Design of a new LED emergency light control circuit

Jiangmen City Pengjiang District Qihui Lighting Electrical Appliances Co., Ltd

November 06, 2022

Qihui lighting LED emergency lights are mainly used to provide emergency lighting after the normal lighting power supply is cut off or the power grid is cut off. Commonly used in factories, mines, institutions, schools, buildings and tunnels. The emergency lighting system used in my country is mainly controlled by its own power supply. The general power supply is connected to the general lighting power circuit. The LED emergency light battery is charged normally. When the normal power supply is cut off, the LED emergency driver (battery) automatically supplies power. This type of fire emergency light has a large number of electronic components such as transformers, voltage regulators, charging, inverters, batteries, etc. inside the lamp. Batteries need to be charged and discharged during use, maintenance and failure.
The other is a centrally controlled power supply. Emergency lights do not have an independent power source. When the normal lighting power supply fails, it is powered by the centralized power supply system. In this form of emergency lighting system, all the complex electronic circuits inside the lamps are omitted, the emergency lighting lamps are no different from ordinary lamps, and the centralized power supply system equipment is located in the dedicated computer room.

At present, the control power supply of most LED lamps and ordinary lamps is the same in complexity. The power of each control power supply is fixed and cannot be adjusted according to actual needs. The LED emergency control circuit designed in this paper is a complete and independent system, which can be used with different power LED power supplies. It is simple, convenient and flexible to use.

1. Principles and advantages and disadvantages of new LED emergency lighting

The block diagram of this new type of LED emergency lighting is as follows:

Figure 1 Block diagram of new LED emergency lighting fixtures

When the commercial power is normal, the LED driving power supply supplies power to the control board, and drives the light source to emit light. The utility power charges the battery through the charger. When the battery is fully charged, the protection circuit cuts off the power and stops charging. When the mains is cut off or disconnected, the battery supplies power to the emergency part of the light source, and the emergency light source supplies power to the emergency light source through the emergency control circuit.

In this design, the emergency light source can be all or a part of the normal lighting source; the normal lighting source and the emergency lighting source can be separated, or the whole can be separated. Just need to adjust the peripheral circuit slightly.

The emergency control circuit is a relatively novel and unique place in this design. It is mainly composed of MT7201 chip, peripheral circuits and relays. The external detection part can be designed into microwave radar detection emergency lighting, infrared detection emergency lighting, voice control, light control and other forms.

This emergency control circuit determines that the electrical layout of the new LED emergency lighting fixture designed in this design is very different from the emergency lights currently used. The current emergency lighting is composed of transformers, voltage regulators, chargers, inverters, batteries, etc., and the back end is connected to the LED drive power supply to supply power to the LED light source. The advantage is that both ordinary lights and LED lights can be used, with a wide range of applications. The disadvantage is that there are many electronic components, maintenance is difficult, and the failure rate is high; it is inconvenient to adjust after the fixed power level design, the circuit works in the normal power supply, and the power consumption is high.

Second, the emergency control circuit principle and test results

The emergency circuit of this design is dedicated to LED lights. Only need to adjust a few components, it can be used with peripheral LED power supply, suitable for LED lamps of different power. During normal lighting, only the LED drive power part in the circuit works. The power consumption is low, and the corresponding failure rate is also low. The circuit principle is shown in Figure 2.

Figure 2 Schematic diagram of emergency control circuit

The MT7201 is a continuous current conduction mode step-down constant current source for driving one or more LEDs in series. Its input voltage range is 7V to 30V, and the output current is adjustable up to 1A. Depending on input voltage and peripherals, LEDs up to 24W can be driven. The MT7201 is available in a SOT89-5 package. Its pins are shown in Figure 3.

Figure 3 MT7201 pin diagram

The average current of the LED in the circuit is determined by the resistance Rs connected to both ends of Vin and Isense: the relay adopts a normally open and normally closed electric shock small relay, and the detection part adopts a microwave radar remote control

Led Emergency Light