Trying to find a cheap and effective way to dim my panels, I made a lot of research around to web to find the right solution. Finally I found out some nice voltage regulators that can be used with a very basic circuit and make an excellent job. The LM338 is a 5A variable regulator that can manage any voltage among 3 and 36V and that with a simple trimmer/pot and a resistance drop down the voltage up to a defined value. It’s very cheap (2 Euros or less) and with as much as 10 euros of components you can make a board that can support up to 250 leds or 50 grain of wheat bulbs. Downside is that the much power it has to dissipate the much it will get hot, so an heatsink is required when you use it with 9V or up supply.

The circuit is basic. The LM338 in the TO220 package just has 3 pins, Input, Output and regulation. the output pin is connected to a 120ohm resistor as feedback and tied together to the output pin of the pot. The regulation pin is connected to the pot to variate the voltage down. There are many calculators around the web to choice the right pot max resistance in relation to the needed application.

A smaller version with 1.5A is also available, the LM317. But because of the very cheap price I would anyway go for the LM338.

You can have further information about here.

written by l45 captain \\ tags: board, bulbs, circuit, dimming, leds, pcb