Power supply output transistors - Page 1
Forum section: electronics / beginners

author: multime
author_rank: Regular Contributor
timestamp: April 22, 2024, 12:27:51 pm
content: Just wondering if i could get away with using two of these transistors TIP35C TO218 package, mounted on thermal pads with screw through there mounting hole and also be under a spring clip to help ensure good contact with heatsink. This is for a power supply 0-30v a 2 x 15v 300va toroidal transformer will be used and its windings will be switched via a relay to be in parallel or series, the switching will be automatic and occur at around 13/14v. So the output current up to this voltage could be 16/17 amp. The heatsink to be used is a fan cooled Fischer product with a rating of 0.3 c/wI have been going to build a power supply since about 2 years or more ago but apart from having to much to do i couldn't settle on a design i liked. I had help on here about various ways to go but now i have chosen to use a obsolete Motorola voltage and current regulator MC1466L or MC1566L.

author: Terry Bites
author_rank: Super Contributor
timestamp: April 22, 2024, 01:13:26 pm
content: Say you set the output to 30V@17A.If your raw DC is 40V, then Pd is 17*(40-30)=170WIf your output is say 1V@17A then that will rise to over 650W!TIP35s max Pd is 125W and that’s assuming you can keep Tj somewhat under 150'C. More like 100'C tops.That will need seriously deep sinkage and ferocious fanny action.www.ppi-uk.com/heat-sink-calculator/A buck pre-regulator tracking a above the dropout voltage for the linear reg will save you a heap of expensive hardware.It will make for a much more robust and reliable PSU. TIP35s are only a couple of bucks a piece, use more of them to help stay cool.You've just saved on a monster fan and heatsink so why not push the boat out?Consider modding the circuit to use MOSFETsWatch Dave's series on LAB PSU design

author: multime
author_rank: Regular Contributor
timestamp: April 22, 2024, 01:40:05 pm
content: I think i have about 6 i will use them. I am not under standing "buck pre-regulator" i have heard the tern buck boost but never read anything about it. I did make a supply using one or two mosfets from a design in "Everyday practical electronics" but from what read at the time was that mosfets prefer to be fully on, i now the supply was problematic. Will take a look at the youtube link

author: xavier60
author_rank: Super Contributor
timestamp: April 22, 2024, 01:44:23 pm
content: For my 30V 20A bench PSU, I used a single PSMN020-150W,127 MOSFET with a pre-regulator maintaining 3V across it.

author: multime
author_rank: Regular Contributor
timestamp: April 22, 2024, 03:15:27 pm
content: Is your power supply 0-30v or a steady 30v

author: xavier60
author_rank: Super Contributor
timestamp: April 22, 2024, 03:46:35 pm
content: Quote from: multime on April 22, 2024, 03:15:27 pmIts zero to 30V.

author: multime
author_rank: Regular Contributor
timestamp: April 22, 2024, 09:14:42 pm
content: xavier60Does the output go all the way down to zero on your supply if so can you upload the circuit i would like to see the pre-regulator i have never come across them.

author: xavier60
author_rank: Super Contributor
timestamp: April 22, 2024, 10:23:33 pm
content: Quote from: multime on April 22, 2024, 09:14:42 pmYes.At this point I might not be able to help any further. I have attached just the core part of the linear regulator. It's a rather complex Harrison style design where everything is referenced to the Plus output terminal. It is microcontroller controlled via more opamp interface circuitry, not shown.What I was calling a pre-regulator is actually a hand-made 600W offline SMPS. I'll see if I find a photo to attach later.Simpler solutions need to be found.

author: multime
author_rank: Regular Contributor
timestamp: April 23, 2024, 09:59:33 am
content: xavier60Thats ok i was just curious. thanks for the pics. Just the word microcontroller has sent me running for the hills.

author: xavier60
author_rank: Super Contributor
timestamp: April 23, 2024, 10:26:31 am
content: This project happened near to 6 years ago.This is a version I had drawn that's simply driven by Pots, for anyone wanting to experiment with it.There may be no simple way of implementing a simple linear regulator that also works properly.The other option is the BJT design I used in a 5A PSU which may be able to be beefed up with more output transistors.How many, I can't say for certain, at least 4 with a pre-regulator.https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: April 23, 2024, 05:19:51 pm
content: Quote from: xavier60 on April 22, 2024, 10:23:33 pmDid you ever publish the full schematic + code for your own "Harrison style" power supply?

author: xavier60
author_rank: Super Contributor
timestamp: April 23, 2024, 10:33:45 pm
content: Quote from: LooseJunkHater on April 23, 2024, 05:19:51 pmNo, I didn't document it very well.