Performance wise, the LM317 current source isn't great, however the reason why I suggested it was firstly the minimal component count, i.e. one resistor and the IC, and the fact that they are pretty rugged devices with over temperature protection etc. (although I wonder if that works OK in constant current mode). Absolute accuracy and stability in this application aren't really important, as long as the caps can be charged within a certain time, then it should be fine.
Mike Rigby-Jones
-----Original Message-----
From: Paul B. Webster VK2BZC [SMTP:paulb@MIDCOAST.COM.AU]
Sent: Thursday, April 06, 2000 10:13 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [OT] Constant-current cap charging
Thomas McGahee wrote:
> See the attached PDF file for a very simple constant current source
> that might work for you.
That or the two-transistor version beat the pants off the LM317 or
constant-current diode suggestions (the latter if only as they are hens
teeth at higher currents, though minimum voltage drop is also higher).
Tom, why must you post PDFs? GIFs inline into the mail much easier so
we can see them straight off in the navigator. Your PDFs appear to
incorporate GIFs, including text, anyway.
Your other suggestion of the transformer - would be far better off
to use the second transformer to power the PIC as well I should think.
I would think though that the space needed to add *any* second
transformer would be better utilised fitting a decent transformer in the
first place - possibly a C-core or toroidal.
--
Cheers,
Paul B.