Maker Pro
Maker Pro

Additional pass through transistor or bigger reg?

Balrock

Mar 1, 2012
39
Joined
Mar 1, 2012
Messages
39
I have been moving forward with my Bench PSU project and had a look today at increasing its current output. My design (still in breadboard stage) uses LM317 and LM337 regulators so it can provide about 1.5 amp. I was looking at increasing this to around 3 amp.

One option I have looked at is using the same regulators with the addition of pass through "power" transistors. The other option is to use higher rated regulators. What are the pros and cons of each approach.

Thanks for any help given, Paul
 

davenn

Moderator
Sep 5, 2009
14,039
Joined
Sep 5, 2009
Messages
14,039
Hi Paul
The LM338 will happily do up to 5 Amps, dont forget to heatsink it.
messing around with lower rated regulator will work well its just a heck of a lot more work and higher component count.
There's no point with pass transistors unless you are wanting over 5Amps, why complicate things more ?? :)

Dave
 

Balrock

Mar 1, 2012
39
Joined
Mar 1, 2012
Messages
39
Hi Dave. Thanks for the quick reply. Yes I looked at the LM338 but they don't make a negative version of it as my PSU is Dual Rail.

However, I am using 2 x transformers wired together (as I got them cheap) in place of one single unit so would I be correct in saying that if I separate (isolate) and use one transformer per LM338 rail I could wire the + output of the second LM338 to GND (0v) of the first and I would get a dual rail + GND - type configuration.

I hope that made sense!
 

davenn

Moderator
Sep 5, 2009
14,039
Joined
Sep 5, 2009
Messages
14,039
Hi Dave. Thanks for the quick reply. Yes I looked at the LM338 but they don't make a negative version of it as my PSU is Dual Rail.

However, I am using 2 x transformers wired together (as I got them cheap) in place of one single unit so would I be correct in saying that if I separate (isolate) and use one transformer per LM338 rail I could wire the + output of the second LM338 to GND (0v) of the first and I would get a dual rail + GND - type configuration.

I hope that made sense!

ahhhh ok, you didnt state anything about a split rail supply in your first post ;)

Dave
 

davenn

Moderator
Sep 5, 2009
14,039
Joined
Sep 5, 2009
Messages
14,039
OK here's one example along the lines of what you were thinking
NOTE there is NO connection between the secondaries of the transformer

attachment.php


this came from the www site, down the page a little way .....
http://www.tcaas.btinternet.co.uk/jlhesl.htm

cheers
Dave
 

Attachments

  • Dual rail LM338 use.gif
    Dual rail LM338 use.gif
    12.6 KB · Views: 4,047

alfa88

Dec 1, 2010
349
Joined
Dec 1, 2010
Messages
349
Take a look at my project log. I just posted it a couple of days ago. It uses 2- lm338s. As long as the 2 secondaries are not connected to each other; who needs a negative regulator? I might have gone a little overboard on the heatsinks but that's what I had laying around .
 

davenn

Moderator
Sep 5, 2009
14,039
Joined
Sep 5, 2009
Messages
14,039
Take a look at my project log. I just posted it a couple of days ago. It uses 2- lm338s. As long as the 2 secondaries are not connected to each other; who needs a negative regulator? I might have gone a little overboard on the heatsinks but that's what I had laying around .

yup thats what the circuit does that I posted before your post lol ;)

Dave
 

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
The bridge rectifiers must be connected correctly. It would be better to rotate the diode symbol a quarter turn to the left.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
The bridge rectifiers must be connected correctly. It would be better to rotate the diode symbol a quarter turn to the left.

Well spotted.
 

Balrock

Mar 1, 2012
39
Joined
Mar 1, 2012
Messages
39
Thanks all! I love this forum! What sweet headache relief it brings :D

ahhhh ok, you didnt state anything about a split rail supply in your first post ;)

Dave

Sorry Dave, but in my defense I did quote "uses LM317 and LM337 regulators" ;)

I will forge ahead to my next tangled web of confusion. Thanks again guys.

"NOTE there is NO connection between the secondaries of the transformer" is ok for me Dave as I am actually using 2 smaller transformers anyway.
 
Last edited:

davenn

Moderator
Sep 5, 2009
14,039
Joined
Sep 5, 2009
Messages
14,039
Thanks all! I love this forum! What sweet headache relief it brings :D



Sorry Dave, but in my defense I did quote "uses LM317 and LM337 regulators" ;)

I will forge ahead to my next tangled web of confusion. Thanks again guys.

"NOTE there is NO connection between the secondaries of the transformer" is ok for me Dave as I am actually using 2 smaller transformers anyway.

yeah till i googled the LM337 I didnt realise it was a neg rail regulator .... never had the need to use one lol

D
 
Last edited:
Top