# LED circuit

Discussion in 'LEDs and Optoelectronics' started by jpeg666, Aug 12, 2012.

1. ### jpeg666

3
0
Aug 12, 2012
I am creating a small grow light for plants

Okay Hopefully there is someone in here that can help me. I have 6 super bright (blinding) 3 watt red bridgelux LEDs I want to have them as supplemental lighting around the foliage to my current Fluorescent lighting.

I have a wall plug transformer that outputs 12v AC at 1 Amp I need help building a circuit to power these leds. I know I need to rectify the AC current to DC current and I need help with that too.

If anyone can help me with making the circuit I would be very grateful.

as for the 12V AC doesn't that mean I have 16.96 Peak voltage? Because the 12V is the RMS and the 16.96V is the actual voltage?

2. ### Alchymist

26
2
Apr 16, 2011
12 volts ac is an rms value which is equivalent to 12 volts dc power wise. While a power supply (unregulated) made of diodes and capacitors will reach a higher voltage unloaded, when loaded the voltage will drop until as the load increases to maximum the voltage will bottom out at 12 vdc. Regulated power supplies use various methods to counteract the no load to full load variations.

Designing a power supply for your leds start with the spec sheet for the leds - Ifwd,, rated voltage, etc.

3. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
The best solution is to rectify and filter (a little) the AC and use a constant current driver for the LEDs.

You have enough overhead that you can probably connect a bridge rectifier, an use an LM317 or similar set up as a constant current source.

12VAC means 12V RMS AC. Yes your peak voltage is something like what you say, but that doesn't mean it's the "real voltage"

If you draw 1A from this power supply after rectification and filtering you will be overloading it. I would recommend no more than 700 mA.

3
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Aug 12, 2012
5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Last edited: Aug 12, 2012