# My power supply

Discussion in 'Electronic Basics' started by Abstract Dissonance, Feb 3, 2006.

1. ### Abstract DissonanceGuest

I'm working on making a power supply that supplies different fixed regulated
voltages and also a + and - variable voltage (actually all the
configurations I will have are +5, +8, +12, +15, +15 and +24 along with a +
and - variable from 0 to 20 volts).

Now, I also plan on using an LCD to display the voltages and currents for
each(but using one 24x1 LCD).

My question is how can I control for automatic "resolution" for the voltage
meter? like I can use a fet(or maybe an op amp) to detect the voltage but I
need some kinda variable resistor that I can controll with my
microprocessor(which has build in 10bit ADC). I know there are ways to do
this but I'm not exactly sure what I need... I'd like 4 places of accuracy
from uA and mV to A(1.5A max) and V's(25V max).

I also have a fan in my case and I'd like to controll it depending on the
temperature... what device will return the temperature in the case that I
can use with my MCU to control the fan current?

Last thing I'm not to sure on is where to place my on off switch in the
circuit.

right now I have mains->fuse->varistor->filtering->switch->transformer but
it seems that I would want the switch right after the fuse?

Thanks,
Jon

Good Luck!
Rich

3. ### ehsjrGuest

What do you mean by "4 places of accuracy"?

In any event, you seem to be mixing accuracy with resolution.
You need to specify both.

Ed

4. ### Abstract DissonanceGuest

what I what I ment was 4 digits of precision. The accuracy is not a big
problem the voltage should be stable enough so that I can get an accurate
reading by adjusting a trim pot and using my DMM to match it... but it needs
to be somewhat precise.

For example, say I am trying to set 7.43V's on the output but my
measurements only give me a precision of 1V then I can't get that setting
and my reading would be anywhere from 6.43 to 8.43 volts... way to much of a
swing to be of any use.

If say, though when I use my perfect DMM to measure the voltage and its
really 3.43 instead of 7.43 then my accuracy is wrong and I can change
pretty easy(or should be able to by just adjusting a resistor(which would
probably throw off the precision to some degree too though)).

i.e. accuracy corresponds to calibration which should be easy to
accomplish... the precision is much more comlicated and depends on the
components and circuits used. Although I suppose some circuits are better
for accuracy too but it seems that it would be much easier to get adjust for
accuracy than precision.

Jon