Edward Cooper wrote:
> that subject isn't very informative!  My problem is that
> I'm using the PWM output to control the rate of charge
> of some batteries and I'm monitoring the current into the
> batteries by measuring the voltage across a 1/2 Ohm resistor
> is series with the batts, the problem is the PWM output
> is controlling the current by high speed switching and
> is interfering greatly with the numbers on the A2D input,
> I've tried basically filtering it out using diodes and
> caps but it doesn't work well and I have to use a long
> median average routine from many samples to get half
> decent numbers for the current flow.


...proper grounding and shielding again...

Why not use STM VIPer or similar switch mode power supply
regulators. Adjust them to a slightly lower voltage than
needed.
Let PIC measure
- output voltage,
- consumed current using extra transformer in series
with the main transformer
Let PIC regulate output by changing opto feedback

It's not easy to beat VIPer(SWITCHING FREQUENCY
UP TO 200KHZ) with plain PIC PWM system, especially
in safety considerations when working from mains.

CAREFULLY FOLLOW LAYOUT CONSIDERATIONS.
As example from VIPer50 datasheet:
--------------------------------------
LAYOUT CONSIDERATIONS
Some simple rules insure a correct running of
switching power supplies. They may be classified
into two categories:
- To minimise power loops: the way the switched
power current must be carefully analysed and
the corresponding paths must present the
smallest inner loop area as possible. This
avoids radiated EMC noises, conducted EMC
noises by magnetic coupling, and provides a
better efficiency by eliminating parasitic
inductances, especially on secondary side.
- To use different tracks for low level signals and
power ones. The interferences due to a mixing
of signal and power may result in instabilities
and/or anomalous behaviour of the device in
case of violent power surge (Input
overvoltages,output short circuits...).
In case of VIPer, these rules apply as shown on
figure 22. The loops C1-T1-U1, C5-D2-T1,
C7-D1-T1 must be minimised. C6 must be as
close as possible from T1. The signal
components C2, ISO1, C3 and C4 are using a
dedicated track to be connected directly to the
source of the device.
---------------------------------------

Good Luck.

Mike.

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