Bridge rectifier and a MOSFET as PWM for an AC Light Dimmer

[vicbsee]

I am interested in learning how to use a MOSFET and a Bridge Rectifier to control lights using PWM for incandescent loads. So far, I believe that it can be done, not sure how.

Any suggestions?

Thank you

Victor

vicbsee@yahoo.com

 

[Tahmid]

Hi,
Incandescent loads, I think, should be able to be operated at DC voltages as well. I have lighted many incandescent lamps before with DC 280-300V.
So for dimming, convert the AC to DC with the bridge rectifier, then use the MOSFET for PWM along with the PWM controller with the incandescent lamp as load.
Hope this helped.
Tahmid.

 

[causalitist]

Re: Bridge rectifier and a MOSFET as PWM for an AC Light Dim

nonono.. you need two mosfets, both in series, but also both highside(above load)... same gate signal goes to both with gate signal return tapping between the fets.... ahh.. i saw it on MAXIM's (spelling?) site.

the output is the same sine wave but chopped up into many on/off square waves if you zoom in (aka square freq is high, of course)... didnt mess with it much, thought it was neat and planned to... was suprised no highside driver was needed.
i think i simulated it on LTspice, lemme look.

FOUND IT.. AN HOUR LATER.

so if you chop the sine with a much higher freq square, the effective Vrms will be lower, the lower the duty cycle you use... i will assume you do not need to make this dc for your load... you may however need a tiny LC filter(depends how high of freq u use) to get rid of any square and get a lower amplitude sine. im curious of your results, i havent had time to mess with it. i hope you have LTspice, its free, and kicks ass ... and required to simulate crap i sent.