AC Power for LEDs?

[MrTonesNZ]

I'm planning on building a signal splitter and switch box to go with my new Digitech Whammy. It will be entirely passive apart from the fact that i want indicator LEDs to go with the switches.

What I want to do is use the same power supply as the whammy to power my LEDs. It's 9v AC 1300ma.

All I want to know is, does AC power need to be treated differently when just powering LEDs? Or can I just wire it up as I would DC?

[jonny]

Normally you'd put another diode in the opposite direction as the led for the negative half of the cycle. Although using 9V it might be okay? I'm not too sure

[MrTonesNZ]

Normally you'd put another diode in the opposite direction as the led for the negative half of the cycle. Although using 9V it might be okay? I'm not too sure

Opposite direction? How so?

[jonny]

http://www.turbokeu.com/myprojects/acled.htm

[MrTonesNZ]

http://www.turbokeu.com/myprojects/acled.htm

Thanks jonny, but this is for powering an LED with Mains power. I just want to use 9V. I see what you mean about the diode now though. I wonder If the Cap is necessary with 9v too? Maybe just a small value

[jonny]

Yeah but it's just the same just give it a go should be fine (just use a much smaller resistor not=100k maybe 20k max if using a ultrabright), and i don't think you'll need the cap.Add the other diode for reverse protection for the negative cycle.

[Gurner]

In my opinion (& I've never done what your trying), you can just treat your AC as DC here (though you ight want to check your LED's datasheet for maximum reverse voltage to make sure it's more than 9V) ....the AC is normally quoted as an RMS value, therefore you can use one of the plethora of online LED calculators...

http://led.linear1.org/1led.wiz    inputting 9V as your supply.

Connect it up whichever way you prefer ...... eg connect your anode to your 9V AC supply, with the cathode connected to a current limiting resistor to ground.

If connecting as per my example, the led will go out on the negative swings (since it's reverse biased) but persistence of vision should mask any flickering.

[MrTonesNZ]

Yeah but it's just the same just give it a go should be fine (just use a much smaller resistor not=100k maybe 20k max if using a ultrabright), and i don't think you'll need the cap.Add the other diode for reverse protection for the negative cycle.

Alright, i'll trust ya!

[PRR]

> check your LED's datasheet for maximum reverse voltage to make sure it's more than 9V

It is usually specified as 5V, is often about 7V.

The LED _will_ reverse-breakdown.

However this is not fatal, as long as current is limited. If you set your forward current to any reasonable value, say 10mA, the reverse current will be a little less, reverse dissipation similar or a hair more, the LED will probably live forever.

Taking 9V supply and 2V in LED gives 7V in resistor. Taking 10mA gives 7V/10mA= 7V/0.010A= 700 ohms. Less will work just a hair dimmer, try 1K.

There may be other problems.

LED on AC will flicker. If you move your eye quickly you see after-trail like old hallucinogenic drugs. I find it mildly annoying, but perceptions differ.

LED on AC will make large BUZZZ. As an amplifier pilot-light in the far corner of the chassis, there's little problem. Inside a small tight stomp-box, it may contaminate your precious audio.

[MrTonesNZ]

> check your LED's datasheet for maximum reverse voltage to make sure it's more than 9V

It is usually specified as 5V, is often about 7V.

The LED _will_ reverse-breakdown.

However this is not fatal, as long as current is limited. If you set your forward current to any reasonable value, say 10mA, the reverse current will be a little less, reverse dissipation similar or a hair more, the LED will probably live forever.

Taking 9V supply and 2V in LED gives 7V in resistor. Taking 10mA gives 7V/10mA= 7V/0.010A= 700 ohms. Less will work just a hair dimmer, try 1K.

There may be other problems.

LED on AC will flicker. If you move your eye quickly you see after-trail like old hallucinogenic drugs. I find it mildly annoying, but perceptions differ.

LED on AC will make large BUZZZ. As an amplifier pilot-light in the far corner of the chassis, there's little problem. Inside a small tight stomp-box, it may contaminate your precious audio.

No id keep it entirly seperate