PWM and current control

New project

Making a simple PWM for 12 V DC max. Output will be checked by hall effect IC for max 5 Amps.

A screen will show the user what voltage (PWM pulsewidth) and current (which will be loop checked) it is set to.

The input control will be rotary encoders, for voltage and current.

I will update whenever I am doing something about it.


04 Jan 2011


As I said in my posting on my Battery Charger Notebook, I intended to comment on these measurements of current and voltage since they will be needed in that project. But when I think into it I am not so sure I have any answers yet. The problem being averaging a PWM signal, presumably the ADC will give the full value when the pulse is 'on' and zero when it is 'off'. Whether to do the averaging in software, or use a low pass filter, or some other way I have not thought of yet. Perhaps just the proportion 'on', applied to the full value, is good enough, but this looks more tricky for the voltage across a battery

With regard to charging batteries, it is not clear to me that a steady current, and a pulsed current with the same average value, would have the same effect on the battery. It seems to be taken for granted, but the argument for this assumption is not given.


A lot to think about.

04 Jan 2011

Battery charging often gets over-simplified. Lead-acid are the simplest to charge. Newer types of batter technology often needs to be temperature controlled during charge and discharge cycles. From what I understand, batteries are charged using a constant current up to 70% of their capacity and then the charger produces a constant voltage for the remaining charge. Either way, You would be better off to use an LC filter to filter the output voltage going into the battery and your battery voltage would be sensed at the terminals. You would probably need to do some additional filtering in software (i.e. averaging filter) to get rid of some random spikes. Also, it's very hard to make a constant current source without some inductance (hence the LC filter).

Measuring the PWM waveform (at the source) is somewhat meaningless. Since you already know the duty cycle in your program, there is no need to measure it.

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