CN104866001A

CN104866001A - Current-limiting circuit

Info

Publication number: CN104866001A
Application number: CN201510135727.5A
Authority: CN
Inventors: 史翠萍
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-03-26
Filing date: 2015-03-26
Publication date: 2015-08-26

Abstract

A current-limiting circuit comprises a sampling resistor, a filter capacitor connected with an output terminal, a current-limiting triode, a control triode and a control switch triode, wherein the base electrode of the current-limiting triode is connected with the collecting electrode of the control triode, the emitting electrode of the current-limiting triode is connected with a power supply circuit output terminal, and the collecting electrode of the current-limiting triode is connected with the output terminal; the base electrode of the control triode is connected with the power supply circuit output terminal, and the emitting electrode of the control triode is connected with a +12V power supply; the sampling resistor is connected between the power supply circuit output terminal and the +12V power supply; the emitting electrode of the control switch triode is grounded, the base electrode of the control switch triode is connected with an enable signal end, and a current-limiting resistor is connected in series between the base electrode of the control switch triode and the enable signal end; the collecting electrode of the control switch triode is connected with the base electrode of the current-limiting triode, and a divider resistor is connected in series between the collecting electrode of the control switch triode and the base electrode of the current-limiting triode; the collecting electrode of the control triode is connected with the +12V power supply, and another divider resistor is connected in series between the collecting electrode of the control triode and the +12V power supply. According to the current-limiting circuit, the current-limiting value does not fluctuate along with variation of voltage, is relatively high in precision, has the negative temperature coefficient characteristic, and is reduced along with temperature rise of the circuit, so that the electric energy is saved.

Description

Current-limiting circuit

Technical field

The application relates to a kind of current-limiting circuit, specifically a kind of for the current-limiting circuit in low-voltage power line carrier communication module.

Background technology

Existing current-limiting circuit known at present, circuit structure is complicated, and circuit component is numerous, and production cost is higher, and there is positive temperature coefficient (PTC), and cut-off current precision is low.

Current-limiting circuit in carrier module as shown in Fig. 1, current-limiting circuit effect is the maximum current consumption of the right+12V of restriction carrier module, if the current amplification factor HFE=300 of triode, restriction output current should be no more than 156mA, after circuit enters current-limit mode, triode V3 can generate heat, temperature raises, the current amplification factor HFE of triode is caused to increase, thus making output current become large, the temperature of triode V3 continues to raise, and continues to make output current become large, define positive feedback, do not reach good current limitation effect.Current-limiting circuit is also subject to the impact of supply voltage, and when supply voltage raises, cut-off current increases, and when the supply voltage decreases, cut-off current reduces, and cut-off current is unstable.And the degree of accuracy of the current amplification factor HFE of triode is lower, also can the precision of first cut-off current.

Summary of the invention

The application is for existing current-limiting circuit complex structure, and the problems such as circuit component is numerous, and production cost is higher, and there is positive temperature coefficient (PTC), and cut-off current precision is low, devise a kind of current-limiting circuit.

A kind of current-limiting circuit of the application, comprises two current sampling resistors, the filter capacitor be connected with output terminal, current limliting triode in parallel, controls triode, gauge tap triode, filter capacitor ground connection; The base stage of current limliting triode is connected with the collector controlling triode; The collector of current limliting triode is connected with output terminal; The emitter of current limliting triode is connected with power circuit output end; The base stage controlling triode is connected with power circuit output end; The emitter controlling triode is connected with+12V power supply; Two current sampling resistors in parallel are connected between power circuit output end and+12V power supply; The grounded emitter of gauge tap triode; The base stage of gauge tap triode is connected with enable signal end, is connected with current-limiting resistance therebetween; The collector of gauge tap triode is connected with the base stage of current limliting triode, is in series with divider resistance therebetween; The collector controlling triode is connected with+12V power supply, is connected with divider resistance therebetween.

Preferably, current limliting triode and control triode are PNP type triode, and gauge tap triode is NPN type triode.

Preferably, the base stage and the power circuit output end that control triode are also connected with divider resistance therebetween.

Preferably, buffer resistance is connected with between power circuit output end and output terminal.

The beneficial effect of the application is: the cut-off current of current-limiting circuit does not fluctuate with the change of voltage, cut-off current precision is higher, current-limiting circuit has the characteristic of negative temperature coefficient, along with the rising of circuit temperature, cut-off current reduces, can electric energy be saved, make circuit can not damage because of overheated simultaneously, improve the reliability of circuit.

Accompanying drawing explanation

Accompanying drawing 1 is the circuit theory diagrams of existing current-limiting circuit.

Accompanying drawing 2 is the circuit theory diagrams of the current-limiting circuit of the application.

