阅读说明：本技术 一种应急灯驱动电路 (Emergency lamp drive circuit ) 是由 夏虎 刘桂芝 王冬峰 赵寿全 于 2019-09-17 设计创作，主要内容包括：本发明公开了一种应急灯驱动电路,包括电源、高压开关电源驱动电路、低压开关电源驱动电路、功率管N1、功率管N2、二极管D1、二极管D2、二极管D3、二极管D4、二极管D5、LED灯串、电容C1、地线1、地线2和变压器,所述变压器包括线圈线圈L1、线圈L2和线圈L3,本电路中仅有一个LED灯串,LED灯串中的所有灯珠都一直处于工作状态,利用率为100％,可以减少应急灯电路中灯珠的个数,节省应急灯电路的成本,通常应急灯电路中的驱动电路板和LED灯珠光源板是2块独立的电路板,通过电线连接,本发明的LED灯珠光源板与驱动电路板之间只有2根电线,而市场上通用的LED灯珠光源板也只有2根电线,所以市场上通用的LED灯珠光源板可以与本发明应急灯电路连接使用。(The invention discloses an emergency lamp driving circuit, which comprises a power supply, a high-voltage switching power supply driving circuit, a low-voltage switching power supply driving circuit, a power tube N1, a power tube N2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, LED lamp strings, a capacitor C1, a ground wire 1, a ground wire 2 and a transformer, wherein the transformer comprises a coil L1, a coil L2 and a coil L3, the circuit is only provided with one LED lamp string, all lamp beads in the LED lamp string are always in a working state, the utilization rate is 100 percent, the number of the lamp beads in the emergency lamp circuit can be reduced, the cost of the emergency lamp circuit is saved, the driving circuit board and the LED lamp bead light source board in the emergency lamp circuit are 2 independent circuit boards, the LED lamp bead light source board and the driving circuit board are connected through wires, only 2 wires are arranged between the LED lamp bead light source board and the driving circuit board, and the general LED light, therefore, the LED lamp bead light source board which is universal in the market can be connected with the emergency lamp circuit for use.)

1. An emergency lamp driving circuit, characterized in that: the LED lamp comprises a power supply, a high-voltage switching power supply driving circuit, a low-voltage switching power supply driving circuit, a power tube N1, a power tube N2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, an LED lamp string, a capacitor C1, a ground wire 1, a ground wire 2 and a transformer, wherein the transformer comprises a coil L1, a coil L2 and a coil L3;

the power supply end VCC of the high-voltage switching power supply driving circuit is connected with a positive power supply end, the ground wire end of the high-voltage switching power supply driving circuit is connected with an electric wire 2, the GATE2 end of the high-voltage switching power supply driving circuit is connected with the grid electrode of a power tube N2, the CS2 end of the high-voltage switching power supply driving circuit is connected with the ground wire 2 through a resistor R2, the drain electrode of the power tube N2 is connected with the positive power supply end, the source electrode of the power tube N2 is connected with the ground wire 2, the diode D5 is a parasitic diode of the power tube N2, the anode of the diode D4 is connected with the ground wire 2, the cathode of the diode D4 is connected with the cathode of the diode D1, the anode of the diode D1 is connected with the ground wire 1, the different-name end of the coil L2 is connected with the cathode of the diodes D1 and D48, the same-name end of the coil L2 is connected with the anode of the LED;

the negative pole of the battery is connected to a ground wire 1, the power supply end VDD of the low-voltage switching power supply driving circuit is connected with the positive pole of the battery, the ground wire of the low-voltage switching power supply driving circuit is connected with the ground wire 1, the control end of the low-voltage switching power supply driving circuit is connected with an external power supply power failure signal, the GATE1 end of the low-voltage switching power supply driving circuit is connected with the grid electrode of a power tube N1, the FB1 end of the low-voltage switching power supply driving circuit is connected with the ground wire 1 through a resistor R1, the source electrode of the power tube N1 is connected with the ground wire 1, the diode D2 is a parasitic diode of the power tube N1, the dotted terminal of the coil L1 is connected with the positive pole of the battery, the dotted terminal of the coil L1 is connected with the drain electrode of the power tube N1, the dotted terminal of the coil L3 is connected with the ground wire 1, the dotted terminal of the coil L.

2. An emergency lamp driving circuit as claimed in claim 1, wherein: the high-voltage switching power supply driving circuit is an LED constant current driving control circuit.

3. An emergency lamp driving circuit as claimed in claim 2, wherein: the chip type of the high-voltage switching power supply driving circuit is HV 9910.

4. An emergency lamp driving circuit as claimed in claim 1, wherein: the chip model of the low-voltage switching power supply driving circuit is LN 2266.

Technical Field

The invention relates to the field of emergency lamp circuits, in particular to an emergency lamp driving circuit.

Background

In many applications, emergency lights are used. The emergency lamp has the function that when the emergency lamp is normally powered, the electric energy provided by the power supply lights the light source for illumination, and simultaneously charges a battery in the emergency lamp; when a power supply is cut off due to a fire or other unpredictable disaster, a battery in the emergency lamp provides electric energy to light the light source, so that emergency illumination is provided. The emergency lamp can be applied to a residence which is frequently in power failure, and when power is off, a battery in the emergency lamp provides electric energy to light a light source, so that short-time illumination is provided for residents;

the existing emergency lamp circuit can be shown in fig. 6, the high-voltage switching power supply driving circuit is an LED constant current driving control circuit, the LED current is adjusted by adjusting the on duty ratio of a power tube N2, so that the LED current is kept constant, the power supply end VIN of the high-voltage switching power supply driving circuit is connected with the positive end of a power source VDC, the ground wire of the high-voltage switching power supply driving circuit is a ground wire 2, the GATE end of the high-voltage switching power supply driving circuit is connected with the GATE of a power tube N2, the LED light string is formed by connecting an LED light string 1, an LED light string 2 and an LED light string 3 in series, the negative electrode of the LED light string 3 is connected with the ground wire 1, one end of an inductor L1 is connected with the ground wire 2, the other end of the inductor L1 is connected with the positive electrode of the LED light string 1, the positive electrode of a diode D2 is connected with the negative electrode of the LED light string 1, the negative electrode of a diode D483, the power supply end VDD of the charge pump is connected with the anode of the battery, the ground wire of the charge pump is the ground wire 1, and the ground wire 1 is simultaneously connected with the cathode of the battery. The control end of the charge pump is connected with a power supply power failure signal, and the GATE1 end of the charge pump is connected with the grid electrode of the power tube N1.

The working principle of the existing emergency lamp circuit when charging the battery is described as follows:

when the power supply supplies power normally, the high-voltage switching power supply driving circuit works normally, the GATE2 end of the high-voltage switching power supply driving circuit is used for controlling the working state of the power tube N2 and adjusting the duty ratio of the high-voltage switching power supply to enable the current passing through the LED lamp string to be constant, the resistor R2 is used for sampling the current, and the current passing through the LED lamp string at the moment is detected; when the power supply VDC is cut off, the high voltage switching power supply driving circuit stops operating because there is no power source, the voltage at the GATE2 terminal of the high voltage switching power supply driving circuit is 0 with respect to the ground line 2, and the power tube N2 is turned off.

When the power supply VDC supplies power normally, the power supply power failure signal is invalid, the charge pump circuit does not work, the voltage of the end of the charge pump GATE1 is 0 relative to the ground wire 1, and the power tube N1 is disconnected. When the power supply VDC is powered off, a power supply power failure signal is triggered, the charge pump circuit works, the voltage at the end of the charge pump GATE1 is at a high level relative to the ground wire 1, and the power tube N1 is conducted.

When the power VDC supplies power normally, the high-voltage switch power supply driving circuit works normally; the charge pump circuit is not operated and the power tube N1 is turned off. The emergency lamp circuit comprises 2 working states shown in fig. 2 and 3 according to the working state of the power tube N2.

As shown in fig. 7, when the power source VDC supplies power normally and the signal at the GATE2 of the high voltage switching power supply driving circuit is at a high level with respect to the ground 2, the power transistor N2 is turned on, and the current output by the power source VDC flows through the power transistor N2 and the inductor L2, and then flows through the LED string simultaneously. At this time, the current of the inductor L1 increases linearly, and the inductor L1 stores energy. The current flowing through LED string 1 flows partly through LED string 2 and LED string 3, and the rest flows to the positive electrode of the battery through diode D2. At this time, the current flowing to the positive electrode of the battery through the diode D2 charges the battery.

As shown in fig. 8, when the power source VDC is normally powered and the signal at the GATE2 terminal of the high voltage switching power supply driving circuit is at a low level with respect to the ground line 2, the power transistor N2 is turned off, and at this time, the inductor L1 discharges energy, and the current passing through the inductor L1 linearly decreases. The current through the inductor flows through the LED string and returns to inductor L1 through diode D1. The current flowing through the LED string 1, a part of which flows through the LED string 2 and the LED string 3, flows to the positive electrode of the battery through the diode D2, and at this time, the battery is charged by the current flowing to the positive electrode of the battery through the diode D2.

As shown in fig. 9, when the power source VDC is powered off, the power transistor N2 is kept off when the signal at the GATE2 terminal of the high-voltage switching power supply driving circuit is kept at a low level with respect to the ground line 2, and at the same time, when the power source is powered off, the power source power failure signal is triggered, the charge pump starts to operate, so that the GATE1 terminal becomes a high level with respect to the ground line 1, and the power transistor N1 becomes conductive from off. And discharging the battery, wherein the battery discharging current flows out from the positive electrode of the battery, flows to the positive electrode of the LED lamp string 3 after passing through the power tube, and returns to the negative electrode of the battery after passing through the LED lamp string 3. At this time, no current flows through the LED string 1 and the LED string 2.

The above structure has the following problems:

because the power VDC is usually a high voltage power supply for ac power supply, the sum of the voltages of the LED lamp strings 1, 2 and 3 is also high voltage, generally higher than 100V, the voltage of the LED lamp string 3 is equal to the battery voltage, and the battery voltage is usually lower than 4.3V, the voltages of the LED lamp strings 1 and 2 are much greater than the voltage of the LED lamp string 3, so that the total number of the lamp beads of the LED lamp strings 1 and 2 is much greater than the number of the lamp beads of the LED lamp string 3.

When the power supply is powered on, the current flows through the LED lamp strings 1, 2 and 3, namely 3 lamp strings emit light simultaneously, when the power supply is powered off, the current only flows through the LED lamp strings 3, namely only the LED lamp strings 3 emit light, a large number of lamp beads in the LED lamp strings 1 and 2 are idle, and due to the limitation of the overall cost, the number of the lamp beads in the LED lamp strings 3 is small, and the light emitting power during emergency lighting is also limited.

Usually, a driving circuit board and an LED lamp bead light source board in an emergency lamp circuit are 2 independent circuit boards which are connected through electric wires. The LED lamp string of current emergency light circuit contains LED lamp string 1, LED lamp string 2 and LED lamp string 3, has 4 electric wires between this LED lamp pearl light source board and the drive circuit board, and general LED lamp pearl light source board only has 2 electric wires on the market, so on general LED lamp pearl light source board can not be used for current emergency light circuit on the market, need produce LED lamp pearl light source board alone for current emergency light circuit.

Disclosure of Invention

The invention solves the technical problem of providing an emergency lamp driving circuit which has high utilization rate and cost saving and can be directly connected with a universal LED lamp bead light source plate on the market for use.

The technical scheme adopted by the invention for solving the technical problems is as follows: an emergency lamp driving circuit comprises a power supply, a high-voltage switching power supply driving circuit, a low-voltage switching power supply driving circuit, a power tube N1, a power tube N2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, an LED lamp string, a capacitor C1, a ground wire 1, a ground wire 2 and a transformer, wherein the transformer comprises a coil L1, a coil L2 and a coil L3;

the power supply end VCC of the high-voltage switching power supply driving circuit is connected with a positive power supply end, the ground wire end of the high-voltage switching power supply driving circuit is connected with an electric wire 2, the GATE2 end of the high-voltage switching power supply driving circuit is connected with the grid electrode of a power tube N2, the CS2 end of the high-voltage switching power supply driving circuit is connected with the ground wire 2 through a resistor R2, the drain electrode of the power tube N2 is connected with the positive power supply end, the source electrode of the power tube N2 is connected with the ground wire 2, the diode D5 is a parasitic diode of the power tube N2, the anode of the diode D4 is connected with the ground wire 2, the cathode of the diode D4 is connected with the cathode of the diode D1, the anode of the diode D1 is connected with the ground wire 1, the different-name end of the coil L2 is connected with the cathode of the diodes D1 and D48, the same-name end of the coil L2 is connected with the anode of the LED;

