Monday, March 18, 2013

Cheaper LED driver

Ideally, we want to drive LED with constant current driver. So after high efficient switching power supply, a constant current can be apply to LED (module) and emit desired and stable light.
However, constant current driver are less popular and more expensive  That's why there are request out there asking to use constant voltage driver, which can be 10~20% cheaper.
We have a Chinese customer asked to build a 16W LED lamp with lowest possible cost. Here is our design process.

First, we found out forward voltage of LED would decease when they are heat up. Our test shows when applying a 1.5A constant current, Easy LED module has 10.6 Volts when started working, then drop to 10.3 or even lower forward voltage. So using a very popular 12V constant voltage driver and  two diodes to drop 1.4 Volts to 10.6V was not a good idea.

However, using a resister is a good idea. an 1 Ohm resister would drop 1 volt when 1A current passing through. When team up Easy LED module with an one Ohm resister and connect to 12V constant current supply. We see current started from 1.35A and get stable at 1.5A in three minutes.
This design is indeed cheap. a 2 watts 1 Ohm resister is like a cent when high volume, a constant voltage driver are more likely less than $5. Our Chinese customer are very happy with the light output and the cost..
However, this design is not without drawback. The resister will consume another 1.5 Watt of power. This defeated the purpose of energy efficient a little bit.