Isolated LED Dimmer with external PWM

Projects General Guidance
1
  1. I want to control a PWM generator with a digital potentiometer.
  2. I want to shutdown the PWM circuit if not needed.
  3. I want to isolate the PWM circuit or LED driver.

The PWM generator i want to use is this one:

It accepts 3-20 volts.
Not clear to me is if it can be driven with another voltage then the LED driver like in my circuit.
Cause i did not find a digital isolator with ~12V input.
Also the digital Pot needs 5V.

It would be nice if i can move the digital isolator between the PWM and LED driver circuit.
This would allow me to use a dual-channel isolator instead of the quad and would be cheaper.
But i want to be able to shut down the PWM circuit if not in use like i have it now and
i don't know if thats easy possible cause i was reading that turning of ICs they get destroyed
if they then receive something on there inputs.

I know there is stuff like the PCA9685 (for PWM) and also the ATmega can to PWM
but i want to use the LM 339 for PWM.

The LM393 is a photo detector circuit to get the status of the bistable relay.

LED PWM.png
LED PWM.png1677×773 31.8 KB

2
  1. I want to control a PWM generator with a digital potentiometer.
  2. I want to shutdown the PWM circuit if not needed.
  3. I want to isolate the PWM circuit or LED driver.

All of these sound achievable with a simple Arduino board and very little external hardware whereas the circuit you attached looks overly complicated.

3

As i said i don't want the ATmega to do generate the PWM

4

MrGlasspoole:
As i said i don't want the ATmega to do generate the PWM

May I ask why not ?

5

From what i read is that it takes all the processing power of the ATmega.
I was reading about bit angle modulation that doesn't do it but don't understand how to do it.

6

If you really want a separate chip, you could just use another AVR. You can get an ATtiny85 IC for less than $3. Microcenter even sells a complete Arduino Pro Mini for only $3.99.

Having said that, I agree with UKHeliBob that you can probably just do it all in the ATmega328. The PWM outputs are run by custom circuitry within the chip, so the software isn't dealing with that at all. It's easy enough to do some experimentation and build up a simple prototype to test it out.

--Doug

8

Ok it looks like people talk about two different things but don't explain what they are using.
There is hardware and software PWM and the people who are after bit-angle modulation for efficiency are using software?

So all i need is one ADUM 1200 for isolation like in the new circuit (attachement)
and let the ATmega do the PWM?

dimmer2.png
dimmer2.png1734×859 28.3 KB

9

Bit-angle modulation is a technique for doing PWM in software efficiently. You're better off using hardware PWM if you can.

--Doug