Powering LEDs from Negative Voltage

[yano]

I've got a MAX1044 generating negative voltage off of a +9V line and I'd like to have a power indicator...that also indicates the 1044 is working. The easiest way I can think of to do that would to just power the LED off of the negative voltage supply. Is this possible?

[petemoore]

As long as you're measuring 9v difference.
 You may have to turn the LED around for it to light.
 Use a 4k7 or better resistor on the LED, so it doesn't burn out.
 I'm assuming you're planning a 3PDT bypass w/indicator setup...the only thing I think of is the small PS needs of the LED that probably won't be a bother.

[yano]

Thanks, I'll try this out with my breadboard...I was worried that I might fry my led.

Actually, the light is a power indicator for a mixer i'm working on....No batteries involved, its strictly jack powered, so I don't really care how much power I draw.

[smoguzbenjamin]

You should care. If you over-do the current draw you'll fry your PS. Make sure that your PS will be able to supply enough current, preferably with a 30% safety margin!

[Samuel]

an LED can't pull much more than 20mA can it? Or am I misunderstanding?

[smoguzbenjamin]

You're right, I also use 20mA for a max LED rating. But 20mA is quite a lot, considering that an effect circuit will probably draw only a quarter of that