[ARC5] Cold filament protection

[Brian Clarke]

Hello Wayne,
While the 317 is tempting because of the low component count, when I
was teaching tech students, I got the students to build their own test
bench PSUs, with a circuit using two 317s in series - one as CV and
the other, upstream of the CV one, as a current limiter. The 723 is
the ideal device because it contains CV and current limiting, but the
component count is far higher than the dual 317 design. 
In the tech student test bench PSU design, I recommended heatsinks on
both 317s because the students' applications could not be predicted.
For the startup time of your PRC-25, you may not even need a heatsink
on the current limiting 317.
73 de Brian VK2GCE.

On Sat, 17 Mar 2018 21:30:58 -0400, you said:

For my PRC-25 and two PRC-77's I built rechargeable battery packs
using four 18650 lithium batteries.  For the PRC-25 filament power I
used an 317 IC regulator, with a switch to turn it off and prevent
battery drain.  I did not know about the surge protection feature. 
I suppose I could change the 317 circuit to slightly lower the
filament voltage. 
  
By the way, the dial light in those sets uses a lower voltage bulb and
drives the heck out of it to get enough light. 
  
Wayne
-------------------------
Email sent using Optus Webmail
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20180318/718d98c0/attachment.html>