Yep, if you want better performance you will have to pay for it.  I've
been thinking about building another in-house bench supply with a National
simple switcher just to get the experience using them.   Of course, this
is always on the back burner unless the old power supply is fried.


-- Lawrence Lile





"Paul James E." <jamesp@intertex.net>
06/25/2004 04:41 AM


        To:     PICLIST@MITVMA.MIT.EDU
        cc:     llile@SALTONUSA.COM
        Subject:        Re: [EE]: microcontroller based variable voltage regulation, how?



 Lawrence,

 I agree 100% from a regulation standpoint.  But from a noise perspective,
 you'd be hard put to gain the same performance from such inexpensive
 hardware.   We have spent many manhours designing a power supply for a
 system we designed and build.   The noise performance for this system
 is around the -140+ (or should that be minus for lower noise)db range.
 This is not easily achieved by weither a linear type regulator or a
 switching type regulator.  We have achieved a small switching supply that

 has an input range of about 3 VDC to about 18 VDC with an output of
 plus and minus 5 AVDC @ ~200ma (each leg).  And this with a noise figure
 of better than -140db.   Not easily achieved, and not inexpensive, but
 doable.

 But as a practical matter, your design is sufficient for most lab uses
 you will probably run into in general work.   But if you have to have
 a very quiet supply, figure on spending a few more bucks than this.

                                               Regards,

                                                 Jim



> Well a straightforward way to do this is a PIC based power supply.  I
> built some with the following rough outline:
>
> Slew controls (two buttons, one up, one down)
> Power up at 1.2 volts (about as low as it will go anyway
> Range 1.2 to 24 volts at 1 amp
> User interface consists of a digital voltmeter module
> PIC checks the output voltage via a resistor divider and an RC filter
> through analog input
> PIC drives a series pass transistor at regular intervals  - on a timer
> at about 20KHz the PIC decides if the output is too high or too low and
> turns the pass transistor on or off.
>
> Current regulation is crude and simple.  The PIC is powered from the
> same supply as the power supply.  If you short it out, you short out
> the PIC and it reboots and turns off the current.  Crude, Rude, and
> short proof, so far meets my needs.  I was going to build in a current
> foldback feature when I accidentally discovered that this works just
> fine.  If I was going to sell this I would of course include current
> foldback, but this was a quick one-off bench supply to replace the
> other one that fried.
>
> PIC is on a simple 7805 regulator, the rest of the supply is on a 24V
> DC power supply.  The whole thing is in a plastic box from radio shack
> and took an afternoon to put together.  I added a dedicated 5V supply
> from a simple 7805 just for kicks.
>
> I've always built my bench power supply, partly because it galls me to
> pay $200 or $300 for one that doesn't regulate any better than one I
> can build out of spare parts.
>
>
> -- Lawrence Lile
>
>
>
>
>
> John Waters <john_fm_waters@HOTMAIL.COM>
> Sent by: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
> 06/25/2004 12:38 AM
> Please respond to pic microcontroller discussion list
>
>
>         To:     PICLIST@MITVMA.MIT.EDU
>         cc:
>         Subject:        [EE]: microcontroller based variable voltage
>         regulation, how?
>
>
> Hi All,
>
> I want to use my car battery to provide a range of variable d.c. from
> 0-12V,
> but a standard regulator circuit doesn't fulfill the requirement, as I
> want
> the output voltage to be adjustable by software through a
> microcontroller, could someone suggest how to do that?
>
> Thanks in advance!
>
> John
>
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