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At present, most LED lamps have the same level of complexity as the control power supplies used in emergency lighting, and 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 independent system, which can be used in conjunction with LED drive power of different powers, which is simple, convenient and flexible to use.
When the mains power is normal, the LED drive power supplies power to the control board and drives the light source to emit light. Mains charges the battery through the charger. After the battery is full, the power is cut off by the protection circuit to stop charging. When the mains power is cut off or braked, the battery provides power to the emergency part of the light source, and supplies power to the emergency light source through the emergency control circuit.
In the design, the emergency light source may be the whole or part of the normal lighting source; the normal lighting source and the emergency lighting source may be separated separately, or may be made as a whole. Just adjust the peripheral circuit a little.
The emergency control circuit is a relatively novel and unique place in this design. It is mainly composed of MT7201 chip, peripheral circuit and relay. With the external detection part, it 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 the electrical layout of the new LED emergency lighting fixture of this design is very different from the emergency lights commonly used now. At present, the commonly used emergency lamps are composed of circuits such as voltage transformation, voltage regulation, charging, inverter, and battery. The back end is then connected to the LED driving power supply to supply power to the LED light source. The advantage is that both ordinary lamps and LED lamps can be used, and the application range is wide. The disadvantage is that there are many electronic components, it is difficult to repair, and the failure rate is high; and after the design is completed, the adjustment of the power level is fixed is inconvenient, the circuit is working during 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 lamps. It only needs to adjust few components and can be used in conjunction with peripheral LED power supplies and other LED lamps of different powers; only part of the circuit of the LED driving power supply works during normal lighting. The power consumption is low, and the corresponding failure rate is also low.
Among them, MT7201 is a continuous current conduction mode buck constant current source, which is used to drive one or more LEDs in series. Its input voltage range is from 7V to 30V, and the output current is adjustable, up to 1A. According to different input voltage and peripheral devices, it can drive up to 24W LED. MT7201 is available in SOT89-5 package.
The average current of the LED in the circuit is determined by the resistance Rs connected between Vin and Isense: the relay uses a small relay that is normally open and normally closed. The detection part uses a microwave radar remote control switch. When the human body or object enters the detection range, the sensor immediately Work and start the controlled equipment. When the human body leaves or the object stops moving, the sensor will automatically stop working after the delay time, and the sensor will enter the detection state. If the object continues to move within the detection range, the sensor is always in working condition. Of course, the detection part can be replaced with infrared, sound control, light control, etc. as needed.
If the LED is open, the inductor will lose connection with LX, and no current will flow through the entire loop, which will not cause damage to the device.
A bypass capacitor with low equivalent series resistance (ESR) must be connected to the power input. The greater the ESR, the greater the efficiency loss. The bypass capacitor should be able to withstand a large peak current, and the input current of the power supply can be averaged to reduce the impact on the input power supply.
For DC input, the minimum value of the bypass capacitor is 4.7uF. For AC input or low voltage input, the bypass capacitor requires a 100uF capacitor or similar. The bypass capacitor should be as close as possible to the input pin of the chip.
The recommended inductance parameter range of MT7201 is 27uH ～ 100uH. The saturation current of the inductor must be 30% to 50% higher than the output current. The selection of the inductance value needs to take into account the working duty ratio and the opening and closing time of the power switch to ensure that the requirements in the electrical characteristics table are met.
When the mains power is cut off, the emergency circuit supplies power, the battery voltage is 26.4V; the output current is adjustable, set here to 300mA; the relay input voltage DC12V, emergency light source power 5.5W; emergency light source voltage 18V.
The design circuit is simple and reliable, the power is adjustable, and the layout of the emergency light source and the whole light source is flexibly arranged according to the actual situation. It is widely used in factories, mines, tunnels and other areas that require emergency lighting.
Linsheng specializes in the production and supply of high-quality LED emergency light products. Have its own laboratory and the most advanced testing equipment in the industry to ensure product quality. It is one of the professional Emergency Light Suppliers in China. In addition, we have obtained ISO9001-2000 and BSCI certificates. Our products are exported to customers in countries and regions such as the United States, Europe, Africa and Asia. We also welcome OEM and ODM orders. Whether you choose the current product from our catalog or seek engineering assistance for your application, you can contact our customer service center to understand your purchasing requirements.