Accompanying drawing 3 is the structured flowchart of the current-limiting circuit of the application.

Embodiment

A kind of current-limiting circuit of the application, as shown in Fig. 2 to 3, comprise two current sampling resistor R38, R39, the filter capacitor C26 be connected with output terminal, current limliting triode Q7 in parallel, control triode Q8, gauge tap triode Q9, current limliting triode Q7 and control triode Q8 is PNP type triode, and gauge tap triode Q9 is NPN type triode.

Filter capacitor C26 ground connection; The base stage of current limliting triode Q7 is connected with the collector controlling triode Q8; The collector of current limliting triode Q7 is connected with output terminal; The emitter of current limliting triode Q7 is connected with power circuit output end VCC; The base stage controlling triode Q8 is connected with power circuit output end VCC, is also connected with divider resistance R37 therebetween; The emitter controlling triode Q8 is connected with+12V power supply; Two current sampling resistors R38, R39 in parallel are connected between power circuit output end VCC and+12V power supply; The grounded emitter of gauge tap triode Q9; The base stage of gauge tap triode Q9 is connected with enable signal end, is connected with current-limiting resistance R42 therebetween; The collector of gauge tap triode Q9 is connected with the base stage of current limliting triode Q7, is in series with divider resistance R40 therebetween; The collector controlling triode Q8 is connected with+12V power supply, is connected with divider resistance R41 therebetween; Buffer resistance R36 is connected with between power circuit output end VCC and output terminal.

When the voltage at current sampling resistor R38 and R39 two ends is higher than 0.6V, control triode Q8 conducting, the voltage controlled between the collector C of triode Q8 and emitter E can be reduced to about 0.3V, divider resistance R37 is the resistance that resistance is less, when voltage between the collector C controlling triode Q8 and emitter E can be reduced to 0.3V, voltage between the collector B of current limliting triode Q7 and emitter E is also approximate reduces to 0.3V, now current limliting triode Q7 turns off, and the emitter current of current limliting triode Q7 stops.

When current-limiting resistance R42 does not work, gauge tap triode Q9 blocks the electric current of divider resistance R40 and R41, reduces quiescent dissipation, reaches energy-conservation object.

Divider resistance R40 and R41 provides base voltage for current limliting triode Q7; when the voltage drop of+12V power supply; voltage U be between the base stage of current limliting triode Q7 and emitter also can reduce; when voltage U be between the base stage and emitter of current limliting triode Q7 is lower than 0.6V; current limliting triode Q7 turns off; the emitter current of current limliting triode Q7 stops, and reaches the object of under-voltage protection.

When current-limiting circuit enters current-limit mode, the temperature of current limliting triode Q7 rises, control triode Q8 also can receive the heat that current limliting triode Q7 passes over its temperature is raised, after the temperature rising of current limliting triode Q7 and control triode Q8, voltage U be between its respective base stage and emitter reduces, cut-off current reduces, and makes current-limiting circuit have the characteristic of negative temperature coefficient.

Claims

1. a current-limiting circuit, it is characterized in that, comprise two current sampling resistors (R38, R39), the filter capacitor (C26) be connected with output terminal, current limliting triode (Q7) in parallel, control triode (Q8), gauge tap triode (Q9), filter capacitor (C26) ground connection; The base stage of current limliting triode (Q7) is connected with the collector controlling triode (Q8); The collector of current limliting triode (Q7) is connected with output terminal; The emitter of current limliting triode (Q7) is connected with power circuit output end (VCC); The base stage controlling triode (Q8) is connected with power circuit output end (VCC); The emitter controlling triode (Q8) is connected with+12V power supply; Two current sampling resistors (R38, R39) in parallel are connected between power circuit output end (VCC) and+12V power supply; The grounded emitter of gauge tap triode (Q9); The base stage of gauge tap triode (Q9) is connected with enable signal end, is connected with current-limiting resistance (R42) therebetween; The collector of gauge tap triode (Q9) is connected with the base stage of current limliting triode (Q7), is in series with divider resistance (R40) therebetween; The collector controlling triode (Q8) is connected with+12V power supply, is connected with divider resistance (R41) therebetween.

2. current-limiting circuit according to claim 1, is characterized in that, current limliting triode (Q7) and control triode (Q8) are PNP type triode, and gauge tap triode (Q9) is NPN type triode.

3. current-limiting circuit according to claim 1 and 2, is characterized in that, the base stage and the power circuit output end (VCC) that control triode (Q8) are also connected with divider resistance (R37) therebetween.

4. current-limiting circuit according to claim 1 and 2, is characterized in that, is connected with buffer resistance (R36) between power circuit output end (VCC) and output terminal.