Need help designing a dual PSU - Page 1
Forum section: electronics / projects

author: ElectronSurf
author_rank: Regular Contributor
timestamp: September 07, 2024, 11:01:02 am
content: Hello I have found a massive audio transformer and I'd like to build a dual PSU with it. Having built a PSU before with "floating op amps supply" technique, I have a lead where to start.I can build two independent supplies and then wire them in series at the output, the problem is that I want to add parallel and tracking feature to it and I don't have slightest idea how to approach it.The other problem is the heat dissipation, 150W per channel and no tap on the transformer, I'm gonna need a switching per-regulator and that's something I have never done before.I'd appreciate it if you guys can put me in the right direction, keep in mind that I'm not an EE, am just the next door hobbyist.

author: ledtester
author_rank: Super Contributor
timestamp: September 07, 2024, 03:59:06 pm
content: A switching preregulator for a linear supply was mentioned in this recent post:https://www.eevblog.com/forum/beginners/does-this-schematic-make-sense/A simple solution for tracking would be to use a dual gang pot.Update: Found a schematic for the HY3005F which uses two push switches for selecting parallel/series/indep/tracking operation.https://www.eevblog.com/forum/testgear/mastech-hy3005f-3-seriesparallel-switches-imply-non-floating-supply/msg492343/#msg492343It looks like the switches are SK1 and SK2 at the bottom of page 2 of the schematic.

author: ElectronSurf
author_rank: Regular Contributor
timestamp: September 07, 2024, 06:57:06 pm
content: Quote from: ledtester on September 07, 2024, 03:59:06 pmThanks for the links, can you also help me figure out this section please? It's the switches that control the tracking and series parallel, right?

author: ledtester
author_rank: Super Contributor
timestamp: September 07, 2024, 09:25:08 pm
content: My reading of the schematic is that SK1 and SK2 each are 4-pole double throw switches.The schematic shows one position of all of the poles (presumably when the switch is not pressed). The little lines are the connecting contacts within the switch. When you press the switch all of those contacts slide up one position.For instance, the schematic shows pin 2 connected to pin 1, 5 connected to 4, 8 to 7 and 11 to 10. In the other position pin 2 is connected to 3, 5 to 6, 8 to 9 and 11 to 12.

author: ElectronSurf
author_rank: Regular Contributor
timestamp: September 07, 2024, 09:49:50 pm
content: Is this diagram correct, did I understand it right?In default position the slave connections are the same as master connections:When SK1 is pressed, PSU goes to series mode:It makes a voltage divider between master's positive and slave's ground and connects it to non-inverting pin of error amplifier and puts two supplies in series by connecting master's ground to slave's positive.When SK1 and SK2 is pressed it goes to parallel mode:Master's positive and negative connects to slave's positive and negative, Now the voltage divider is between positive and negative, Master and slave transistors bases are now connected together, CC amplifier non-inverting input is connected to positive.- What is the job of voltage divider in series and parallel?- Why in parallel mode CC amplifier non-inverting input is connected to positive?Also I found two errors in the schematic, master's base current is not connected to the transistors base:And Slave's voltage adjustment pot middle pin shouldn't be connected directly to the 2.5V voltage reference: