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Old 23rd April 2008, 06:40 PM   #11
luka is offline luka  Slovenia
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Hi

BTW trafos primay is driven with ~160Vdc not 120Vac
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Old 24th April 2008, 02:00 AM   #12
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Quote:
Originally posted by luka
Hi

BTW trafos primay is driven with ~160Vdc not 120Vac
True, but you get the idea

I like that the transformer was easy to mount to veroboard, and in general MUCH easier than using a toroid. IMO it looks better too.

I used such big MOSFET transistors because I'll use this as a test supply, and I expect it to get overloaded once in a while. For simplicity, I did not want to do parallels. That's why I used such overrated pieces. They seem to never get hot with a heatsink on them yet.

Those MOSFET are real brutes, I've shorted the supply, and put heavy loads on it and even got them hot with no heatsink, and they still work fine. However, I've already blown a set of 75N06s

Once I get better with SMPS, and find a few better transformers, I want to use 4 pairs of those NTY Mosfets to make a much larger 12V SMPS. I love the larger TO-264 case
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Old 24th April 2008, 02:12 AM   #13
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Any recommendations on filtering? Or am I doing ok?

I used 50V 10000uf for each output rail with a 0.2uf cap across it, so I think the output has enough.

The input is inductorless, uses a 4700uf 16V cap, a 0.1uf/250V cap, and uses 12 gauge wires for power in. It seems to run fine with only 4700uf. In use, I was planning on using a large 60,000uf cap for it, connected to where the power enters the 12gauge wires for the PCB. I don't think the input inductor is necessary, but just another part to get hot, so I left it out.

I still have empty space left on the circuit board, so I may add some extra things.
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Old 24th April 2008, 10:36 AM   #14
areza is offline areza  Bangladesh
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place input cap as close as possible to fets, 2 x 4700uf may be enough, 60,000uf would cause some nice spark at the time u connect it to the battery, 10,000uf would overload fets and blow them up if soft start not used,

i m using 2 x 1000uf/25v with fets, and 110uf/400v after rectifier, hope this info would help.
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Old 24th April 2008, 12:53 PM   #15
luka is offline luka  Slovenia
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Hi

Use of smaller caps on primay side would be better for you, say 4x2200u, or something like that, even if you use 4x4700u ones, no seed to go above 15000uF for yout setup, and for output 2x1000uF will be way better then one 10000u, this is not 50/60Hz trafo, so you don't need that much capacitance, you will need to add snubber on primary and secondary side. so that it will work as it should
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Old 25th April 2008, 01:16 AM   #16
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Quote:
Originally posted by luka
Hi

Use of smaller caps on primay side would be better for you, say 4x2200u, or something like that, even if you use 4x4700u ones, no need to go above 15000uF for your setup, and for output 2x1000uF will be way better then one 10000u, this is not 50/60Hz trafo, so you don't need that much capacitance, you will need to add snubber on primary and secondary side. so that it will work as it should
I mainly used the 2x 10000uf because they were available, and since I wanted to use it for audio, I wanted big caps for bass. The large MOSFETS have no problem starting up with them, despite the large current at start, so I'll keep them in the circuit. I do have 0.2uf caps also on output as snubbers.

I'm glad you let me know, that I can get by with a smaller capacitance say 2,200 uf or so on a future SMPS design. But I don't mind a bit of overkill for audio

Now my input 4700uf is as close as possible to where the 12
V high current enters the transformer. I was considering 10000uf, but if the 4700 is plenty, then it will stay. I still have that 60,000uf cap I can put across the power leads to feed the SMPS from, so I don't think smooth power will be any issue.

So it looks good so far.

I'm working on an amplifier also, so I can use this SMPS to power it during test, and also see how much audio output can be made from this SMPS
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Old 25th April 2008, 01:19 AM   #17
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Quote:
Originally posted by areza

i m using 2 x 1000uf/25v with fets, and 110uf/400v after rectifier, hope this info would help.
Thanks. That gives me a better idea as to what other cap values I can use.

I also used a 2200uf for the smps remote 12V input to power chip+totem poles. It's the green cap in the picture.
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Old 25th April 2008, 01:43 AM   #18
RX5 is offline RX5  Philippines
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FWIW its much better to construct your OWN transformer for this... or else you will just be guessing the output current (for the xformer used)

I can see you used also CT for the output, your input is from +/-12 windings, and your output(160V windings) a CT too??

dont know they had that made...
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Old 25th April 2008, 02:07 AM   #19
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Originally posted by RX5
I can see you used also CT for the output, your input is from +/-12 windings, and your output(160V windings) a CT too??

dont know they had that made...
In my original posts, the CT terminal was on the transformer primary, but the lead was clipped off, so I just soldered a thick wire on it to get access to it. In the original ATX PSU it didn't use the center tap.

I've noticed a few transformers are also like this, but not all, so you have to look for a possible center tap when selecting the transformer.

I imagine a non-CT one can still be used, with a voltage doubler to get the two rails.
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Old 25th April 2008, 06:43 AM   #20
luka is offline luka  Slovenia
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Hi

Quote:
I'm glad you let me know, that I can get by with a smaller capacitance say 2,200 uf or so on a future SMPS design. But I don't mind a bit of overkill for audio
Sure, but first it has to work, trust me having a lot of capacitance will be nothing good now that is now working right yet.

Quote:
I do have 0.2uf caps also on output as snubbers
So? Yes you maybe filter out some highh freq. signal that is comming from trafo (>1MHz). Base element of snubber is resistor, he does all the work, C is there only to stop lower freq. and DC, by that I mean I doesn't try to filter out main voltage, which would be impossible and from this you might see that snubber MUST be before rectifiers in other words right on primary and secondary side where windings come onto board

Quote:
I was considering 10000uf, but if the 4700 is plenty, then it will stay
Capacitors aren't there to hold voltage high, like they would need with 50/60Hz transformers, they are there to provide peak current then transformer is switching... So it/ they have to have high current ripple more then capacitance. why? your battery is your power plant in this case, caps are there to provide the peak current.... Let say that current into amplifier is 100A which is a lot of watts, but current into trafo/trafos could be 150A at one part of switching cycle, which would mean that battery would have to provide this if there wouldn't be any caps. In other words, battery is to slow to react to this...that is why you have caps

Quote:
I still have that 60,000uf cap
How much current ripple does it have? if not more then 4x smaller caps...
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