Interesting reading on SMPS - Page 1
Forum section: electronics / general

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 12, 2014, 10:30:57 pm
content: I found this very interesting and thought id share it here.It's all about SMPS and how they work.I would like to make a 12v 30amp SMPS if any one has any schematics.https://www.dropbox.com/s/hkgp6pi12iyg9jv/SMPS%20AC%20DC%20Reference%20Design%20User%20Guide.pdf

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 16, 2014, 01:05:16 pm
content: I really want to have a go at making an 12v 30amp+ smps, as im dropping the voltage I was thinking of a buck converter type.If anyone can point me to a schematic I be very greatful.I've seen a few schematic but none that can do high current.thanks

author: mariush
author_rank: Super Contributor
timestamp: August 16, 2014, 02:31:03 pm
content: It's cheaper and easier to simply get a computer power supply and remove the excess wires.You can buy good power supplies for under 50$ ... by the time you buy components and potentially custom transformer and heatsinks and make the pcb you're already at 30-50$.This will work fine:http://www.aria.co.uk/Products/Components/Power+Supplies/Non-Modular+650W+or+less/450W+XFX+Pro+Core+Edition+80PLUS+Bronze+Power+Supply+%5BP1-450S-X2B9%5D+?productId=53989

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 16, 2014, 03:08:00 pm
content: Sorry, I hold out little hope that you can accomplish this successfully or even safely.SMPS are particularly tricky kinds of circuits. In many ways, they are a house of cards where if one critical piece is disturbed, the entire circuit crashes catastrophically. And playing with direct-coupled (NON-ISOLATED) mains power is just about the MOST DANGEROUS thing you can possibly do in amateur electronics. If you have to come here and ask, then you don't have enough experience to begin doing this. Get some experience doing other things with electronics that are more safe and sane and build up your experience and confidence before trying such a very aggressive project.I don't mean to be discouraging, but you seem to want to attempt something way more than you can handle. If you want to start experimenting with SMPS, you will need to learn to wind your own specialty transformers, etc. So learning about various ferrite materials and coil-winding will be prerequisites, unless you are lucky enough to find an appropriate transformer available commercially (which would be miraculous, IME, especially for high-power). And I would recommend buying semiconductors 10 or 20 at a time, because it is very easy to blow them up without even thinking about it.Truly, I wish you luck, but I despair that you can accomplish this safely.

author: Neilm
author_rank: Super Contributor
timestamp: August 16, 2014, 04:12:12 pm
content: Quote from: snipersquad100 on August 16, 2014, 01:05:16 pmTo design any sort of SMPS (much less something like a 360W PSU) requires knowledge of the following:1) circuit design2) control theory.3) Magnetics and transformer design.4) Precise PCB layout (high current / high frequency layout isn't easy)5) EMI knowledge. Not that you need for a home project, but if you are not aware of the consiquences of poor layout, you will find the magic smoke being released every time you turn it on.6) Safety if you are looking to connect to the mains. And in many ways even if you are not connecting to the mains. I designed a control circuit for a 12V to 24V converter which had pulses of over 200V when the FET turned off.Building it requires getting a special transformer built with precise characteristics, getting the correct parts and PCBs. Don't bother trying to bread board it - the stray inductances and capacitances will wreak the system.To debug it, you will need a reasonable speed scope so you can see the various signals. I find a current probe invaluable as well for monitoring current waveforms. Note that a shunt resistor can be used but occasionally this does interfere with the performance of the system.If you want to build an SMPS, start with something powered from a bench supply to produce a say 12V 0.5A from a 20V bench supply.

author: David Hess
author_rank: Super Contributor
timestamp: August 16, 2014, 10:05:59 pm
content: As an alternative to a 12 volt 30+ ampoff-lineswitching power supply, you could use a big 50 Hz transformer for isolation and voltage step down in front of a high efficiency switching regulator. If you step down to 24 volts peak with or without a low voltage power factor correction stage (*), then a relatively simple non-isolated 50% duty cycle buck regulator will get you to 12 volts. A tapped buck inductor would allow a 48 volt input while keeping the 50% duty cycle.Before off-line switching power supplies became common, transformer isolated switching power supplies were not unheard of.If you do go the more dangerous off-line way, then consider the extra equipment you should have for design and testing like an isolation transformer and high voltage differential probes.(*) I have never seen a low voltage power factor correction stage used after a step down transformer so with apologies to Bob Pease, show me where it says it will not work.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 17, 2014, 01:57:01 am
content: Quote from: David Hess on August 16, 2014, 10:05:59 pmThat is sometimes used in UPSes. A side benefit is that the pulse charging helps the battery last longer.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 17, 2014, 08:08:29 pm
content: Thanks for the comments guys, most appreciated.I could go and just buy one but I really want to just have a go making one.I've been playing with mains since I was 10 wiring up lights, sheds and other suff, so I know how to be careful.Yes ive had a few socks over the years but hey it makes you fell ALIVE lol.Anyway I found this schematic and the parts can be purchased online. I will draw out the schematic on eagle and get the boardmanufactured.If it turns out to be a flop it wont matter cos im sure I will learn something along the way.Thanks again.

author: Mr.B
author_rank: Unknown
timestamp: August 17, 2014, 09:33:38 pm
content: I was after 12v 30A as well.I just purchased a supply from fleabay.http://www.ebay.com/itm/Compact-Lightweight-Variable-Adjustable-DC-Power-Supply-0-32V-0-32A-Output-/301258669381?pt=LH_DefaultDomain_0&hash=item46246a7d4532v, 32A.It is pretty cheap and nasty, but it does the job I want it for.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 17, 2014, 11:41:50 pm
content: Just get a PC PSU and only use the 12V rail. Even a very good one will cost less than a specialized module or homemade unit.