DC power supply

[e67]

I have one of those Chinese Longwei dc power supply boxes......it has constant voltage and constant current options... I haven't figured out yet what you would use constant current for??
what do you know??

 

[MurphyGuy]

Constant current is used for LED lighting to prevent thermal runaway.

It's not always needed. For example, if you have a single led light rated for 12vdc and 1000ma, and you run it at 11 volts, it is unlikely thermal runaway would ever occur. But if you have a long string of lights and one of them shorts out, the voltage will climb on all the others.. this isn't a problem if you have constant current control, but it will kill the entire string if the voltage climbs, which causes increased current, and the individual LED's start to go into thermal runaway.