An LED Power Supply Modification

 

 

 

June 16, 2016

A while back I discovered that LED lighting really came of age. That you can buy 10 watt modules on ebay for $.50 a piece, cinched it. Thing is you need a constant current power supply for LEDs and most supplies on the market are constant voltage. In this case I'm modifying a small 12V, 3A, framed supply you can get for ~$6. Better is to use a 72 watt LCD Supply as they cost about the same.

 

 

 

12V 3A supply

 

 

 

Yea, this picture is not in great focus. What happens here is to cut the trace to the positive output lug. Then solder two reasonably sized wires on each side of the cut. The two green wires in this case.

 

 

 

Trace Cut


 

 
The voltage regulator in just about all cases will be an 'on to limit' opto-isolator. This one is driven by a TL431. This is very typical on small switchers. I've left out a couple of components that are not necessary for this discussion.

PS Regulator


So by adding this circiut to the low voltage output you now have a current regulated power supply.


Current Regulator

The transistor turns on with about a little more than a .6 volt drop across R1. It is .25 ohms so that comes out to 2.5 amps. It is a bit wasteful, the resistor is going to dissipate some 1.5 watts. If you are running 5 or more chips I would look at doing them in series and high voltage. Or using an op amp and a voltage drop of some tens of millivolts.

The LED chips operate at about 9 volts at this current. More than enough for me, the lights are as bright as I've seen them The last set had a rather short life time as I let the supply run full out. Here is the board:

installed


And here they are in service, the little middle one:

working


I'm phasing the fluorescents out of the shop.....

Thanks, Dan.

 

 

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