Electronic – Power dissipation when connecting LED to +-15v


In my audio project that is powered off dual +/-15v rails, I would like to connect a simple LED indicating power on. However, when I connect it with a 1.5k resistor in series (2W), the ~28V dissipated as heat are excessive and the resistor gets very hot (too hot for touching).

What is the best way of dealing with this? Should I use two larger value resistors in parallel with each other so they share the heat? Should I connect it just between + and GND instead of between + and -? Wouldn't that put a imbalance in my rails used mostly for op-amps?

Best Answer

The first thing you should do is to increase the resistance. Using 20 mA for an indicator LED might have been necessary 30 years ago, but today you're perfectly fine with 2 mA. With an order of magnitude lower current, you won't have the same problem with heat dissipation.

To your second question, with regards to imbalanced rails, that is a non-issue unless your power supply is already so close to its maximum spec that the additional 2 or 20 mA will make it choke. Your op-amp already draws a very imbalanced current from the negative and positive rails, depending on the audio material.