the negative pole of the battery is connected to a ground wire 1, the power supply end VDD of the low-voltage switching power supply driving circuit is connected with the positive pole of the battery, the ground wire of the low-voltage switching power supply driving circuit is connected with the ground wire 1, the control end of the low-voltage switching power supply driving circuit is connected with an external power supply power failure signal, the GATE1 end of the low-voltage switching power supply driving circuit is connected with the grid electrode of a power tube N1, the FB1 end of the low-voltage switching power supply driving circuit is connected with the ground wire 1 through a resistor R1, the source electrode of the power tube N1 is connected with the ground wire 1, the diode D2 is a parasitic diode of the power tube N1, the dotted terminal of the coil L1 is connected with the positive pole of the battery, the dotted terminal of the coil L1 is connected with the drain electrode of the power tube N1, the dotted terminal of the coil L3 is connected with the ground wire 1, the dotted terminal of the coil L.

Further, the method comprises the following steps: the high-voltage switching power supply driving circuit is an LED constant current driving control circuit.

Further, the method comprises the following steps: the chip type of the high-voltage switching power supply driving circuit is HV 9910.

Further, the method comprises the following steps: the chip model of the low-voltage switching power supply driving circuit is LN 2266.

The invention has the beneficial effects that: the emergency lamp circuit only has one LED lamp string, all the lamp beads in the LED lamp string are always in the working state, the utilization rate is 100%, the number of the lamp beads in the emergency lamp circuit can be reduced, and the cost of the emergency lamp circuit is saved. Usually, a driving circuit board and an LED lamp bead light source board in an emergency lamp circuit are 2 independent circuit boards which are connected through electric wires. The LED lamp bead light source board only has 2 wires with the driving circuit board, and the LED lamp bead light source board which is universal in the market also only has 2 wires, so that the LED lamp bead light source board which is universal in the market can be connected with the emergency lamp circuit for use.

Drawings

Fig. 1 is a circuit diagram of an emergency lamp of the present invention.

Fig. 2 is a schematic diagram of the LED current and battery charging current paths of the emergency lamp circuit of the present invention when the power supply is on and the power N2 is on.

Fig. 3 is a schematic diagram of the LED current and battery charging current paths of the emergency lamp circuit of the present invention when the power supply, power N2, is off.

Fig. 4 is a schematic diagram of the paths of the LED current and the battery discharge current of the emergency lamp circuit of the present invention when the power supply is off and the power N1 is on.

Fig. 5 is a schematic diagram of the paths of the LED current and the transformer demagnetization current when the power supply of the emergency lamp circuit is cut off and the power N1 is cut off.

Fig. 6 is a circuit diagram of a prior art emergency lamp.

Fig. 7 is a schematic diagram of the paths of the LED current and the battery charging current of the conventional emergency lamp circuit when the power supply is powered and the power tube N2 is turned on.

Fig. 8 is a schematic diagram of the paths of the LED current and the battery charging current of the prior emergency lamp circuit when the power supply is powered and the power tube N2 is turned off.

Fig. 9 is a schematic diagram of the paths of the LED current and the battery discharge current when the power supply of the emergency lamp circuit is turned off and the power tube N1 is turned on.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

As shown in fig. 1, an emergency lamp driving circuit includes a power supply, a high-voltage switching power supply driving circuit, a low-voltage switching power supply driving circuit, a power tube N1, a power tube N2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, an LED light string, a capacitor C1, a ground wire 1, a ground wire 2, and a transformer, where the transformer includes a coil L1, a coil L2, and a coil L3;

