CN111526640A

CN111526640A - LED drive circuit

Info

Publication number: CN111526640A
Application number: CN202010483214.4A
Authority: CN
Inventors: 龚飞龙
Original assignee: Ningbo Sanity Lighting Electrical Appliance Co ltd
Current assignee: Ningbo Sanity Lighting Electrical Appliance Co ltd
Priority date: 2020-06-01
Filing date: 2020-06-01
Publication date: 2020-08-11

Abstract

The invention discloses an LED drive circuit, which comprises a step-down conversion circuit for converting commercial power alternating current into first power supply voltage for output, a battery power supply for providing second power supply voltage, a drive circuit, a first LED assembly and a second LED assembly, wherein the second power supply voltage and the drive circuit are used for driving the first LED assembly, and the first power supply voltage is used for driving the second LED assembly, and the LED drive circuit is characterized in that: the LED driving circuit further includes: a forced turn-off circuit for outputting a signal to the driving circuit to turn off the driving circuit when the first supply voltage is present; and the protection circuit is used for outputting a signal to the driving circuit to enable the driving circuit to be cut off when the second power supply voltage is lower than a set value. Compared with the prior art, the invention has the advantages that: the state of the battery power supply is judged by the analog circuit, so that the driving circuit drives the LED assembly to display different state indications in different power supply states, the application design is more flexible, and the cost is reduced.

Description

LED drive circuit

Technical Field

The invention relates to a driving circuit, in particular to an LED driving circuit.

Background

The LED is a semiconductor device with sensitive characteristics and has negative temperature characteristics, so that a stable working state and protection need to be performed on the LED in an application process, a driving concept is generated, the requirement of the LED device on a driving power supply is almost strict, the LED is not similar to a common incandescent bulb, the LED can be directly connected with a 220V alternating current mains supply, and due to the limitation of the power level of the LED, a plurality of LEDs are generally required to be driven simultaneously to meet the brightness requirement, so that a special driving circuit is required to light the LED.

In the prior art, in order to prevent the emergency of sudden power failure, an emergency lamp is often arranged in a corridor. At present, an emergency driving module used in China is an independent module and is connected with a storage battery, and when the emergency driving module is used, the emergency driving module needs to be connected with an external power supply drive of an LED lamp, and then the LED lamp is connected with the emergency driving module. During normal power supply, the mains voltage directly supplies power for the LED, charges for the battery simultaneously, and when taking place the outage, the battery discharges and supplies power for the LED lamp through emergency drive module, and at this moment, the luminance of LED lamp is darker than the luminance when normally supplying power to guarantee that the illumination is normal, can not influence people's basic action.

An existing LED driving circuit, such as an LED driving circuit which realizes multiple output mode settings through a dial disclosed in chinese patent application No. 201610320640.X, includes an emergency driving LED circuit and a commercial power driving LED circuit, the emergency driving LED circuit is powered by a battery, a single-chip microcomputer detects the presence or absence of commercial power, a bidirectional thyristor is turned on or off to control the state of the emergency driving LED or the commercial power driving LED, the emergency driving LED circuit sets the output current or output power or battery capacity and battery discharge time of the LED with a BCD dial, the code of the BCD dial corresponds to a set output current value or output power value or battery capacity and battery discharge time, the BCD dial sends the corresponding code to the single-chip microcomputer, the single-chip microcomputer outputs different modulation pulses with different duty ratios according to the code of the BCD dial, and sends the modulation pulses to a DC-DC conversion circuit, the aim of multi-level dimming of the LED lamp is achieved.

Most of existing driving circuits are as shown above, and need to use a single chip microcomputer to detect voltage, which results in high cost and complex circuit.

Disclosure of Invention

The invention aims to solve the technical problem of providing the LED driving circuit which is convenient in voltage detection, simple in circuit structure and quick in response aiming at the defects of the prior art.

The technical scheme adopted by the invention for solving the technical problems is as follows: the utility model provides a LED drive circuit, includes the step-down converting circuit who converts commercial power alternating current to first supply voltage output, provides second supply voltage's battery power, drive circuit, first LED subassembly and second LED subassembly, second supply voltage and drive circuit are used for driving first LED subassembly, first supply voltage is used for driving second LED subassembly, its characterized in that: the LED driving circuit further includes:

a forced turn-off circuit for outputting a signal to the driving circuit to turn off the driving circuit when the first supply voltage is present;

and the protection circuit is used for outputting a signal to the driving circuit to enable the driving circuit to be cut off when the second power supply voltage is lower than a set value.

