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Registered Member #2273
Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37
Hey guys, I've been wanting to build my own SMPS for awhile but on a reasonable budget. Basically, I want a SMPS with these specs: 0-150V DC regulated output 0-12A current limiting
I have no experience with building SMPS, I've read theory and looked at a few schematics, but that's about it. The questions I have are: Do I need a step down transformer? Can I just rectify mains and smooth it? Should I use a buck converter? If so, what IC would you recommend or should I use a microcontroller?
I have quite a few 70A SCR pucks lying around and I was wondering if i could switch the thyristors on when the AC voltage reaches a certain point.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I think a buck converter would be a good idea. I would recommend the TL494, it works great for buck/boost converters. Here is a good buck converter example: You do not need to use the 555, or even the gate driver if a GDT is used. You could use a couple of transistors to drive the GDT, or just a mosfet driver. You could also make an OCD with only a few extra passives and a CT.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
I had uzzor's design working beautifully until i abused it too much (I think the bridge rectifier fried or something because the power side pops its fuse every time i turn it on now.) All you'd have to do to bring it up to your power requirements is modify the transformer (which uzzors has a spreadsheet for,)
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Using rectified, filtered mains is a fine idea, reasonably common in high power switchmode power supplies. This technique though does have a very poor power factor and newer supplies especially with EnergyStar ratings will have passive or active power factor correction. One example of this technique can be found in Steve Ward's big capacitor charger.
It will be very challenging to get a good single power supply that works across the wide range of operating conditions that you desire. If, for example, you want to output 1V from a 170V DC bus then with a continuous mode buck you need a duty cycle of less than 1%. In turn that would mean if you want to get close to 15A you would an enormous inductor and/or a capacitor bank that supports a buttload (metric, not imperial) of ripple current. And getting a stable control loop which responds quickly to transients and has low ripple across the entire operating space would require a pretty fancy control loop.
My recommendation is to start off building a power supply with more limited specs for an application that you have right now, and then either expanding its capabilities or building new power supplies as the application arises.
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1.8kW SMPS questions
