Environmentally friendly and energy-saving LED AC/DC dual-purpose lamp

This environmentally friendly "12W" LED AC/DC dual-purpose lighting lamp (self-lighting) uses 12 1WLEDs to form a fluorescent tube. Its illumination is greater than 1000Lux, which exceeds the brightness of ordinary 40W fluorescent tubes. It is indeed a fashionable new light source. Its core circuit consists of a four-op-amp LM324 to form a constant current source power supply circuit and a DC undervoltage indication circuit. It has a perfect structure and reliable performance. It has the characteristics of energy saving, environmental protection, high efficiency, and long life. It is suitable for family lighting, especially in rural areas and areas with unstable city power. Therefore, an AC/DC automatic conversion function is added to it, which can provide emergency power supply in case of power outage.

1. Circuit structure

The LED dual-purpose lighting lamp is shown in the attached figure. (1) Power supply circuit: The main power supply is a commercially available 24V/1A switching power supply, and the other is an emergency power supply composed of two 12V/7Ah batteries. (2) Lighting circuit: LED1~LED6 and LED7~LED12 are connected in series to form two groups of light-emitting diode components, which are powered by two groups of power supplies respectively, with a rated current of 350mA and a terminal voltage of 3.3V~3.5V. (3) Reference and constant current source circuit: Vs forms a 2.5V reference source and is cascaded with a voltage follower composed of Al. Op amps A3 and A4 and their output terminals are respectively connected to transistors Q1 and transistor O2 to form a constant current source circuit, where R3 and Rll are sampling resistors that determine the constant current size. (4) Undervoltage indication circuit: Op amp A2 and resistors R6, R7 and R8 form a hysteresis voltage comparator to detect the voltage change of battery Ec. Once it is lower than the normal working voltage, LED13 lights up to indicate undervoltage.

2. Working Principle

See the attached figure, the mains power Vi is turned on, and the AC/DC switch converter converts it into a 24V DC voltage for each level of working voltage. First, VS generates a 2.5V reference voltage and sends it to the third pin of the op amp. Its first pin output is also 2.5V. After filtering by Cl and then divided by resistors R4 and R5, a 1.25V stable voltage is provided as the reference voltage of the constant current source, which is sent to the fifth pin of the op amp A3 and the tenth pin of the op amp A4 respectively. Its output is amplified by transistors Q1 and Q2 respectively. Resistors R3 and Rll are respectively connected to the sixth pin of the op amp A3 and the ninth pin of the op amp A4. Through the inverting input, it is compared with the in-phase "reference" to ensure that the two collectors output a constant current of about 340mA, which respectively illuminates the two groups of light-emitting diodes LED1~LED6 and LED7~LED12 components. The output formula of its constant current source is Is=1.25WR, where R is the sampling resistor value. When the city power outage occurs, the relay K1 is released, the internal switch K1 is turned on, the battery Ec is automatically switched, the two sets of lights are continuously lit, and everything works as usual, which is called "emergency lighting". Here, the operational amplifier A2's pin (12) is connected to the reference 2.5V, and the pin (13) detects the battery EC through the variable resistor W1. Once it is lower than 20V, the voltage comparator A2 flips, and the output pin (14) becomes high level, lighting up LED13, telling the battery Ec that it must be charged.

3. Assembly precautions

There are no special requirements for the components used. Currently, the price of 1W LED has dropped to only a few yuan, and 12 pieces can meet the requirements of home lighting. The switching power supply specification is 24V/1A, and the model is optional. It must be installed on the lamp holder. It can also be replaced by a power transformer and rectifier source with a primary of 15W~20W and a secondary of 20V, but the power consumption will increase by nearly one-fold. The integrated circuit operational amplifier LM234 is a universal device with 14 pins of dual in-line plug. Wl is a multi-turn potentiometer, model 3296. The voltage of relay Kl is 12V, model 4100. The light-emitting diodes LED13 and LED14 are selected to be 5mm. The colors are red and green for distinction. When assembling, a fluorescent lamp shell with a translucent cover should be selected, the transformers at both ends should be removed, the switching power supply should be installed on one end, the two circuit boards should be installed on the other end, and the light-emitting diodes should be installed in the middle. The steps are as follows: (1) Find an aluminum bar of suitable length as a bracket. (2) Fix the 12 LEDs together with the heat sink on the bracket. (3) When installed in the lamp holder, the screws must be tightened and cannot be rotated.

There are two places to debug when welding the printed board: the constant current source circuit, that is, whether the current at the two collectors is 340mA~350mA, otherwise change the resistance of R5 to 3.9kΩ~4.7kΩ. Calibrate Wl when the battery Ec is close to 20V, LED13 should light up, the external "emergency power supply" line and the power switch Sl are installed outside the machine, and the rest are operated normally. This lamp has been actually used for at least 10 years without changing the LED lamp, there is no electronic waste, and it contributes to environmental protection.