

C1, C2: Capacitor

The present invention relates to a circuit protection according to an overcurrent input in power supply of a system, and more particularly to an overcurrent protection circuit that can be controlled on and off.

In general, the power supply circuit provides a good power supply for the electronic equipment, but when an error occurs on the power supply side or the load side, the protection of the entire system should be considered in some way.

At this time, the protection circuit requires various performances, but by installing the protection circuit, the performance of the electronic equipment should not be degraded. When an abnormality such as a load short-circuit or an overload occurs, respond before the circuit element is destroyed or malfunction in foreign noise. You won't do it. In addition, there are two types of protection circuits: a clamp type that continues as it is once a protection operation occurs and an automatic return type that automatically returns to normal operation when the cause is eliminated even if a protection operation occurs once.

As described above, many circuits for overcurrent protection have been developed, and a conventional technology is described below using satellite broadcasting receiver as an example.

Satellite broadcast receivers can be used externally by connecting a part of the internal secondary power supply to the terminal, which is used for switching signal lines.

However, in this case, if the external power is overloaded or short-circuited, the circuit or power supply inside the satellite broadcasting receiver may be fatally affected. Therefore, an overload protection circuit is required. FIG. 1 shows an example of such an overcurrent protection circuit. The transistor is connected to the input terminal through the resistor R1 and the emitter is connected to the output terminal, and through the resistor R1. An emitter and a base are connected and a collector is grounded through a resistor R2, and a base is connected through a resistor R3 with a collector of the transistor Q1, and a collector is connected to the transistor Q2. A transistor Q3 connected to the base of the transistor, a resistor R4 connected between the emitter of the transistor Q2 and the collector of the transistor Q3, a cathode connected to the resistor R4, and an anode grounded. Zener diode (ZD).

Referring to the operation process based on the above configuration will be as follows.

When power is supplied to the input terminal Vin, the current flowing to the load is substantially equal to the current I flowing through the resistor R1. In FIG. 1, the base-emitter voltage VBE of the transistor Q1 (approximately When the voltage VR1 = I-R1 applied to the resistor R1 is smaller than 0.7 volts, the transistor Q1 is turned off.

Therefore, the transistor Q3 is also turned off because the base of the transistor 03 goes low. Therefore, the emitter voltage of the transistor Q2 connected to the output terminal Vout is equal to the base-emitter voltage VBE2 (about 0.7 volts) of the transistor Q2 at the constant voltage V2 of the zener diode ZD. It will be subtracted. At this time, if it is assumed that overcurrent flows to the input terminal Vin, the voltage applied to the resistor R1 becomes larger than the base-emitter voltage VBE1 of the transistor Q1 as shown in Equation (1) below.

I R1> VBE1... … … … … … … … … … … … … … … … … … … … … … … … (One)

Therefore, the transistor Q1 is " on " and at the same time supply power is bypassed through the transistor Q1, and a supply power of "high" level is applied to the base of the transistor Q3 through the resistor R3 so that the Transistor Q3 is " turned on ". Therefore, since the value of the constant voltage Vz across the zener diode ZD becomes the conduction voltage (0.2 volt) of the transistor Q3, the output is turned off and the current is limited.

However, when the above output is turned off, the output current I becomes almost zero, so that the voltage across the resistor R1 becomes smaller than the base-emitter-to-emitter voltage VBE1 of the transistor Q1.

Therefore, the transistor Q2 is turned on so that the output appears and the transistor Q1 is turned off. The above-described processes are repeated. In practice, the switching operation is not repeated, but is operated at the on / off interface of the transistor. Is represented by a specific value. That is, since the current continues to flow even when the output is shorted, it does not become a reliable current cutoff, thereby affecting the external circuit as well as the internal circuit of the receiver (inside the set) and causing a failure of the current limiting circuit.

Accordingly, an object of the present invention is to provide an on / off controllable overcurrent or a circuit that can protect an external circuit and a receiver by reliably blocking current under an overload condition.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

2 is a circuit diagram according to the present invention, in which an emitter is transferred to a power input terminal Vin through a resistor R6, and a base Q4 and a transistor connected to an input terminal which is the power source through a resistor R7. A current limiting circuit 100 consisting of a resistor R8 connected between the base of Q4 and the node point a, and the base connected to a power on / off control signal input terminal Sc through a resistor R12; A power supply on / off control circuit 200 comprising a transistor Q6 connected to the node point b and an emitter grounded and a resistor R13 connected between the base and the ground of the transistor Q6; The base is connected to the node point (d), the collector is connected to the node point (a), the emitter is connected to the transistor (Q5) connected to the node point (b), and the resistor (R10) connected between the node points (c) and (d). ) And a resistor (R11) connected between the node point (d) and ground to detect current from the current limiting circuit (100). A current blocking unit 300 for blocking current transmission in the event of overcurrent and a resistor R9 and a capacitor C1 connected in parallel between the node points a and b to set an instant overload time And a time setting section 400, a node point c (Vout), and a capacitor C2 connected between the node point c and ground.

Referring to the present invention in detail based on the above-described configuration. In FIG. 2, when the on / off control signal Sr is in the "low" state, the transistor Q6 is "turned off" because the base is in the "low" level state, so that the transistor Q4 is independent of the state of the transistor Q5. The base is " high " level and " turned off ". Therefore, no output comes out.

In this state, however, when the on / off control signal Sc becomes "high", when the transistor Q6 is "turned on", the collimator potential is momentarily lowered to about 0.2 volts. Initial current flows.

As a result, the transistor Q4 flows from the emitter to the base so that the transistor Q1 is turned on and the output is generated, thereby increasing the base potential of the transistor Q5, thereby turning on the transistor Q5.

That is, the collector potential of the transistor Q5 is the collector emitter voltage Vce6 (on) (about 0.2 volt) of the transistor Q6 and the collector emitter voltage Vce5 (on) of the transistor Q5 ( About 0.2 volts), which is about 0.4 volts, and thus the transistor Q4 remains "on" so that output is continuously generated. That is, it can be seen that the normal output is maintained unless the on / off control signal Sc is "high" when it is not overloaded.

Assuming that the output terminal is overloaded in this state, the current I flowing through the resistor R6 increases when the overload is overloaded, so that the potential of the node point c is equal to the transistor Q4 as shown in Equation 2 below. ) Becomes smaller than the base potential of.

Vin-I-R1-VBEQI <VBQ4... … … … … … … … … … … … … … … … … … … … … (2)

(At this time, since the value of the resistor R6 is determined according to the current level to cut off, it can be seen that the resistor R6 is used as an element for determining the output cutoff level.)

Then, the transistor Q4 is turned off and at the same time the transistor Q5 is also turned off as the base potential of the transistor Q5 is lowered to reach the turn-on state as the potential of the node point c is lowered. The base potential of Q4) is further increased so that the transistor Q4 remains in the " off " state so that a complete current blocking is achieved. At the same time, when the capacitive load is connected, the initial current must be large, so that the momentary overload will continue to output when the load returns normally to accommodate this.

In addition, the time at which the momentary overload is possible is determined by the time constants of the resistor R9 and the capacitor Cl.

Herein, the operation of the capacitor Cl will be described in more detail. When the transistor Q5 is turned off during overload, the voltage across the capacitor C1 is increased while being charged with the time constant as shown in Equation 3 below. It is

R9, C1... … … … … … … … … … … … … … … … … … … … … … … … … … … (3)

If the overload is only applied for a shorter time than the time constant and then recovers to normal, the base voltage of the transistor Q1 is not increased enough to turn off the transistor Q1, and thus the output returns to normal. .

Therefore, as described above, once the cutoff state, the current is not supplied even when the load returns to normal, so a perfect current blocking effect can be expected.

In order to restore the cut-off state to the normal output state, the circuit power supply of the present invention can be turned off and on again, or the on / off control circuit signal SC must be turned "low" and then changed back to "high" state. Do. By operating as described above, it is possible to completely block the current of the output stage in case of overload, thereby protecting the circuit in case of overcurrent.

Claims (1)

In an overcurrent protection circuit of a power supply circuit, a current limiting circuit 100 that determines a current interruption level to operate as a power transmission unit, and an on to control operation of the current limiting circuit 100 according to a state of a power on / off control signal. A current blocking circuit 300 which detects a current from the on / off control circuit 200 and the current limiting circuit 100 and cuts off the current transmission of the current limiting circuit 100 when overloading for a predetermined time or more according to a current blocking level. And an instantaneous overload time setting unit 400 for determining a time constant for preventing a current interruption during an instantaneous overload.