Universal power supply board - Page 1
Forum section: electronics / projects

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 04, 2019, 12:28:30 am
content: EDIT: Please see latest design in post number 4......I'm building a universal PSU PCB for my projects so I can have a load made and build them differently for whatever I'm making.If I need current limiting I'm thinking of an LT3080 but if I need to limit the current on the negative rail is this the correct setup?I'm happy with the rest of the project and the values are still for sorting.....

author: StillTrying
author_rank: Super Contributor
timestamp: March 04, 2019, 09:25:18 am
content: If you reverse D13 and D14 the +Ve current limit would look correct to me.I don't think there's any way to make a-Vecurrent limit using a +Ve regulator with a center tapped transformer, you'd need 2 separate floating windings and bridges at least.

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 04, 2019, 10:20:18 am
content: Whoops! Re D13 & D14, that was a typo!! I think I swapped them round whilst moving them about :-)My original design started with two sets of diodes and I thought that I might need to take those outputs and have two identical current limiting circuits then connect the pos of one to neg of the other and create the two from that but then I thought I’d just ask as there are a lot of people on here with much more experience than me. I may well do the current limiting with a 78 & 79 then go to the voltage regulation OR back to 8 diodes and use a couple of 78s. I’m trying to make a power supply board that I can have 25 made of and use for virtually anything I need by fitting the right components. Still might go back to 8 diodes.....

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 04, 2019, 08:31:34 pm
content: OK, I've completely redesigned the entire board now. The whole idea is that this is a universal board that I can use to power my projects. I will probably have it made 20+ times and just keep a stock of them. In most cases only a few of the options will be installed. So I might have just the first bank of diodes and the LT3050ET or I might have a positive and negative 12V rail. There is an optional current limiter as well.Can anyone see any obvious issues?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 04, 2019, 08:49:27 pm
content: Using a L7818 for current limitation is really odd, as 18 V over the current setting resistor is really a lot.If at all a LM317 would be suitable, but it has a different pinout.The 3 pins regulator already have a current limit inside, though fixed, but there are a few types to chose from:78Lxx for some 100 mA78Mxx for some 500 mA78xx for some 1000-1500 mA78Sxx for some 2 AFor just protecting a circuit in case of a short or failure, this is often good enough.

author: Kjelt
author_rank: Super Contributor
timestamp: March 04, 2019, 08:55:36 pm
content: Using a 7815 to input the 7805 is quite steep IMO.For each 100mA output you loose 1W in heat.Why not use a smps to drop Vin to about 8V and use that as input for the 7805? If noise is a concern you could put a 7809 in front you have more output voltages at your disposal.

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 04, 2019, 09:25:23 pm
content: Quote from: Kjelt on March 04, 2019, 08:55:36 pmThanks, it’s a universal board so it might be a 9v and 6v or 12v and 6v or something like that. I do accept that 15 to 5 might be pushing it so have the option of the variable. I’ve done 12v to 5v on a similar board before.

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 04, 2019, 09:28:25 pm
content: Quote from: Kleinstein on March 04, 2019, 08:49:27 pmThanks. I was just populating the board which is designed for options. If I only needed 5v I would use a 9v 7809 etcI hadn’t actually realised that there were different 78 series although as I type this I am getting a slight recollection. Maybe it’s my age. Thanks