Circuit diagram for power supply kit - Page 1
Forum section: electronics / projects

author: Dhanushka
author_rank: Regular Contributor
timestamp: June 24, 2019, 05:54:31 pm
content: https://www.ebay.com/itm/0-30V-2mA-3A-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-Short-with-Protection/272492114559?hash=item3f71cbb27f:g:EXAAAOSwa~BYWQ85Can any one give me the circuit diagram for this kit or any other one better than for this according to following specs?0-30V variable output voltage with variable 0-3A currentThanks

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 25, 2019, 04:26:35 am
content: It's some type of buck/boost converter since the max Vcc is 24V but the outout goes to 30V . I don't see any inductors tho, how is that powering 3A if there's no external inductors ?

author: mariush
author_rank: Super Contributor
timestamp: June 25, 2019, 04:54:19 am
content: Pictures in the link are clear enough to draw the schematic yourself.

author: Dhanushka
author_rank: Regular Contributor
timestamp: June 25, 2019, 05:33:46 am
content: Dear lordvader88,The peak value of 24 V is greater than 24 V. Therefore, it has high DC level of greater than 24 V after regulation. Also, it needs a at least 3A transformer for sufficient current of 3A.

author: MosherIV
author_rank: Super Contributor
timestamp: June 25, 2019, 06:29:31 am
content: So you are saying that the kit needs a 24V 3A transformer?Sounds like a linear type. With 24V input V, the psu will struggle to deliver good clean V above 22V under load. 24V transfers are called 24V for a reason - they are designed to deliver 24V under load.Then the regulation of the psu will loose another 2V approximately.Sounds like the suppliers either do not know what they are doing or they hope that buyers are not going to notice the poor high power performance or assume it is an assembly issue.

author: JackJones
author_rank: Regular Contributor
timestamp: June 25, 2019, 06:44:00 am
content: http://www.paulvdiyblogs.net/2015/05/tuning-030v-dc-with-03a-psu-diy-kit.htmlThere's the schematic, along with some improvements made to it.

author: xavier60
author_rank: Super Contributor
timestamp: June 25, 2019, 06:44:11 am
content: It will output 30V or close with little loading.As well as the 24VAC transformer, looks like a heat-sink and fan needs to be added.

author: Zero999
author_rank: Super Contributor
timestamp: June 25, 2019, 07:46:01 am
content: That kit contains some design flaws. At best it'll perform very poorly, at worse, it'll blow up. Here's a thread discussing it in detail.https://www.eevblog.com/forum/beginners/0-30v-0-3a-psu-audiogurus-version/msg2232978/#msg2232978

author: rstofer
author_rank: Super Contributor
timestamp: June 26, 2019, 03:41:55 pm
content: See what happens when it puts out 1V at 3A. This is the mode where the pass transistor dissipates the most heat.Real 30V 3A PSUs are really difficult to get right and $3 isn't likely to be enough. Among other things, the AC transformer should have taps to reduce the rail voltage when the user selects a low output voltage. You really want to minimize the voltage drop across the pass transistor. There's a reason that bench supplies with a couple of 30V 3A outputs and a single 5V 3A output cost a lot of money.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 26, 2019, 04:52:29 pm
content: The kit is well known and not really capable of delivering 30 V / 3 A. It is more suitable for something like 16-18 V and 2 A, using a 18-20 V transformer. With the given parts a 24 V transformer is too high for the OPs. Even with a 24 V transformer and luck with the OPs to survive too high a voltage the maximum voltage would hardly reach 30 V (no load) as the drop out is relatively high and the filter cap is more suitable for 1.5-2 A.The kit also only consists of some part for the power supply: it still needs the case, transformer and heat sink / fan. Though around for a long time already the board layout still seems to be poor old version, with lots of ripple in CC mode.

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 26, 2019, 04:57:24 pm
content: OP just use it for up to a few hundred mili-amps from a smaller transformer, and it would be fine for powering basic stuff on a breadboard.