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LED lamp circuitry

LED Lamp Tear Down

I think, it is a part of human nature, to probe and to discover, to find out how and why things work the way they do. As a part of my madness, recently I dismantled an AC230V LED lamp hung on my lab with 3 high-bright 1W white LEDs, and unboxed the ‘China’ secrets. If you are new to power LED Lamps, this article should help you to get off to a good start to understanding and working with today’s LED Lamps.

Design Review

In the LED lamp, 3x1W white LEDs are wired in series. Each 1W LED has a forward drop voltage of about 3V and draws current upto 260mA. This LED network is connected to a small circuit board populated with leaded and leadless electronic components. Input of the LED driver board is AC 230V and its output voltage is DC 9V.

I found that this universal circuit board is designed as a 3W driver with constant current output suitable for LED lighting. The dc output voltage changes with the number of connected LEDs while the drive current remains constant. That is to say, in case of a single LED, the output voltage is about 3V, but this voltage level increases upt o 9V when all three LEDs are connected.

Circuit Diagram

The circuit is built around an 8-pin SMD IC – SM7523B. SM7523B is an SMD chip designed for use with off-line low-power AC/DC switching power supplies. The ‘constant primary control power switch” – SM7523 is packed with amazing features including internal chip-by-cycle peak current limit, feedback overvoltage protection, output open/short circuit protection, and soft start power-protection.

SM7523 led driver circuit

table

特点 ???

Google notified me that almost all components of this circuit is available through many online vendors. For example, a vast range of readymade EE ferrite core transformers are listed like “EE10-7523-A-type horizontal high frequency transformer for LED Light”, “EE13-YF-9V-B-type vertical high frequency transformer for LED Light”, etc.

Unfortunately the chip’s datasheet is in chinese, filled with these strange 恒流原边控制功率开关 drawings. Since Google translation does not help me much, I failed to catch the divider (R3/R2) formula. Anyway, I removed SM7523 chip from the circuit board (now it is in my smd storage box). What is next? I don’t know!

LED-5

I have a resistless temptation to build my own AC230V LED Lamp using a dedicated LED driver chip. So, I am planning to move towards such chips from NXP, and ON semiconductors. Now I am referring countless datasheets to handle the task at hand, including:

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