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Topic: Voltage control with PWM-signal (Read 9358 times) previous topic - next topic

MarkT

I'm sorry I came so late to this thread, it seems to be full of confusion.

PWM is not analog.  You want an analog voltage at high power, you need
either an analog amplifier or an adjustable switch-mode regulator.

PWM is used when the load doesn't require an analog voltage, such as LEDs
where the flickering is averaged by the eye, or motors where the current is
smoothed by the winding inductance so the rectangular voltage waveform
isn't a problem.

Heating isn't an issue, PWM will work fine.

For electrolysis you _need_ an analog voltage so you need to generate one.

Switchmode supplies are by far the most efficient way to do this, so what
is needed is a switchmode circuit with adjustable output voltage.  For low
power loads a simple op-amp low-pass filter circuit will produce analog
at a few 10's of mA typically.

None of the circuits I've seen on this thread make any sense as far as I can see,
as they put a PWM signal directly into a capacitor which will simply store the
supply voltage across the waveform.  Indeed TomGeorge's circuit doesn't even
connect the MOSFET circuit at DC to anything as far as I can see.

For a PWM circuit (heater, motor etc) the load goes between drain and supply
and there's no point measuring the voltage there since you know the duty cycle
already.  You might want to measure the current...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

TomGeorge

Hi.



Quote
I now have the circuit set up like in Tom's diagram pwmreg.jpg (Thank you, Tom!), which was very similar to what I had previously... 
The circuit I supplied IS your circuit. I tidied it up so we could see what you have.

Question... WHAT is the reason for the 1000uF in the output circuit, how is it supposed to work?
What is supposed to be  the load?

Again, the diagram I supplied is your diagram.

Tom.... :)
Everything runs on smoke, let the smoke out, it stops running....

msensor

Hi,
thanks for the replies.
I think that a lot of the confusion stems from my own limited knowledge of electronics. Although I took a fundamentals of electronics course, I'm more or less learning as I try to get these projects to work... always grateful for tips and advise  :)

I'll look into the switchmode supplier; that sounds like good option for the electrolysis. Thanks for the tip.

Tom, I saw a capacitor in other diagrams; I think that's a large part of the reason I included it. I thought the capacitor would smooth out the current and voltage before it gets to the output, but apparently it's not necessary. I've tried it now with and without the capacitor, and it seems lie the capacitor simply reduces the output voltage... without the capacitor, the output voltage is the same as the input voltage.

MarkT, you wrote, "For a PWM circuit (heater, motor etc) the load goes between drain and supply
and there's no point measuring the voltage there...". I belive that I do have the load, the motor in this case, connected in that way. I have a wire going from the drain of the MOSFET to the negative pole of the motor. The psoative pole of the motor is connected to the posative output of the regulated DC power supply (The negative lead from the DC supply goes to the source pin of the MOSFET, which is also connected to the ground). Then I have my digital multimeter set up to measure the voltage supplied to the motor. Doesn't it make sense to measure the voltage at this place, because this is the voltage I am trying to control? I thinking I check voltage I measure with the DMM to verify if the circuit/arduino are properly controlling the voltage. In what other way should I check what the output voltage is?

Marcus

justGene

Hi I'm trying to use the PWM with an RC filter as an analog source.  It cannot be loaded (source hardly any current) it simply loads the output of the filter. :o
Not too sure this is relevant to your issue but it seems to be.
gene

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