mrfroggy321

[Mrfroggy321]

Am working with strings of leds, yellow and red. useing a power supply that I built useing a 317T voltage regulator. My problem is when I turn up the voltage to light up the yellow it literally smokes the red leds. My problem is that I need to build a dual voltage power supply, and I need to know what type of mini pot (5k) (as Digi-key shows a gazillion types) to use. Thanks

 

[Pommie]

Welcome Mr Frog.

Have you got current limiting resistors in series with your LEDs.

Mike.

 

[Mrfroggy321]

No resistors, want to stay away from them as there are so many leds and the number will vary from application to application. Thought it would be much simpler going with the 317T's Thanks

 

[audioguru]

If you don't use current-limiting resistors with your LEDs then they will smoke and burn.
They are diodes (not light bulbs) with a certain range of voltages. Their current has a max allowed amount.

An LM317 can be made into a constant-current-source by adding a single resistor. Then it can light one string of LEDs.
An LM317 can be made into a voltage regulator and it can light many strings of LEDs if each string has its own current-limiting resistor.

 

[blueroomelectronics]

Must be avoid resistor night, why anyone would cut out the smallest cheapest part you can get I'll never understand.