the power supply end VCC of the high-voltage switching power supply driving circuit is connected with a positive power supply end, the ground wire end of the high-voltage switching power supply driving circuit is connected with an electric wire 2, the GATE2 end of the high-voltage switching power supply driving circuit is connected with the grid electrode of a power tube N2, the CS2 end of the high-voltage switching power supply driving circuit is connected with the ground wire 2 through a resistor R2, the drain electrode of the power tube N2 is connected with the positive power supply end, the source electrode of the power tube N2 is connected with the ground wire 2, the diode D5 is a parasitic diode of the power tube N2, the anode of the diode D4 is connected with the ground wire 2, the cathode of the diode D4 is connected with the cathode of the diode D1, the anode of the diode D1 is connected with the ground wire 1, the different-name end of the coil L2 is connected with the cathode of the diodes D1 and D48, the same-name end of the coil L2 is connected with the anode of the LED;

the negative electrode of the battery is connected to a ground wire 1, the power supply end VDD of the low-voltage switching power supply driving circuit is connected with the positive electrode of the battery, the ground wire of the low-voltage switching power supply driving circuit is connected with the ground wire 1, the control end of the low-voltage switching power supply driving circuit is connected with an external power supply power failure signal, the GATE1 end of the low-voltage switching power supply driving circuit is connected with the grid electrode of a power tube N1, the FB1 end of the low-voltage switching power supply driving circuit is connected with the ground wire 1 through a resistor R1, the source electrode of the power tube N1 is connected with the ground wire 1, the diode D2 is a parasitic diode of the power tube N1, the dotted terminal of the coil L1 is connected with the positive electrode of the battery, the dotted terminal of the coil L1 is connected with the drain electrode of the power tube N1, the dotted terminal of the coil L3 is connected with the ground wire 1, the dotted terminal of the coil L;

the specific principle of the circuit is as follows:

when the power supply VDC supplies power normally, the power supply VDC outputs current, one part of which flows through the LED lamp strings, and the other part charges the battery, and when the power supply VDC is powered off, the battery outputs current which flows through the LED lamp strings to light the LED lamp strings for emergency lighting.

When the power supply supplies power normally, the high-voltage switching power supply driving circuit works normally, the GATE2 end of the high-voltage switching power supply driving circuit is used for controlling the working state of the power tube N2 and adjusting the duty ratio of the high-voltage switching power supply to enable the current passing through the LED lamp string to be constant, the resistor R2 is used for sampling the current, and the current passing through the LED lamp string at the moment is detected; when the power supply VDC is cut off, the high-voltage switching power supply driving circuit stops working because no power source exists, the voltage across the GATE2 of the high-voltage switching power supply driving circuit is 0 relative to the ground line 2, and the power tube N2 is turned off.

When the power supply VDC supplies power normally, the power supply power failure signal is invalid, the low-voltage switching power supply driving circuit does not work, the end of the low-voltage switching power supply driving circuit GATE1 is at low level relative to the ground wire 1, and the power tube N1 is disconnected; when the power supply VDC is powered off, a power supply power failure signal is triggered, the low-voltage switching power supply driving circuit is started to work, and the end of the low-voltage switching power supply driving circuit GATE1 is used for controlling the working state of the power tube N1 and adjusting the duty ratio of the low-voltage switching power supply to enable the current passing through the LED lamp string to be constant. The resistor R1 is used for sampling current and detecting the current passing through the LED lamp string when the power tube N1 is conducted.

The method specifically comprises the following steps: when the power VDC supplies power normally, the high-voltage switch power supply driving circuit works normally; the low-voltage switch power supply driving circuit does not work, and the power tube N1 is turned off. The emergency lamp circuit comprises 2 states shown in fig. 6 and 7 according to the working state of the power tube N2.

As shown in fig. 2, when the power source VDC supplies power normally and the signal at the GATE2 of the high voltage switching power supply driving circuit is at a high level with respect to the ground 2, the power tube N2 is turned on, and the current output by the power source VDC flows through the power tube N2, the diode D4 and the transformer coil L2, then flows through the LED string, and the current through the transformer coil L2 increases linearly and the coil L2 stores energy. In this process, the voltage of the different name terminal of the transformer coil L2 is higher than that of the same name terminal, so that the induced electromotive force of the different name terminal of the transformer coil L3 is higher than that of the same name terminal, and an induced current flowing from the same name terminal to the different name terminal is generated in the transformer coil L3, passes through the diode D3, flows to the positive electrode of the battery, and charges the battery. The induced current passes through the battery and returns to the synonym terminal of the transformer coil L1.

