Hi there Mr. Timer.

I was wondering what you would recommend to PWM a 20W Led.
Specs are 12V at around 1.7A.

Need something as simple as possible, to make the circuit small. Like to drive a logic level HEXFET used in mobo's...I will use a high current one to make the circuit as feasible as possible.

Brilliance control need to be 20% to 100%. Power supply will be 12V.

I know I shud have gone thru the database. I need to make this quick. No time for trial runs. So I hope you wud take some time to just post a schema that I could make in one go.

 

Ouch..
U just beat Bill by a pic..

 

Sorry, I was deleting it as you were posting. It didn't have all of what you needed.. the 20-100% control.



BUT the 10f204 does have an ADC, so you could add a POT to it for the pwm control.

Here is the app note:

http://ww1.microchip.com/downloads/en/DeviceDoc/51551a.pdf

 

It is not as simple I thought ..it uses another chip isn't it.

Retched...u must be mistaken...it does not use a FET.

But this is handy to make backlit. Is this thing possible to add any no. of LED's

 

I was trying to delete it before you read it.

You can use a 10f204 for the job.

You would need to add a MOSFET, and a POT to adjust PWM duty-cycle for dimming.

 

If the spec is important then a LM393 comparator/555 would be how I do it. The 100% PWM spec is the definer in this case.

LEDs, 555s, Flashers, and Light Chasers

Chapter 5 - The 555 and PWM

The popular schematic will not hit 100%, but the 555 can drive the MOSFET directly with a 4.7Ω resistor on the gate.

555 PWM Oscillator

 

Hey Bill...
I Stole ur schematic idea to make my PWM.
Made the circuit and blew a 1W 3.7V LED, was in such a hurry that I never realize that I had 12V applied. The Led Flashed a couple of times and died. I too was blinded for a while .

Finally realized the hiccup, I do not need to flash the led, just dim it. So replaced the C1 cap with a 0.22uf and Viola.
I can get from real dim to max or DC or something.
Measured the frequency to make sure it was pulsing.

I omitted every component from the output. Instead used a 100Ω R with a logic FET. It drives a 20W led at 12V perfectly @ 555 Hz .....(555 Hmmmmm!!!)

Thanks for the info. Below is a pic for fun

Have a good day.

P.S...the 555Hz part was just a coincidence.......really....what's with you and 555..HUH!!

 

Sorry, I was deleting it as you were posting. It didn't have all of what you needed.. the 20-100% control.



BUT the 10f204 does have an ADC, so you could add a POT to it for the pwm control.

Here is the app note:

http://ww1.microchip.com/downloads/en/DeviceDoc/51551a.pdf

RM, can u please find me these components...I want to make one...real big one. pls reply

 

Your LED, is it a 1W model?

 

The test was with a 1W. Actual load LED is 12V, 20W one.

 

The test was with a 1W. Actual load LED is 12V, 20W one.

Is it working properly now?

 

Is it working properly now?

U betcha!!!!!. It's in a friends kitchen cabinet or something.

 

How much current? A 12V 20W LED (which, BTW, doesn't really exist, this LED has a dropping resistor or circuitry) would use about 1.7A.

Even high power LEDs use the standard dropping voltages, if they are components and not circuits.

 

Sorry my mistake it is 20W and I am using 12V adapter which he has on hand .