A serious power supply - Page 1
Forum section: electronics / beginners

author: nick.sek
author_rank: Regular Contributor
timestamp: May 07, 2012, 12:37:37 am
content: Does any one have a link to a really solid schematic for a variable linear power supply? As I want to build my own or a least get a very serious kit. I'm looking for something with relays to engage the higher voltages as well as constant current abilities. If any one could post a link I would be extremely grateful.ThanksNick

author: BravoV
author_rank: Super Contributor
timestamp: May 07, 2012, 12:54:16 am
content: Though still in early stage, just watch closely this thread here ->https://www.eevblog.com/forum/projects-designs-and-technical-stuff/general-purpose-power-supply-design-7488/

author: Unknown
author_rank: Unknown
timestamp: May 07, 2012, 01:01:31 am
content: Define 'higher voltages'.This ELV design(good opportunity to practice your German reading skills) uses a voltage doubler to reduce dissipation at lower voltages. Another design istap switching. They also sell kits, no idea what shipping would be like to whatever country you live in. Both are solid designs with variable voltage and current limits. HP published a power supply design handbook (AN90B), not sure if it discussed tap switching, but it discussed many other power supply principles.Amspire's design is also very interesting, I almost forgot about it since that thread wasn't updated for a whole week. Less conventional, and aimed at lower currents. I wouldn't start building yet if you don't have a solid understanding of this topic, and it will be a while (if ever) for kits to become available.

author: free_electron
author_rank: Super Contributor
timestamp: May 07, 2012, 01:12:44 am
content: why relays for switching? the really good ones use a thyristor controlled bridge to do this ... if you want to see a really good schematic go get the servicemanual for the E3610 power supply of Agilent. they have it onine. that is a proven design.

author: david77
author_rank: Frequent Contributor
timestamp: May 07, 2012, 01:17:09 am
content: Have a look in this ongoing thread:https://www.eevblog.com/forum/general-chat/lm350-power-supply/msg109454/#new

author: TerminalJack505
author_rank: Super Contributor
timestamp: May 07, 2012, 01:19:44 am
content: Quote from: free_electron on May 07, 2012, 01:12:44 amOne reason is that you are going to lose at least 2V through each of those bridges.

author: free_electron
author_rank: Super Contributor
timestamp: May 07, 2012, 01:58:43 am
content: You lose 2 volts in your classic rectifier anyway. Replace two diodes with two thyristors and your losses remain the same.If loss is so important then use mosfet to do the switching. almost zero loss. this is what the higher power agilents do.besides, the thyristor trick has another advantage ( besides the clickless switching ) you can play with the phase angle of iginiting the thyristors and use this as a tracking preregulator... this reduces the heat generated in the pass transistors substantially as you have to 'burn-off' les voltage. it is especially efficient at high current - low voltage settings.

author: TerminalJack505
author_rank: Super Contributor
timestamp: May 07, 2012, 02:13:57 am
content: Ah, I assumed there would be a bridge for each tap. I'll have to check out the design.

author: free_electron
author_rank: Super Contributor
timestamp: May 07, 2012, 05:11:20 am
content: nope. they use the thyristors in the positive chain. the 'bridge' is made with 2 diodes and 4 thyristors. there are variations where they use 2 diodes and 2 triacs.transformer has a secondary with a center tap.One end has 2 diodes , center tap has a triac , and the other end has a triac too. they just apply fase regulation to the triac on the center tap for low range. if you go higher they stop the triac on the center tap and start doing fase chopping on the triac at the end.

author: Zero999
author_rank: Super Contributor
timestamp: May 07, 2012, 08:38:29 am
content: One advantage of a relay is it can be used with a twin secondary transformer to switch from series to parallel so double the current can be drawn, at lower supply voltages. This of course means the power dissipation would be higher but it provides more flexibility.

author: AlphZeta
author_rank: Regular Contributor
timestamp: May 07, 2012, 05:20:14 pm
content: I just built one myself, including the relay on the input side. This power supply uses an LM338 and can deliver 5A from 1.25 to 20+ volts. If you are interested, you can check out my build log here:http://www.kerrywong.com/2012/04/30/5a-lab-power-supply-with-digital-readout/

author: nick.sek
author_rank: Regular Contributor
timestamp: May 07, 2012, 07:33:04 pm
content: Thanks everybody for the input. I'll let you guys know where I stand in a couple of weeks on designs and building!