DIY Supply.. Trying to learn. any help apreciated..

**lexwalker** · 02-03-2011, 11:02 AM

Re: DIY Supply.. Trying to learn. any help apreciated..

Originally posted by Aalelan

I have started down many paths but what I really want to do it learn what is needed to build a SMPS for all my bench work and HAM radio equipment. I have an old ATX converted that I have used for years but its not going to be able to keep up before too long..

How much current does your equipment require?

Originally posted by Aalelan

I have read tons of forums and DIY/Homebrew sites but I still end up confused, no one seems to do Switch Mode..

That's because SMPS is more complicated than the usual transformer, diodes/rectifier and voltage regulator stuff. You will need the proper coils/inductors/transformers, correct type of capacitors, switching transistors/MOSFETs and special diodes/rectifiers (usually Schottky ones). Thus its rarely used in DIY stuff.

Originally posted by Aalelan

I found a link to http://schmidt-walter.eit.h-da.de/smps_e/smps_e.html and keyed some values in but I dont understand what those transistors are on the Primary side I'm attaching an image of what I put in there to maybe I can get a little help/lesson to get me going with a little more steam, I would really like to get one built and running my stuff so I can say I made that.

That's voltage full swing push-pull configuration (able to drive from full +Vsupply to -Vsupply). If you ever seen a car high power amplifiers using bridge configuration, its almost the same thing.

**Aalelan** · 02-03-2011, 11:18 AM

Re: DIY Supply.. Trying to learn. any help apreciated..

HAM Radio 22A @13.8v
Hobby Charger ~10A
Misc stuff ~5A
Future Amp for HAM ~40A

So total and I know it wont all be on full all the time is ~77A so thats why I was shooting for around 80+ amps

I have tons of old HP server power supplies that I can gut for heatsinks Rectifiers and Schottky diodes, and I'm no stranger to Digikey and Mouser.

I have done through hole and SMD work via kits for projects so I have some solder skills, and I'm not afraid to etch my own boards.. I have used cadsoft and made a few small things.

This is just a new dimention I have not dove into and I really want to learn and understand it..

**Th3_uN1Qu3** · 02-03-2011, 11:28 AM

Re: DIY Supply.. Trying to learn. any help apreciated..

I have a calculator spreadsheet but for now it only deals with 2 transistor forward. Anyway, the equations i have used are mostly from "Switching Power Supply Design, third edition". That book will tell you just about everything you need to know. Marty Brown's "Power Supply Cookbook" is also good but it's kinda awkwardly organized. But you will find in there what you didn't find in the other, including one of the most critical topics of SMPS design - control loop compensation.

**Aalelan** · 02-03-2011, 11:52 AM

Re: DIY Supply.. Trying to learn. any help apreciated..

I just found a copy of those two books.. I'm going to start reading, I'm not in a hurry to get this done but the idea of working on it gets me excited. I need a new project to burn some time on..

**Th3_uN1Qu3** · 02-03-2011, 03:11 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

One thing to note is that the wire diameter calculations in those books are WAY overrated. I have a calculator in the spreadsheet attached to the last post in this thread. This will realistically tell you what dissipation you can expect for the specified wire area, length, current and temperature rise.

I can tell you one thing - for 80 amps you will need thick litz wire, so that you can keep the frequency high and number of turns reasonable (skin effect comes into play). I usually run my supplies at 100kHz effective frequency. For a half or full bridge that means you set the oscillator on the controller at 200kHz. For a forward topology you would set the oscillator at 100kHz. Both topologies are suitable for your power output - you don't see full bridge in PC power supplies rated for 1kW or more, just the double-ended forward converter. It's my favorite topology as well.

Also a full bridge would need a specialized controller, for two transistor forward or half bridge you can grab a controller from almost any old PC PSU you have lying around.

Unfortunately i didn't have time to supply the wire tables for the calculator as well so grab 'em off the internet. Oh and one more thing. If you go with the 2 transistor forward converter i'd suggest you use type 1 compensation ie just a single capacitor. This means your transient response is going to suck, but radio equipment is fairly constant in power draw so i wouldn't worry. Just use a fat capacitor bank and it will take care of things for you.

**370forlife** · 02-03-2011, 03:21 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

Originally posted by Th3_uN1Qu3

you don't see full bridge in PC power supplies rated for 1kW or more, just the double-ended forward converter. It's my favorite topology as well.

Antec HCP1200.

**MXM** · 02-03-2011, 05:35 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

nice thread, hope u make it.

peace

**Aalelan** · 02-03-2011, 06:48 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

Thanks Th3_uN1Qu3 I got your sheet just now and I'm going to take a look at it.. I'm starting to think the science behind all this is going to be a little more than I can grasp but I'm going to make my best swing at it..

Sounds like I better stick to looking at double-ended forward converter for now as if its your favorite I might be better off getting a little help along the way

Lets see how long it takes me to get my head wrapped around this to ask good questions.. I'm also not apposed to taking help in the form of sample schematics if you have some things for me to look at and try to digest..

Thanks!!

AA

**Aalelan** · 02-08-2011, 12:56 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

Well I have made a find: http://www.a-and-t-labs.com/K6_Sw_Amp/index.htm

1KW SMPS 110V mains fed
I just need to figure out how to trim out the voltages I dont need and regulate in 13.8V out only.. they sell the thing as a kit plus they have a BOM and schematic on there site..

if anyone would like to help me gut this down I can do my own board layout and etching..
https://cdn.badcaps-static.com/pdfs/...7321ae22cd.pdf

At least I feel better I have something to start with now.

**smason** · 02-08-2011, 01:16 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

Don't be too surprised when you get it all working and find that you get about S-8 worth of noise on 80 metres.

That's why I still use a big Astron PS for my HF gear. I still get some noise from the cheap switcher wall-warts on some of my other stuff.

**Aalelan** · 02-10-2011, 02:26 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

Has anyone used this site before?

http://www.poweresim.com/

AA

**Th3_uN1Qu3** · 02-10-2011, 03:16 PM

Re: DIY Supply.. Trying to learn. any help apreciated..

Haven't used it. But honestly, making the transformer is the easy part.

DIY Supply.. Trying to learn. any help apreciated..

DIY Supply.. Trying to learn. any help apreciated..

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