Indicator LEDs

[bacterozoid]

See attached file - is this the way I should add indicator LEDs? When the switch is thrown to turn the output for a given voltage on, the LED turns on with it at 20mA. I've not done indicator LEDs before, so I'm not sure what the best approach is. Thanks!

 

[ccurtis]

Yep. You will have more like 18 mA through each LED since the LED drops somewhere between 1 and 2 volts, depending on the LED's color. Resistors should be 1/2 watt or higher. 1/4 watt resistors, power would be exceeded.

 

[ccurtis]

Also, if you put the LEDs on the output side of the regulators, they convey regulator output functionality in addition to input voltage functionality. Your choice.

 

[bacterozoid]

That's a good point, actually. There's probably no way to do that on the adjustable regulators, though, right? In order not to burn out the LED, I would need something like a 600 ohm R, which then only allows 2mA at low voltages, and about 20mA at the max voltage level.

 

[ccurtis]

Agreed. Generally, though, you will want to adjust the voltage on a variable output to some level before using it -- thus ensuring functionality at the same time. Purchased supplies usually have a built-in panel meter to make that easy and to allow monitoring.

 

[bacterozoid]

Yeah, I debated that for a while...it would be nice to have that sort of display, which would negate the need for the LED "working indicator", as you mentioned. I don't know of any really simple way to do this, so I imagine I'll just use a multimeter to set it when necessary.