Preferably, the LED assembly is driven by a triode, the driving circuit includes a third triode, a collector of the third triode is connected to the first LED assembly, an emitter of the third triode is grounded, an output end of the protection circuit is connected to a base of the third triode, and the third triode is turned off when the first supply voltage exists or the second supply voltage is lower than a set value.

Preferably, in order to facilitate the automatic output of the signal to turn off the driving circuit when it is detected that the output voltage of the battery power supply exceeds a set value, the protection circuit includes a fifth transistor and a sixth transistor, the output terminal of the battery power supply is connected to the base of the fifth transistor through a zener diode, the emitter of the fifth transistor is grounded, the collector of the fifth transistor is connected to the base of the sixth transistor, the collector of the sixth transistor serves as the output terminal of the protection circuit, and the set value is the regulated voltage of the zener diode.

Preferably, in order to facilitate the control of the transistor of the driving circuit to be turned off when the mains supply is supplied, the driving circuit further comprises a second optocoupler, a collector of the phototransistor on the secondary side of the second optocoupler is connected to the output end of the battery power supply, an emitter of the phototransistor is connected to a base of the third transistor, and an output end of the forced turn-off circuit is connected to an input end of the second optocoupler and can control the turn-on or turn-off of the third transistor by controlling the turn-on or turn-off of the second optocoupler.

Preferably, in order to cut off the second optocoupler when the mains supply is provided, the forced shutdown circuit includes a fourth triode, an output terminal of the step-down conversion circuit is connected to a base of the fourth triode, and an emitter and a collector of the fourth triode are grounded and used as an output terminal of the forced shutdown circuit.

Preferably, in order to facilitate voltage division and provide a driving voltage and current signal, a seventh resistor and an eighth resistor are sequentially connected between the output end of the battery power supply and the anode of the photodiode on the primary side of the second optocoupler, and the output end of the forced turn-off circuit is connected to the common end of the seventh resistor and the eighth resistor.

Preferably, in order to maintain the voltage of one of the input ends of the second optocoupler and ensure that the driving voltage can be switched on after the mains supply fails, the LED driving circuit further includes a triggering and interlocking circuit, the triggering and interlocking circuit includes a first triode and a second triode driven by a first power supply voltage, an emitter of the first triode is grounded, a collector of the first triode is connected to a base of the second triode and a cathode of a photodiode on a primary side of the second optocoupler of the driving circuit, respectively, an output end of the battery power supply is connected to the base and an emitter of the second triode, a collector of the second triode is connected to the base of the first triode, so that the first triode and the second triode form interlocking, and an output end of the forced turn-off circuit is connected to the emitter of the second triode.

Preferably, in order to control the driving of the first transistor, the triggering and interlocking circuit further includes a first optocoupler, and the first supply voltage drives the first transistor through the first optocoupler.

Preferably, the first power supply voltage provides a driving voltage for the first optocoupler, a collector of a phototriode of the secondary side of the first optocoupler is connected to an output end of the battery power supply, and an emitter of the phototriode of the secondary side of the first optocoupler is connected to a base of the first triode, so that the first power supply voltage can drive the first triode.

Compared with the prior art, the invention has the advantages that: the forced shutdown circuit and the protection circuit are arranged to replace a single chip microcomputer, and the state of the battery power supply is judged by the analog circuit, so that the driving circuit drives the LED assembly to display different state indications in different power supply states, the application design is more flexible, and the cost is reduced.

