Matthew Brush wrote: > Hello all, > > I was wondering if anyone can suggest a favourite switching regulator > that I could get (or preferably sample) that is easy to build a very > high current (like 10-40 amps) power supply around. Please forgive my > ignorance. > 10-40 amps @ 1-25 volts? I would build a half bridge or forward converter with a TL494 or SG3524 to do the dirty work. You would require a 'bootstrap' power supply to power the control chip as they can take a max. 40v. Switching frequency 20+ kHz, use an IR2103 MOSFET driver - has an internal 12v supply to switch the high-side MOSFET. Use minimum 250v MOSFETs for a rectified 120VAC supply. Feedback from a dedicated winding on the toroid to the control chip. [I haven't read too much about feedback schemes yet so someone else can probably fill in the blank here] Getting 1 volt from a ~170V line would be tough. You may consider a buck fed forward converter or bridge. But don't just do a buck converter. You need isolation on an off-line converter unless you don't care about getting full DC line voltage should the MOSFET fail in the ON position. A very good book on this subject is "Switching Power Supply Design" by Abraham Pressman. > I'm looking to build a new power supply for my workbench and I'm > interested in making it as small and light/portable as possible, so I > figured a switchmode supply would be best. I've seen PWM controllers > and such, but I'm looking for something much more straight-forward. I > would like to find something similar to a linear regulator (in that it > has only a few external components) but that will require a much smaller > transformer. I've never seen a ten amp transformer, but judging by a 2 > amp one I have, it will likely be MUCH too large. The transformer in a 50kHz converter would be quite small. > > I've found several schematics on the web, but they are all a little out > of my knowledge range. I also found the "Simple Switcher" but it > doesn't seem to allow for enough current. I'm looking for something to > step down the mains (115VAC) down to a variable 1-25VDC (roughly). Does > such a product exist? I've looked at the regular component > manufacturer's websites, but I found it very hard to find something that > met my criteria (mostly came away with a lot of confusion :). I would suggest getting the book I mentioned if you have at least a little knowledge of electronics. It's $50 used but you will blow up that amount of MOSFETs if you don't bother to learn anything first. Here are a lot of links: > > I've considered making one using a PIC w/ADC for feedback and PWM for > switching, but I'll probably just end up making a lot of smoke. I've > also considered modifying a PC Power Supply to get the required 24VDC > from it, but again, the smoke :) > > Sorry for being such a dolt, I guess I'm just looking for that magic > part that will let me hook up a smaller transformer, inductor, and the > few other components required for a simple SMPS. > "simple" and "SMPS" don't usually go together. Do you have a scope? It's almost necessary if working with things like this. Here's an example of a working SMPS that Bob Blick designed: It runs from 12v and puts out several voltages. Running off-line is slightly more complicated. Read datasheets on the control chips I mentioned above [ try looking at the UC3843 as well ] This is a link to the datasheets on my computer, I have all of the ones I mentioned: Check the SMPS Info directory as well: > Thanks so much in advance to anyone for their help. Hopefully that gets you moving somewhat. -- -- Martin Klingensmith http://infoarchive.net/ http://nnytech.net/ -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu