CN106546804A - A kind of transistor over-current detection circuit - Google Patents

Abstract

The invention discloses a transistor overcurrent detection circuit, which relates to the technical field of overcurrent detection, including single-phase power lines (L, N), circuit breakers (QF), fuses (FU), contactors (KM), intermediate relays ( KA), current transformer (TA), step-down transformer (T), rectifier bridge (UR1), rectifier bridge (UR2), transistor (VT1), transistor (VT2), three-terminal voltage regulator 7812, resistor, capacitor, components such as light emitting diodes. The transistor overcurrent detection circuit of the invention has simple structure and low cost; the circuit can automatically cut off the power supply when the user uses electricity for overcurrent or the power supply line has a short circuit fault.

Description

A Transistor Overcurrent Detection Circuit

technical field

The invention relates to the technical field of overcurrent detection, in particular to a transistor overcurrent detection circuit.

Background technique

Overcurrent protection is a protection method that makes the protection device operate when the current exceeds a predetermined maximum value. When the current flowing through the protected element exceeds a preset value, the protection device starts and uses a time limit to ensure the selection of the action. To trip the circuit breaker or give an alarm signal. When a phase-to-phase short circuit fault occurs in the power grid, the current will suddenly increase and the voltage will suddenly drop. The overcurrent protection is to set the operating current of the current relay according to the requirements of line selectivity. When the fault current in the line reaches the operating value of the current relay, The action of the current relay selectively cuts off the fault line according to the selective requirements of the protection device.

Contents of the invention

The present invention provides a transistor overcurrent detection circuit in order to automatically cut off the power supply circuit when the user uses overcurrent or the power supply line has a short circuit fault.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A transistor overcurrent detection circuit, comprising single-phase power lines (L, N), the single-phase power lines (L, N) sequentially through the circuit breaker (QF), fuse (FU), contactor (KM) The main contact supplies power to the load, and the coil of the contactor (KM) is connected in series with the normally closed contact of the intermediate relay (KA) and then connected in parallel between the single-phase power lines (L, N); the single-phase power lines (L, N) Both ends are connected to the primary side of the transformer (T), the secondary side of the transformer (T) is rectified by the rectifier bridge (UR2), filtered by the filter capacitor (C2), and connected to the input end of the three-terminal voltage regulator 7812, the three-terminal voltage regulator The ground terminal of the 7812 is connected to the ground, and the output terminal of the three-terminal voltage regulator 7812 outputs 12V DC; the primary side of the current transformer (TA) is connected in series to the single-phase power line (L), and the secondary side of the current transformer (TA) passes through The rectifier bridge (UR1) rectifies and filters through the filter capacitor (C1), the resistor (R1) is connected in parallel to both ends of the filter capacitor (C1), the base of the transistor (VT1) is connected to the resistor (R1), and the emitter of the transistor (VT1) It is connected to the base of the transistor (VT2), the collector of the transistor (VT1) is connected to the collector of the transistor (VT2), one end of the coil of the intermediate relay (KA) is connected to the collector of the transistor (VT2), and the other end is connected to the 12V DC connected.

Further, the transformer (T) is a step-down transformer.

Further, the turns ratio between the primary side and the secondary side of the transformer (T) is 18:1.

Further, a resistor (R2) is connected in series with the light emitting diode (VD1) and then connected in parallel at both ends of the coil of the intermediate relay (KA).

Further, the normally open contact of the intermediate relay (KA) is connected in series with the button (SB) and then connected in parallel between the collector and the emitter of the transistor (VT2).

Further, a resistor (R3) is connected in series with the light emitting diode (VD3) and then connected in parallel between the output terminal of the three-terminal voltage regulator 7812 and the ground.

Further, a diode (VD2) is connected between the output terminal and the input terminal of the three-terminal voltage regulator 7812 .

Further, the output terminal of the three-terminal regulator 7812 is connected in parallel with an output filter capacitor (C3).

Beneficial effects of the present invention: a transistor overcurrent detection circuit, the overcurrent detection circuit is composed of transistors, contactors, intermediate relays, current transformers, step-down transformers, voltage stabilizers, rectifier bridges, filter capacitors and other components, the circuit structure Simple and low cost; the circuit can automatically cut off the power supply when the user's power consumption is overcurrent or the power supply line is short-circuited.

Description of drawings

FIG. 1 is a schematic diagram of the overcurrent detection circuit of the present invention.

detailed description

In order to make the technical means, creative features, goals and effects achieved by the present invention easy to understand, the present invention will be further described below in conjunction with specific illustrations.

In specific implementation, in conjunction with Figure 1, a transistor overcurrent detection circuit, including single-phase power lines (L, N), circuit breaker (QF), fuse (FU), contactor (KM), intermediate relay (KA) , current transformer (TA), step-down transformer (T), rectifier bridge (UR1), rectifier bridge (UR2), transistor (VT1), transistor (VT2), three-terminal voltage regulator 7812. The single-phase power lines (L, N) supply power to the load through the main contacts of the circuit breaker (QF), fuse (FU), and contactor (KM) in sequence. The coil of the contactor (KM) is connected in series with the normally closed contact of the intermediate relay (KA) and then connected in parallel between the single-phase power lines (L, N). The two ends of the single-phase power line (L, N) are connected to the primary side of the transformer (T), the secondary side of the transformer (T) is rectified by the rectifier bridge (UR2), filtered by the filter capacitor (C2), and the The input terminal is connected, the ground terminal of the three-terminal voltage regulator 7812 is connected to the ground, and the output terminal of the three-terminal voltage regulator 7812 outputs 12V direct current. The transformer (T) is a step-down transformer, and the turns ratio of the primary side to the secondary side of the step-down transformer is 18:1. The primary side of the current transformer (TA) is connected in series on the single-phase power line (L), the secondary side of the current transformer (TA) is rectified by the rectifier bridge (UR1), filtered by the filter capacitor (C1), and the resistor (R1) is connected in parallel Both ends of the filter capacitor (C1), the base of the transistor (VT1) is connected to the resistor (R1), the emitter of the transistor (VT1) is connected to the base of the transistor (VT2), and the collector of the transistor (VT1) is connected to the transistor (VT2) ) is connected to the collector, one end of the coil of the intermediate relay (KA) is connected to the collector of the transistor (VT2), and the other end is connected to 12V DC. A resistor (R2) is connected in series with the light-emitting diode (VD1) and then connected in parallel at both ends of the coil of the intermediate relay (KA). The normally open contact with the intermediate relay (KA) is connected in series with the button (SB) and then connected in parallel between the collector and emitter of the transistor (VT2). A resistor (R3) is connected in series with the light-emitting diode (VD3) and then connected in parallel between the output terminal of the three-terminal voltage regulator 7812 and the ground. A diode ( VD2 ) is connected between the output terminal and the input terminal of the three-terminal regulator 7812 . The output terminal of the three-terminal regulator 7812 is connected in parallel with an output filter capacitor (C3).

When working specifically, turn on the circuit breaker (QF), the coil of the contactor (KM) in the main circuit is energized, the main contact of the contactor (KM) is closed, and the single-phase AC power supply supplies power to the load. If the power consumption of the user's power supply does not exceed the predetermined value of the current, the step-down transformer (T) converts 220V AC into 12V AC, which is rectified by the rectifier bridge (UR2), filtered by the filter capacitor (C2), and then passed through the three-terminal voltage stabilizer The 7812 is stabilized into 12V DC. On the one hand, the 12V DC powers the resistor (R3) and the light-emitting diode (VD2). The light-emitting diode (VD2) lights up to indicate that the user is using electricity normally; ), LED (VD1) power supply. When the user uses electricity normally, the resistor (R1) is a voltage divider potentiometer, and the resistor at the lower end divides the voltage lower, making the transistor (VT1) and transistor (VT2) non-conductive, the coil of the intermediate relay (KA) loses power, and the light-emitting diode (VD1) does not emit light.

When the user connects a high-power electrical appliance or a short-circuit fault occurs in the line, the current in the main circuit increases a lot, and the current flowing through the primary side of the current transformer (TA) in the detection circuit increases sharply, and the current transformer (TA) ) The current induced by the secondary side also increases. After being rectified by the rectifier bridge (UR2) and filtered by the filter capacitor (C1), the voltage division of the lower end of the resistor (R1) increases. When the base voltage of the transistor (VT1) exceeds 1.4V , the transistor (VT1) and transistor (VT2) are turned on, the coil of the intermediate relay (KA) is energized, and the normally closed contact of the intermediate relay (KA) is disconnected, so that the coil of the contactor (KM) is de-energized, and the main contactor (KM) The contact is disconnected, cutting off the single-phase power supply to the load. At the same time, the normally open contact of the intermediate relay (KA) is closed, the 12V direct current continuously supplies power to the coil of the intermediate relay (KA), and the light-emitting diode (VD1) emits light to remind the user of excessive power consumption or line failure. Only when the power consumption is reduced or the button (SB) is pressed, the coil of the intermediate relay (KA) is de-energized, and the normally closed contact of the intermediate relay (KA) is reset, the coil of the contactor (KM) can be re-energized, so that the main The contact is closed, and the single-phase power supply is connected to supply power to the user's load.

The transistor overcurrent detection circuit of the present invention is composed of transistors, contactors, intermediate relays, current transformers, step-down transformers, voltage stabilizers, rectifier bridges, filter capacitors and other components, and the circuit structure is simple and the cost is low; The circuit can automatically cut off the power supply when the user's electricity is over-current or the power supply line is short-circuited.

Claims (8)

1. a kind of transistor over-current detection circuit, including single phase poaer supply line (L, N), the single phase poaer supply line (L, N) are passed sequentially through Chopper (QF), fuse (FU), the main contacts of catalyst (KM) are load supplying, it is characterised in that：The line of catalyst (KM) Circle is connected in parallel between single phase poaer supply line (L, N) after being connected with the normally-closed contact of auxiliary reclay (KA)；Single phase poaer supply line (L, N) two End is connected with transformator (T) former limit, and transformator (T) secondary is filtered by filter capacitor (C2) through rectifier bridge (UR2) rectification, It is connected with the input of three terminal regulator 7812, the earth terminal of three terminal regulator 7812 is connected to the ground, three terminal regulator 7812 Outfan exports 12V unidirectional currents；Current transformer (TA) former limit is serially connected on single phase poaer supply line (L), and current transformer (TA) is secondary While through rectifier bridge (UR1) rectification, being filtered by filter capacitor (C1), resistance (R1) is connected in parallel on filter capacitor (C1) two ends, brilliant The base stage of body pipe (VT1) is connected with resistance (R1), and the emitter stage of transistor (VT1) is connected with the base stage of transistor (VT2), crystal The colelctor electrode of pipe (VT1) is connected with the colelctor electrode of transistor (VT2), coil one end of auxiliary reclay (KA) and transistor crystal Pipe (VT2) colelctor electrode is connected, and the other end is electrically connected with 12V direct currents.

2. according to a kind of transistor over-current detection circuit described in claim 1, it is characterised in that：The transformator (T) is drop Pressure transformer.

3. according to a kind of transistor over-current detection circuit described in claim 2, it is characterised in that：Transformator (T) former limit Turn ratio with secondary is 18:1.

4. according to a kind of transistor over-current detection circuit described in claim 1, it is characterised in that：There is resistance (R2) with luminous two The coil two ends of auxiliary reclay (KA) are connected in parallel on after pole pipe (VD1) series connection.

5. according to a kind of transistor over-current detection circuit described in claim 1, it is characterised in that：There is auxiliary reclay (KA) Normally opened contact is connected in parallel on after being connected with button (SB) between the colelctor electrode and emitter stage of transistor (VT2).

6. according to a kind of transistor over-current detection circuit described in claim 1, it is characterised in that：There is resistance (R3) with luminous two It is connected in parallel between 7812 outfan of three terminal regulator and ground after pole pipe (VD3) series connection.

7. according to a kind of transistor over-current detection circuit described in claim 1, it is characterised in that：The three terminal regulator 7812 Outfan and input between be connected with diode (VD2).

8. according to a kind of transistor over-current detection circuit described in claim 1, it is characterised in that：The three terminal regulator 7812 Outfan be parallel with output filter capacitor (C3).