[Elecraft] Homebrew power supply question.

[Don Brown]

Hi

The problem with adjustable high current linear supplies is the heat in =
the pass transistors. If you are willing to limit the amount of =
adjustability you could combine the two circuits and the LM317 would =
allow you to adjust the voltage. However if you want to adjust the =
supply to a low voltage and still draw high current then it will require =
many pass transistors and a massive heatsink. If you only want to adjust =
a few volts say from a low of 10 to a high of 15 then you should be OK =
with the combined circuits. If you were to build a supply with a 25 volt =
raw supply feeding the regulator and the output is at 2 volts and you =
are drawing 30 amps then the pass transistors will need to dissipate =
almost 700 watts at 10 volts 450 watts and at 15 volts 300 watts. This =
is why switching regulators are more efficient when the currents get =
high.

Don Brown
KD5NDB=20
  ----- Original Message -----=20
  From: Mark - WB4MSD=20
  To: elecraft@mailman.qth.net=20
  Sent: Friday, August 01, 2003 10:08 AM
  Subject: [Elecraft] Homebrew power supply question.




  I am building a homebrew linear power supply for my K2, and need a =
little help with coming up with a design that I like.  I have been =
looking at a power supply at the following website:  =
http://www.mitedu.freeserve.co.uk/Circuits/Power/1230psu.htm    It's =
simple and I think it will do the job, but I would like to make it =
adjustable and still keep it simple.  I have seen some variable power =
supplies using the famous LM317T and LM350T,such as:  =
http://www.uoguelph.ca/~antoon/circ/vps.htm, but they are for low =
current.  My question is, do any of you engineer-types out there in =
Elecraft land think I could incorporate a combination of these two =
circuits by using the design of the aforementioned second power supply =
and adding the high current transistor array of the first power supply?  =
I also plan to add a crowbar protection circuit on the output.

  You may ask, why not just buy one already built.  What fun is that???

  You guys let me know what you think and if you have a better idea.

  =20


  73,
  Mark - WB4MSD
  Grenada, MS


--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment.  Attachments are not allowed.  To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html  ---