Working on a project....trying to make something cool out of a dead Super Champ XD.
The PT has a ~9vac non-center tapped secondary that I am not using for anything else so I figure I'll use it to power an LED. I've done this several time from the heater supply with no issues, but...
Do I need a ground reference? This secondary will be used for the LED only.
Further to Martins advice,
In case you were wondering - The reason for the power diode in series is that LEDS have a reverse voltage rating of ONLY about 6 volts. The series power diode will handle the reverse voltage and stop the LED from blowing up.
Cheers,
Ian
Further to both advices: a series diode lets the LED light and prevents reverse breakover, but the current in the windings feeding it is only half-wave rectified. Putting a second diode in parallel with the LED, but reversed, so the LED conducts one way, the diode the other, can be quieter in some situations, because current flows both directions and is less harmonic-rich.
A third way is to use a small 1A full wave bridge, which can be as small as a 6-pin DIP package, and connect the LED across the DC outputs, with the AC voltage after the series resistor connected to the AC terminals of the bridge. Now the LED lights on both half cycles, the current is symmetrical per half cycle, and the flicker rate on the LED is upped from 60 Hz to 120Hz, which is perceptible in some situations to some people.
