Hi all,

follow-up from the diode question

I'd like to add a PIC and 8 x 2 LCD to this PSU to display Vout
and Iout. Measuring Vout is easy enough, but what about I out ?

The two simplest options appear to be a sense resistor in either
the (a) 0V or (b) Vout line

(a) would be the easier, using a PIC analogue pin, with probably
a DC amp to improve the resolution. But the load will not see a
true ground, which could be a problem if it shares a common chassis/
mains ground with the PSU. Mains earth will go to the PSU chassis
but I don't necessarily have to connect 0V to it as well

(b) is said to be more accurate but needs more circuitry, being a
high-side differential. It does measure the real Iout however

Questions -

If this is a variable 0-35V 5A supply, what value would you make
the sense resistor ? For example to get 5mA resolution (1000th the
full Iout, or ~1 bit of ADC)

If I were to put the sense resistor in the Vout line (my academic
preference) could I have a pointer to a differential circuit that's
compatible with a PIC ? I note that there are many high-side battery
monitor ICs, none of which I have. If there's something that could
be knocked up with a reasonable-quality op-amp that'd be peachy

TIA

Joe
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