# How can I power and dim two sets of LED lights where one requires12VAC and one 12VDC

I am building a wall unit and I would like to use some LED Tape Light (12VDC, 48ft Total 1.45W/Foot) to light the shelves. Then I'd like to use a 12VAC adjustable LED spot light (5W) for the center area. I'd like to have all lights able to be dimmed by using either an ELV or standard in-wall dimmer.

I think I can basically use the 12VAC electronic transformer and then use a full wave bridge rectifier (and maybe some caps?) to turn the 12VAC into 12VDC for the LED Tape lights. Is this correct? The 12VAC will be output at 20kHZ. Will frequency play any issue here? I can use a standard magnetic transformer as well if that makes things easier.

Any suggested schematics or part numbers would be helpful. The total DC load will be ~75W with AC load will be ~5W.

EDIT:

Here is the transformer I'm considering using.

WAC Lighting: EN-12100-RB-AR http://www.waclighting.com/data/TOOLS_SPEC/en-1260-rb-ar.pdf

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What is a "12VAC electronic transformer"? Can you link to a datasheet for what you're thinking about using? –  HikeOnPast Dec 4 '12 at 2:42
What's your budget? 250W or 350W surplus PC PSU will handle the 12V easily but dimmers requires custom mods. THat's what I use. –  Tony Stewart Dec 4 '12 at 3:44

For the 12 Volt DC dimmer, this answer provides suggestions like this one

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Thanks. But, needs to be powered by wall 120V dimmer. –  jr. Dec 4 '12 at 14:04

A crude but usable solution is to use a standard triac wall-mounted 120VAC dimmer for each line - such as the smoothly variable ones used for ceiling fans. Each dimmer's output would then be wired to separate 120V-->9VAC (for strip light) and 120V-->12VAC (for AC LED lamp) step-down transformers.

There are multi-channel dimmer fittings available as well, which might better suit your purposes.

The LED strip lights are then driven by a full bridge rectifier with reservoir capacitors. The flicker, if any, on the LEDs will be at twice the line frequency, hence barely perceptible but not distracting. The reason to use a 9 Volt transformer instead of 12 Volts for this, is that after rectification 9 volts would result in 9 * 1.4142 = 12.73 Volts DC, which would be within tolerance for the strip.

The "12 Volt AC" lamp would be driven straight off its transformer. Depending on the lamp's internal circuitry, this should work fine: A couple of CFL lamps in my house don't take kindly to triac-dimmed input, but most other fittings work fine.

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I think this is the route I plan to go. Drive the 12VDC lights of the 12VAC transformer using a full bridge rectifier. The transformer will be an electronic transformer so the output will be 12VAC @ 20kHz, so that shouldn't be noticeable flicker at all. –  jr. Dec 5 '12 at 13:02
@jr Do watch out for the actual DC voltage output by your rectifier: Depending on the AC waveform, the DC could be a fair bit higher. Roughly 1.4142 multiplier is a good assumption if the AC is a sine wave –  Anindo Ghosh Dec 5 '12 at 14:37
You are saying the output of the DC will be about 1.4X higher than the peak-to-peak AC voltage? –  jr. Dec 5 '12 at 18:51
@jr. No, but transformers are typically rated for RMS voltage, not peak to peak. Please share a link for the transformer in question. –  Anindo Ghosh Dec 5 '12 at 19:00

Can you link to the AC LED, as the LEDs themselves surely works with DC. If you can find out how the AC LED spotlight works/how the driver circuit looks, you should be able to power all the LEDs via DC dimmed by PWM.

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interesting Idea. I can look into that. –  jr. Dec 4 '12 at 14:04