Help with power supply and indicator led

[spoontex]

Hello,

I'm planning to build a pedal power supply. But I want that when I plug the dc jack to the 9v output a led indicator light in that plug. How can I do this? I think in a comparator opamp or maybe a relay?? I don't know how to do this.

Anybody can help me?

[Phoenix]

A small value dropper resistor in series with the input with the regulator, there will always be some voltage drop across it due to the quiescent current of the regulator, but the voltage drop will increase once current is drawn from the regulator. The trick will be getting the threshold for the comparator sensitive enough (may require adjustment trimmer, the quiescent current draw of the regulators will vary some, even in the same batch).
That should get you started.

[EBK]

If you use output power jacks with built-in switches, you can use the switched 9V (which gets disconnected when a plug is inserted) to control a transistor that turns the LED on or off.

[spoontex]

With a transistor, of course!!! Thanks.

And for AC voltage?

[GibsonGM]

With a transistor, of course!!! Thanks.

And for AC voltage?

You can rectify it before sending it to a transistor, which will only work with DC....

[spoontex]

Something like this?

[merlinb]

Something like this?

Yes, but you can use a much larger base resistor (U$2), like 100k.
Also, your LED current is painfully high. Increase U$1 to a more suitable value, like 2.2k.

But this forum always over-engineers things. Here's a simpler way:

[EBK]

But this forum always over-engineers things.

I learned my lesson from last time.  This time, I was just setting some bait to get the easy solution to show up.   

[spoontex]

Me too. Sometimes there is always a easier solution.

Of course, led is a diode...

Many thanks.