Drawings

FIG. 1 is a functional block diagram of a driving circuit according to an embodiment of the present invention;

FIG. 2 is a circuit schematic of a driver circuit according to an embodiment of the present invention;

fig. 3 is a schematic circuit diagram of a commercial power driving status indicator lamp of the driving circuit according to the embodiment of the invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

In the following description, it is to be noted that, unless explicitly stated or limited otherwise, the term "connected" is to be understood broadly, for example, it may be a fixed connection, a detachable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Furthermore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

Referring to fig. 1 and 2, the LED driving circuit includes a step-down conversion circuit 1, a trigger and interlock circuit 2, a driving circuit 3, a forced shutdown circuit 4, a protection circuit 5, and a battery power supply 6. The mains supply input is converted by the step-down conversion circuit 1 to obtain a first power supply voltage VCC, and the output of the battery power supply 6 provides a second power supply voltage VDD. The output end (first supply voltage VCC) of the step-down conversion circuit 1 is connected to the input end of the triggering and interlocking circuit 2 and the input end of the forced shutdown circuit 3, respectively, to supply power thereto, and the output end (second supply voltage VDD) of the battery power supply 6 is connected to the input end of the triggering and interlocking circuit 2, to supply power thereto. The output of the forced shutdown circuit 3 is connected to the triggering and interlock circuit 2. The output end of the triggering and interlocking circuit 2 is connected with the input end of the driving circuit 3, the output end of the driving circuit 3 is connected to the first LED assembly 7, and the first LED assembly 7 may include N series-connected LEDs, which are LED1 and LED2 … … LEDN respectively. The output of the driving circuit 3 and the output of the battery power supply 6 are connected to both ends of the first LED assembly 7, respectively. An output terminal of the protection circuit 5 is connected to the drive circuit 3.

The triggering and interlocking circuit 2 comprises a first optocoupler U1, a first triode Q1 and a second triode Q2, the output end of the voltage reduction and conversion circuit 1 is connected to one input end (the anode of the primary side photosensitive diode) of the first optocoupler U1, and the other input end (the cathode of the primary side photosensitive diode) of the first optocoupler U1 is grounded. The voltage divider circuit can be connected between the output of first opto-coupler U1 and step-down converting circuit 1, including first resistance R1 and the second resistance R2 of establishing ties each other, the one end of first resistance R1 is connected with step-down converting circuit 1's output, the other end is connected with the one end of second resistance R2, the other end ground connection of second resistance R2, an input of first opto-coupler U1 is connected between first resistance R1 and second resistance R2, the both ends of second resistance R2 can have first electric capacity C1 in parallel. Therefore, when the output end of the buck conversion circuit 1 supplies power to the first optocoupler U1, the photodiode on the primary side of the first optocoupler U1 can be switched on and emit light, and the base of the phototriode on the secondary side of the first optocoupler U1 receives signals and is switched on to be in a saturated state.

The output end of the battery power supply 6 is connected to one of the output ends (collector of secondary photosensitive triode) of the first optocoupler U1, the other output end (emitter of secondary photosensitive triode) of the first optocoupler U1 is connected to the base of the first triode Q1, a first diode D1 and a third resistor R3 can be arranged between the output end of the first optocoupler U1 and the first triode Q1, the anode of the first diode D1 is connected with the first optocoupler U1, the cathode of the first diode D1 is connected with one end of the third resistor R3, and the other end of the third resistor R3 is connected to the first triode Q1. The emitter of the first transistor Q1 is grounded. The triggering and interlocking circuit 2 further comprises a second capacitor C2 and a fourth resistor R4, wherein the second capacitor C2 and the fourth resistor R4 are connected in parallel, and then two ends of the second capacitor C2 and two ends of the fourth resistor R4 are respectively connected to the base of the first triode Q1 and the ground.

The collector of the first transistor Q1 is connected to the base of the second transistor Q2, and the collector of the second transistor Q2 is electrically connected to the base of the first transistor Q1. The base and emitter of the second transistor Q2 are also connected to the output of the battery power supply 6, respectively. A third capacitor C3 and a fifth resistor R5 are connected between the base of the second triode Q2 and the output end of the battery power supply 6, the third capacitor C3 is connected with the fifth resistor R5 in parallel, and the fifth resistor R5 forms a base driving current-limiting resistor of the second triode Q3. A sixth resistor R6 is connected between the emitter of the second transistor Q2 and the output terminal of the battery power supply 6, and the sixth resistor R6 is a collector current-limiting resistor of the second transistor Q2.

The first triode Q1, the optional NPN triode, the second triode Q2, the optional quota PNP triode.