As shown in fig. 3, when the power source VDC is normally supplied and the signal at the GATE2 terminal of the high voltage switching power supply driving circuit is at a low level with respect to the ground line 2, the power transistor N2 is turned off. Transformer coil L2 discharges energy and the current through transformer coil L2 decreases linearly. The current through transformer coil L2 flows through the LED string and returns to the synonym terminal of transformer coil L2 through diode D1. In this process, the voltage of the same-name terminal of the transformer coil L2 is higher than that of the different-name terminal, so that the induced electromotive force of the same-name terminal of the transformer coil L1 is higher than that of the different-name terminal, and an induced current flowing from the different-name terminal to the same-name terminal is generated in the transformer coil L1, flows to the positive electrode of the battery, and charges the battery. The induced current flows into the positive electrode of the parasitic diode D2 of the power tube N1 after passing through the battery, and returns to the opposite terminal of the transformer coil L1 after passing through the parasitic diode D2.

When the power supply VDC is powered off, the high-voltage switching power supply driving circuit does not work, and the power tube N2 is turned off; the low-voltage switching power supply driving circuit works normally. The emergency lamp circuit comprises 2 states shown in fig. 8 and 9 according to the working state of the power tube N1.

As shown in fig. 4, when the power VDC is turned off and the signal at the GATE1 terminal of the low-voltage switching power supply driving circuit is at a high level with respect to the ground line 1, the power transistor N1 is turned on. The current flowing from the positive electrode of the battery passes through the transformer coil L1, passes through the power tube N1 and returns to the negative electrode of the battery. In this process, the voltage of the same name terminal of the transformer coil L1 is higher than that of the different name terminal, so the induced electromotive force of the same name terminal of the transformer coil L2 is higher than that of the different name terminal, an induced current flowing from the different name terminal to the same name terminal is generated in the transformer coil L2, and the induced current flows through the LED string and the capacitor C1, then returns to the different name terminal of the transformer coil L2 after passing through the diode D1.

As shown in fig. 5, when the power VDC is turned off and the signal at the GATE1 terminal of the low-voltage switching power supply driving circuit is at a low level with respect to the ground line 1, the power transistor N1 is turned off. The current through the transformer coil creates a magnetic field in the transformer core before the power tube N1 turns off; after the power tube N1 is turned off, the magnetic field in the transformer core is unlikely to change abruptly, so that the transformer coil L3 generates an induced electromotive force, and the induced electromotive force of the different-name terminal of the coil L3 is higher than that of the same-name terminal, thereby generating an induced current flowing from the same-name terminal to the different-name terminal of the transformer coil L3, and the current flows into the positive pole of the battery after passing through the diode D3, i.e., the excess electric energy stored in the transformer is returned to the battery. In the process, the capacitor C1 supplies current to the LED light string to keep the LED light string lighted, and the charge stored in the capacitor C1 flows out from the positive electrode of the capacitor, flows through the LED light string and returns to the negative electrode of the capacitor C1.

After the power tube N1 is turned off, the magnetic field in the transformer core is unlikely to change abruptly, so that the induced electromotive force is also generated by the transformer coil L2, and the induced electromotive force at the synonym terminal of the coil L2 is higher than that at the homonym terminal. The diode D4 is connected between the source of the power transistor N2 and the synonym terminal of the coil L2. Since the diode has unidirectional conductivity, the induced current caused by the induced electromotive force in the transformer coil L2 can be prevented from flowing to the power source VDC through the parasitic diode D5 of the power tube N2. If the diode D4 is not provided in the circuit, when the power source VDC is turned off, the power source VDC is charged by an induced current due to an electromotive force induced in the transformer coil L2, so that the high voltage switching power supply starts operating.

The emergency lamp circuit only has one LED lamp string, all the lamp beads in the LED lamp string are always in the working state, the utilization rate is 100%, the number of the lamp beads in the emergency lamp circuit can be reduced, and the cost of the emergency lamp circuit is saved. Usually, a driving circuit board and an LED lamp bead light source board in an emergency lamp circuit are 2 independent circuit boards which are connected through electric wires. The LED lamp bead light source board only has 2 wires with the driving circuit board, and the LED lamp bead light source board which is universal in the market also only has 2 wires, so that the LED lamp bead light source board which is universal in the market can be connected with the emergency lamp circuit for use.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.