Designing a PSU with three different outputs. - Page 1
Forum section: electronics / beginners

author: Sombiefog
author_rank: Newbie
timestamp: June 12, 2019, 07:05:55 am
content: Hi! First time posting hereSo im doing my electrical engingeering degree and wanted to have a side project during my last year.Ive been wanting to combine two PSU units i already have into a singular one.One is a PC PSU the other is a PSU for a laser unit.I have experience in PCB production, drawing and schematics. But i cant get a good wrap around power electronics.So i want to design circuitry wich takes AC 230V mains and turns it into three DC outputs.Output 1: 19.5V, ~9AOutput 2: 12V, 8AOutput 3: 4.5V, 15AThe power has to travel accross a 20m powercable and is connected to the main network.Does anyone have any tips to get me started?Any pointers? (Buck, flyback? / wich chips? / How do i get the right transformers?)Ive been searching many different websites and programs but all seem to be obsolete.

author: soldar
author_rank: Super Contributor
timestamp: June 12, 2019, 07:43:53 am
content: You want to design and build one single unit to give you those outputs? That is a tall order. It can be compared to a computer PSU and you could probably modify one to do what you need but if you just want to cover a need then I would buy something commercially available.

author: Sombiefog
author_rank: Newbie
timestamp: June 12, 2019, 08:02:47 am
content: It is indeed a tall order.Im just wondering if somone had tips / pointers for where to start.The software which makes examplecircuitry for you is all outdated.I know there are commercial products out there which i can use.But i know this forum has the potential to help me!Ive attached an image of the PSU for the laser. This gives two of the outputs (O2, O3)Thanks

author: DannyTheGhost
author_rank: Contributor
timestamp: June 13, 2019, 09:31:24 am
content: If you want to design your own PSU, you should decide several things: topology, estimated efficiency (active or passive cooling etc.), even which outputs will be regulated and which are not.For almost 400W PSU flyback would be too bigWhen working with mains voltages you also will need isolated outputBut, if you think you have not that specific requirements for PSU, better to think about getting multiple commercial PSU for each voltage, because time is money, and PSUs not that easy to design and make

author: larsdenmark
author_rank: Regular Contributor
timestamp: June 13, 2019, 10:39:23 am
content: You'll need a cable with some thick leads in order to send 15 A through it 20 metres away. If your leads are too thin the cable will melt.And yes, making your own PSU seems difficult at best and you may start a fire in the process if you are doing it wrong.

author: Jwillis
author_rank: Super Contributor
timestamp: June 14, 2019, 07:35:41 am
content: Linear for the amount of current you require would just be to bulky.Go Switch Mode Power Supply .They look difficult but really they aren't.Complex yes but most of what you see in a typical SMPS is filtering.Since you have fixed outputs,the most difficult part would be designing the transformer.As for the distance of your power cable .I would try to put your DC PSU as close to the load as possible and extend the AC source cable.A 100 ft 10 gauge cable with AC would power that supply easily.Where as just for the 4.5 volt 19 amp DC would require a minimum wire gauge of AWG 4 over 65 feet or 20 meters.