120v led lamp

Question

Hi,

Ive just started hacking electronics lately, thanks to Jeremy Blum book and tutorials!

My desk lamp fluorescent bulb gave up on me and i wanted to replace the bulb with some white LEDs. So i took appart the lamp and found a circuit board and im not sure what it is for. The fluorescent bulb is rated 120V and i tought it was directly hooked to AC? is this board an AC to DC converter?

Heres some pictures (The side with the fuse is the 120v AC in) :

20141030083725 - HostingPics.net - Hébergement d'images gratuit

20141030083741 - HostingPics.net - Hébergement d'images gratuit

20141030083754 - HostingPics.net - Hébergement d'images gratuit

20141030083813 - HostingPics.net - Hébergement d'images gratuit

So my plan is to enclose a AC to DC converter to a potentiometer that would feed current to around 20 white LEDs(maybe those MCL034SWC-YH1MCL034SWC-YH1. This is my main light source in that room so i would like it to be very bright, but dimmable.
Thanks!

Feel free to recommend me stuff!

supper_slash · Accepted Answer

Looks OK, but, in my circuit, the transformer wont work for 12v. You see you will loose some in the rectifier bridge, and the 7812 will not be able to hold the 12v output. You can drop the 7812 down to 9v version, supplying 9v to the led's. Or find a transformer around 14+ volts. As for the PWM, I think it is more efficient. Less loss on the supply Everything else looks good. NOTE: you can buy a "wall wart" type power supply ready made, that should work, than u just need to do the PWM. But there would be no fun in that. I like building stuff myself, but it is an option.

supper_slash · Answer

Electronic Ballasts: The electronic ballasts use semiconductors to limit power to a fluorescent lamp. First the ballast rectifies the AC power, then it chops it to make a high frequency for improved efficiency. The ballast can more precisely control power than a magnetic ballast but does have a number of problems. That is the circuit you have there. You can use a simpler diode- resistor combo to cut the voltage down for the led's, but its not efficient, and in my opinion dangerous, Because of the fact that it would be direct mains connection. I don't like this type of setup, i like isolation between any of my circuitry, and the mains, but that's just me. I would look to PMW to drive the led's, but that may be too much for your project. If you want a simple diagram, here is one using a Transformer, it may need some customizing for your led's, but it should be a starter. The transformer in the diagram isolates the mains for me in this circuit. Let me know exactly what your looking for. Someone else may be able to chime in if your looking for a switching power supply.As I am not too familiar with them. If you can maybe calculate the led stats, so we could know the Amperes, and voltage limitations for your circuit. That would be helpful.

supper_slash · Answer

You can use that chip, i have used a "mic502yn" before. There is the 555 timer, you can use, or i prefer going old school, and using an op amp. Or, rather four. But your space is limited so mabe a mic502ym with a transistor or fet would be fine I have a schematic of the op-amp PWM circuit if you would like.

120v led lamp

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