Is single +ve output from dual power supply safe - Page 1
Forum section: electronics / beginners

author: RobtP
author_rank: Contributor
timestamp: November 10, 2024, 07:23:51 pm
content: It feels like this is a very simplistic question but I haven't been able to get an answer with internet searches, possibly because I haven't got the search terms right.I made a dual output power supply, DC +/- 20v (ish) using 15v-0v-0v-15v, 50va transformer - rectified, smoothed etc for a project yet to build.I would like to make a chip-amp, initially powered with the power supply I have, using the +20v output and gnd, as a single output supply, not connecting the -20v output to anything.Is this a bad idea? I'm pretty sure it would be ok but I can conceive there could be problems caused by only half the circuit and one side of the transformer in use. Would it be better to hold off until I get hold of a more suitable power supply?

author: Andy Chee
author_rank: Super Contributor
timestamp: November 10, 2024, 07:31:43 pm
content: If originally designed for dual/bipolar supply, the schematic of the chip-amp may need to be modified to operate from single rail supply.Do you have a proposed chip-amp schematic?On another matter, I'm not clear on why you are reluctant to use -20V? If you've made it, use it!

author: Psi
author_rank: Super Contributor
timestamp: November 10, 2024, 08:13:54 pm
content: From the perspective of the power supply it's fine to only use one side, with two minor caviets for some power supplies.On some power supplies they have a temp sensor on only one of the heatsinks, usually the positive side. So if you only use the negative side the over temp protection doesn't function.Oh, and if it's a 50W power supply and you only use one side, don't expect 50W, since you're only using one of the windings. Probably get more than 25w since the inactive side isn't making heat so the active side can handle more power, but not 50w

author: TimFox
author_rank: Super Contributor
timestamp: November 10, 2024, 08:20:56 pm
content: For the non-switching power supply you mentioned, having no load on the negative supply (two diodes and a capacitor) will have very little effect on the positive supply.Years ago, I remember some higher-power multiple-output switching supplies that required a minimum load on at least one output for the others to function properly.

author: RobtP
author_rank: Contributor
timestamp: November 10, 2024, 08:34:03 pm
content: Quote from: Andy Chee on November 10, 2024, 07:31:43 pmThe chip is a (genuine!) TDA7375a. It's a single supply, max 18v chip (won't be a problem to lose a couple of volts), link to datasheet is below if you want to view it and prove me wrong. The schematic I'm using is the one for double bridge circuit, fig. 4 on the datasheet.This is a temporary measure, will get a more suitable power supply if it seems worthwhile once I build it (working, volume, sound quality). The one I have will be put to full use at some point.https://www.st.com/en/automotive-infotainment-and-telematics/tda7375av.html

author: RobtP
author_rank: Contributor
timestamp: November 10, 2024, 08:40:23 pm
content: Quote from: Psi on November 10, 2024, 08:13:54 pmGood point about the loss of power, I should have thought of that but I don't think it'll matter, just might make the amp clip a little sooner than it might have.This is a temporary measure, will get a more suitable power supply if it seems worthwhile once I build it (working, volume, sound quality).

author: Andy Chee
author_rank: Super Contributor
timestamp: November 10, 2024, 08:50:54 pm
content: Quote from: RobtP on November 10, 2024, 08:34:03 pmFrom what I can tell, the TDA7375a does not use a bipolar supply. So why do you need -20V in the first place?Oh! I understand now! Your bipolar supply is for another project, not the TDA7375a.