The driving circuit 3 includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, a second optocoupler U2, a fourth capacitor C4, an eleventh resistor R11, and a third transistor Q3. One end of the seventh resistor R7 is connected to the output end of the battery power supply 6, the other end of the seventh resistor R7 is connected to one end of the eighth resistor R8, the other end of the eighth resistor R8 is connected to one of the input ends (the positive electrode of the primary photodiode) of the second optocoupler U2, and the seventh resistor R7 and the eighth resistor R8 provide voltage and current signals for driving the second optocoupler U2. The other input end (the cathode of the primary photodiode) of the second optocoupler U2 is connected to the collector of the first transistor Q1. One end of a ninth resistor R9 is connected to the output end of the battery power supply 6, the other end of the ninth resistor R9 is connected to one end of a tenth resistor R10, the other end of the tenth resistor R10 is connected to one of the output ends (the collector of the secondary phototriac) of the second optocoupler U2, the other output end (the emitter of the secondary phototriac) of the second optocoupler U2 is connected to the base of the third triode Q3, the emitter of the third triode Q3 is grounded, the collector of the third triode Q3 is connected to one end of the first LED module 7, and the other end of the first LED module 7 is connected to the output end of the battery power supply 6. After being connected in parallel, the fourth capacitor C4 and the eleventh resistor R11 are connected between the base and the emitter of the third triode Q3 at two ends respectively.

The third transistor Q3 is optionally an NPN transistor.

The forced shutdown circuit 4 includes a twelfth resistor R12, a fifth capacitor C5, a thirteenth resistor R13, and a fourth transistor Q4. One end of the twelfth resistor R12 is connected to the output end of the buck conversion circuit 1, the other end of the twelfth resistor R12 is connected to the base of the fourth triode Q4, the emitter of the fourth triode Q4 is grounded, and after the fifth capacitor C5 and the thirteenth resistor R13 are connected in parallel, the two ends of the twelfth resistor R12 are connected to the base and the emitter of the third triode Q4 respectively. The collector of the fourth transistor Q4 is used as the output terminal of the Forced turn-off circuit 4, and outputs a VCC Forced turn-off signal (VCC Forced shutdown). The signal is input to an emitter of a second transistor Q2 of the trigger and interlock circuit 2 and an input terminal of a second optocoupler U2 of the driving circuit 3 (common terminal of the seventh resistor R7 and the eighth resistor R8).

The fourth transistor Q4 is optionally an NPN transistor.

The protection circuit 5 includes a zener diode ZD1, a fourteenth resistor R14, a fifth transistor Q5, a sixth transistor Q6, a sixth capacitor C6, a sixteenth resistor R16, and a seventeenth resistor R17. The cathode of the zener diode ZD1 is connected to the output end of the battery power supply 6, the anode of the zener diode ZD1 is connected to one end of the fourteenth resistor R14, the other end of the fourteenth resistor R14 is connected to the base of the fifth triode Q5, the emitter of the fifth triode Q5 is grounded, and the collector of the fifth triode Q5 is connected to the base of the sixth triode Q6. After the sixth capacitor C6 and the fifteenth resistor R15 are connected in parallel, both ends of the sixth capacitor C6 and both ends of the fifteenth resistor R15 are respectively connected with the base and the emitter of the fifth triode Q5. The emitter of the sixth transistor Q6 is connected to the output terminal of the battery power supply 6 through a sixteenth resistor R16 and a seventeenth resistor R17. The zener diode ZD1, the fourteenth resistor R14, the fifth triode Q5, the sixth triode Q6, and the sixth capacitor C6 provide driving signals for the fifth triode Q5, and the sixteenth resistor R16 and the seventeenth resistor R17 provide driving signals for the sixth triode Q6. The collector of the sixth transistor Q6 is used as the output terminal of the protection resistor 5 to output the low-voltage protection signal (VDD low-voltage protection) of the battery power supply 6. This signal is output to the base of the third transistor Q3 of the drive circuit 3. When the output voltage of the battery power source 6 is too low, the protection circuit 5 may control the third transistor Q3 of the driving circuit 3 to be turned off, so that the first LED assembly 7 is turned off.

Referring to fig. 3, mains power may also be used to drive the second LED assembly 8. The live line L and the zero line N of the commercial power output the first power supply voltage VCC after passing through the step-down conversion circuit 1. The step-down converting circuit 1 may be a commonly used ac/dc converting circuit, for example, the commercial ac may be rectified by the bridge circuit BD1, and then output the first power supply voltage VCC after passing through the step-down converter U3, so as to supply power to the second driving LED assembly 8 and the above-mentioned circuits.

The circuit can realize different state indication of three working states of mains supply, battery supply (emergency state) and battery low power, and the working principle is as follows:

1. when the commercial power is normally supplied, the second LED component 8 is lightened. The battery power supply 6 drives the base of the first triode Q1 through the first optocoupler U1, so that the first triode Q1 is conducted to a saturation state, the collector of the first triode Q1 momentarily pulls down the base voltage of the second triode Q2 to 0.3V, due to the PN junction effect, the second triode Q2 is conducted to a saturation state by 0.3V, and the first triode Q1 and the second triode Q2 form an interlock.

Since the output voltage VCC signal voltage of the step-down converter circuit 1 is always present, the fourth transistor Q4 of the forced turn-off circuit 4 is driven into a saturated conducting state and is continuously kept conducting since VCC is always providing energy. The collector of the fourth transistor Q4 is always connected to the emitter of the second transistor Q2, and the conduction of the fourth transistor Q4 causes the voltage of the emitter of the second transistor Q2 to be pulled down to 0.3V, at which time no current signal flows into the emitter of the second transistor Q2.

At this time, the common end of the seventh resistor R7 and the eighth resistor R8 is connected with the collector of the fourth triode Q4, and the fourth triode Q4 is kept in a conducting saturation state, so that the common end voltage of the seventh resistor R7 and the eighth resistor R8 is 0.3V, and the 0.3V cannot drive the photodiode on the primary side of the second optocoupler U2 according to the PN junction principle. Therefore, the phototriode on the secondary side of the second optocoupler U2 cannot receive the photoelectric signal and cannot be turned on, and cannot provide a current signal for the base of the third triode Q3, so that the third triode Q3 cannot be turned on, and the first LED assembly 7 cannot be turned on.

That is, in the state of the mains supply, the first LED assembly 7 is not lit, and the second LED assembly 8 is lit.

2. When the utility power fails, the second LED assembly 8 cannot be lit. The first power supply voltage VCC signal disappears, the fourth triode Q4 stops working, and since the battery power supply 6 provides the second power supply voltage VDD all the time, the first triode Q1 and the second triode Q2 are always in an interlocking state, and the signal is continuously conducted all the time. The common end of the seventh resistor R7 and the eighth resistor R8 is in a high level, current passes through a photosensitive diode on the primary side of the second optocoupler U2, a collector and an emitter of the first triode Q1 to form a loop to the ground, the photosensitive diode on the primary side of the second optocoupler U2 is conducted and emits light, and therefore the photosensitive triode on the secondary side of the second optocoupler U2 receives an optical signal and is conducted. Signals provided by the ninth resistor R9 and the tenth resistor R10 pass through the collector and the emitter of the phototransistor on the secondary side of the second optocoupler U2 to provide current signals for the base of the third triode Q3, so that the third triode Q3 is turned on, the VDD voltage passes through the first LED component 7, the emitter and the collector of the third triode Q3 to form a loop to the ground, and the first LED component 7 is turned on.

That is, in a state where the commercial power is off and the battery is supplied (emergency driving), the first LED module 7 is turned on, and the second LED module 8 is not turned on.

3. When the utility power is cut off, the second power supply voltage VDD is lower than a set value, the set value is equal to the stable voltage of the zener diode ZD1, the zener diode ZD1 is turned off, the base signal of the fifth triode Q5 disappears, the collector of the fifth triode Q5 is in a high level state, so that the sixth triode Q6 is turned on, and since the collector of the sixth triode Q5 is connected to the base of the third triode Q3, after the sixth triode Q6 is turned on, the base of the third triode Q3 is instantly pulled down to 0.3V, so that the third triode Q3 is turned off, and the first LED assembly 7 is turned off.

That is, in the state where the commercial power is cut off and the battery is supplied with low power, the first LED assembly 7 is not lit, and the second LED assembly 8 is not lit.

The power supply mode and the state of the battery power can be judged by the different lighting states of the first LED module 7 and the second LED module 8.

