# Just a simple question?

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#### estarapapax

##### New Member
Please look at the very first image in the page provided by this link:

http://www.aaroncake.net/Circuits/supply.asp

My problem is very simple. I currently don't have any idea on how I will add a LED in that circuit so that whenever a load is connected (of course Vin must be connected to the outlet), the LED will light up. I doubt if I will just put it in series with the load. Just tell me the nodes to connect and if additional resistors are needed. Or maybe just provide me a link which has a similar circuit but with a LED. Thanks.

#### Willbe

##### New Member
how I will add a LED in that circuit so that whenever a load is connected, the LED will light up.
Inside of a high-side switch, this is a high-side sensing circuit.

To turn on a transistor, you need about a minimum of 0.7v, b to e. 5A at 0.7v is 0.14Ω and dissipates ~4w. Put this current sensing resistor in series with the reg. IC input line.
This resistor needs to be adjustable; I'd make this resistor out of about 1' of #30 wire wrap wire.

Hook up a PNP transistor with the e terminal upstream of this resistor and b terminal downstream. Put a 1kΩ resistor in series with the base lead.

Run the collector lead through a 40/.02 = 2kΩ resistor through your LED to ground.
The breakdown voltage of this transistor needs to be >40v.

If you need a snap-action turn-on for the LED, or if you need the LED to turn on at very low load currents, this circuit will get more complicated.

#### audioguru

##### Well-Known Member
The values of the resistors in the project are for the more expensive LM117. They should be a 120 ohm resistor and a 2.5k pot for an LM317.

#### mneary

##### New Member
They should be a 120 ohm resistor and a 2.5k pot for an LM317.
This is also the correct value for the LM338K.

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