I want to add an LED to my PSU which lights up when current is flowing. The obvious way is this:-
but the voltage drop is dependant on the amount of current flowing. A couple of diodes get 'round this to a degree but at low currents don't seem to drop enough and, as with the resistor, 'waste' a couple of volts.
What I'd like to be able to do is switch it through a transistor but can't think how.
This is especially maddening as I know I did it fifteen or so years ago but am jiggered if I can remember how; it must have been simple if I could have devised it.
Any suggestions greatly appreciated.
- Joe
but the voltage drop is dependant on the amount of current flowing. A couple of diodes get 'round this to a degree but at low currents don't seem to drop enough and, as with the resistor, 'waste' a couple of volts.
What I'd like to be able to do is switch it through a transistor but can't think how.
This is especially maddening as I know I did it fifteen or so years ago but am jiggered if I can remember how; it must have been simple if I could have devised it.
Any suggestions greatly appreciated.
- Joe
