# Designing a power supply that drives an LED array supply

I want to drive an LED array from mains power. The wall switch has a dimmer on it, I'd like the intensity of the LEDs to reflect the relative position of the dimmer, so as I dim the switch, the intensity of the LED array drops.

Because I already have an 8V 12W Halogen bulb system in place, I want to replace it with as few parts as possible to convert it to LED.

I'd like to do this as simple as possible. I know there are more sophisticated circuits that could utilize MCU or other clock driven PWM, but I am wondering if there is a more simple solution I am overlooking.

My current plan was to use a step down transformer / rectifier circuit. I would calculate the maximum DC voltage available when the dimmer was turned all the way off, apply the correct resistors to limit the maximum current in this "max voltage" scenario, and then use a simple constant voltage regulator circuit to control the intensity of the LEDs as I dimmed the circuit.

Would this work? Do I want to keep a constant voltage and have the current variable as I dim the switch? Is there a cheaper/better/easier way to do this than my current plan?

• You want to use PWM for this. You really, really do. Feb 3, 2015 at 4:54
• What are the voltage and current requirements of the array? Feb 3, 2015 at 14:09
• Are you trying to keep the existing wall dimmer or replace it with something? For some reason this question is attracting poor answers .. Feb 3, 2015 at 17:19
• @pjc50 question updated, I am trying to swap out with as little effort as possible an existing Halogen system. Feb 3, 2015 at 17:46

Wikipedia has some good examples about dimming. For as simple solution as possible (by electrical terms) I would use a transformer, full wave DC bridge and a thyristor. Again, wikipedia has a great picture of that

Note that thyristor dimmers usually make some radio frequency noise but as I see it, this is one of the simplest AC dimmers.

And although you would like to keep out from MCUs, at least think about them. If the thyristor-stuff goes over your head, try to use MCUs. You will find them to be very useful for your future projects.

Here you can look for better understanding:

• It would help if you edited some useful information into your answers. Link only answers are discouraged. Feb 3, 2015 at 8:24
• @David: Sorry for that, and thank you very much for your direction. Feb 3, 2015 at 10:14
• @Olltsu: You can go for PWM option. If you use traic based Dimming for LED then it may be flicker. you have to use proper firing angle for dimming the LED. Feb 3, 2015 at 10:16

I'll take a stab. Cheap and quick, definitely not what I would do, as I am not a power electronics pro, nor an electrician by any means. If you use this you are accepting inordinate amounts of risk.

simulate this circuit – Schematic created using CircuitLab

If you're up for something simple, just source an ACDC supply module. Something like this might do it.