Claims

1. An LED drive circuit, includes step-down converting circuit (1) of converting commercial power alternating current to first supply Voltage (VCC) output, battery power (6), drive circuit (3), first LED subassembly (7) and second LED subassembly (8) that provide second supply Voltage (VDD), second supply Voltage (VDD) and drive circuit (3) are used for driving first LED subassembly (7), first supply Voltage (VCC) is used for driving second LED subassembly (8), its characterized in that: the LED driving circuit further includes:

a forced shutdown circuit (4) for outputting a signal to the drive circuit (3) to turn off the drive circuit (3) when the first supply Voltage (VCC) is present;

and a protection circuit (5) for outputting a signal to the drive circuit (3) to turn off the drive circuit (3) when the second supply Voltage (VDD) is lower than a set value.

2. The LED driving circuit according to claim 1, wherein: the driving circuit (3) comprises a third triode (Q3), the collector of the third triode (Q3) is connected to the first LED component (7), the emitter is grounded, the output end of the protection circuit (5) is connected to the base of the third triode (Q3), and the third triode (Q3) is cut off when the first supply Voltage (VCC) exists or the second supply Voltage (VDD) is lower than the set value.

3. The LED driving circuit according to claim 2, wherein: the protection circuit (5) comprises a fifth triode (Q5) and a sixth triode (Q6), the output end of the battery power supply (6) is connected to the base electrode of the fifth triode (Q5) through a voltage stabilizing diode (ZD1), the emitting electrode of the fifth triode (Q5) is grounded, the collecting electrode of the fifth triode (Q5) is connected with the base electrode of the sixth triode (Q6), the collecting electrode of the sixth triode (Q6) serves as the output end of the protection circuit (5), and the set value is the stable voltage of the voltage stabilizing diode (ZD 1).

4. The LED driving circuit according to claim 2, wherein: the driving circuit (3) further comprises a second optical coupler (U2), a collector of a phototriode on the secondary side of the second optical coupler (U2) is connected to an output end of a battery power supply (6), an emitter of the phototriode is connected to a base electrode of a third triode (Q3), an output end of the forced turn-off circuit (4) is connected to an input end of the second optical coupler (U2), and the conduction or the turn-off of the third triode (Q3) can be controlled by controlling the conduction or the turn-off of the second optical coupler (U2).

5. The LED driving circuit according to claim 4, wherein: the forced shutdown circuit (4) comprises a fourth triode (Q4), the output end of the buck conversion circuit (1) is connected to the base electrode of the fourth triode (Q4), the emitter electrode of the fourth triode (Q4) is grounded, and the collector electrode of the fourth triode serves as the output end of the forced shutdown circuit (4).

6. The LED driving circuit according to claim 4 or 5, wherein: a seventh resistor (R7) and an eighth resistor (R8) are sequentially connected between the output end of the battery power supply (6) and the anode of the primary side photosensitive diode of the second optocoupler (U2), and the output end of the forced turn-off circuit (4) is connected with the common end of the seventh resistor (R7) and the eighth resistor (R8).

7. The LED driving circuit according to claim 6, wherein: the LED driving circuit further comprises a trigger and interlock circuit (2), the trigger and interlock circuit (2) comprising a first transistor (Q1) and a second transistor (Q2) driven by a first supply Voltage (VCC), the emitter of the first triode (Q1) is grounded, the collector of the first triode (Q1) is respectively connected to the base of the second triode (Q2) and the negative electrode of the photodiode on the primary side of the second optocoupler (U2) of the driving circuit (3), the output end of the battery power supply (6) is respectively connected to the base electrode and the emitter electrode of a second triode (Q2), the collector of the second triode (Q2) is connected to the base of the first triode (Q1), thereby enabling the first transistor (Q1) and the second transistor (Q2) to form an interlock, the output end of the forced closing circuit (4) is connected to the emitter of a second triode (Q2).

8. The LED driving circuit according to claim 7, wherein: the triggering and interlocking circuit (2) further comprises a first optical coupler (U1), and the first power supply Voltage (VCC) drives a first triode (Q1) through the first optical coupler (U1).

9. The LED driving circuit according to claim 8, wherein: first supply Voltage (VCC) provides driving voltage for first opto-coupler (U1), the output of battery power (6) is connected to the collecting electrode of the phototriode on the vice limit of first opto-coupler (U1), the base of first triode (Q1) is connected to the projecting pole of the phototriode on the vice limit of first opto-coupler (U1) to make first supply Voltage (VCC) can drive first triode (Q1).