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Old 25th July 2007, 11:13 PM   #1
Jay M is offline Jay M  United States
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Default Power Supply??? 12v to 20/24v? Regulated?

Sorry if I'm posting this in the wrong place!!

Here goes!

I need to find (pre made), or design and build a compact power supply? 12v in and 20/24 v out with a max of 30-40 amps.
I don't know where to begin. I think it needs to be regulated & I don't know if it should be a SMPS or not.

Any and all questions are welcome. I don't know if I explained enough to help, so please ask away!!!!!!!

Thanks, Jay M
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Old 25th July 2007, 11:20 PM   #2
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If you are going to design it. Have look at SG3524 datasheet from TI. This is very easy chip to use.

By the way, push pull topology is the best for your design
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Old 26th July 2007, 06:50 AM   #3
Jay M is offline Jay M  United States
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I should have stated that I am new to all of this and I need thigs explained to me in the simplest way possable!!

It will be used in an automotive app. So input will varry from 11v to 14.5v! I need the output to be constant 20/24v regardless of input as long as it is in the range above. It needs to be small ( 1 &1/2 to 2 times the size of a pack of cigaretes), vibration resistant, and deal with the tempature extreams that come with an automotive enviornment (under hood)!!!

I'm still tring to figure out what the exact voltage output will need to be, that is why I have a 5 v range at the moment.

Again, I need it to be efficient and really small. Because it will end up w/other components inside a water proof enclosure (probably potted for vibration and tampering. 2 other people that I have talked to have suggested a SMPS instead of anyother type. I don't understand the differances of all the types out there.

Thanks again and keep the help comming,
Jay M
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Old 26th July 2007, 09:13 AM   #4
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Quote:
Originally posted by Jay M
It will be used in an automotive app. So input will varry from 11v to 14.5v! I need the output to be constant 20/24v regardless of input as long as it is in the range above.
Sure, you can do this, by calculating your transformer winding at lowest input voltage.

It needs to be small ( 1 &1/2 to 2 times the size of a pack of cigaretes), vibration resistant, and deal with the tempature extreams that come with an automotive enviornment (under hood)!!![/QUOTE]
I build higher power than yours just in 4*10cm, which is smaller than 2 times the size pack of cigaretes.


Again, I need it to be efficient and really small. Because it will end up w/other components inside a water proof enclosure (probably potted for vibration and tampering. 2 other people that I have talked to have suggested a SMPS instead of anyother type. I don't understand the differances of all the types out there.[/QUOTE]

SMPS is the only way to go. If you want really simple one. Try boost converter. The problem with this converter is, the peak current at the main switch and ripple current at input capacitor is really high at this power level.
By the way, do you have a protel DXP? I have a sample design in protel DXP.
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Old 26th July 2007, 06:51 PM   #5
Jay M is offline Jay M  United States
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Thanks for responding.
No I do not have "Protel DXP"!

I wouldn't mind tring to build the 1st one myself, as long as it is simple enough and I had someone I could go to for help if needed.

If the cost isn't to high, finding 1 already made to fit my application would be the way to go!!

I understand a little now about "Boost Converters", after finding this.

http://en.wikipedia.org/wiki/Boost_converter

But most of this stuff is well beyond me at this point!

Thanks, Jay M
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Old 26th July 2007, 07:01 PM   #6
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For those requirements, you'll definitely need a switching converter of some sort. Although, it will be no small task to fit a ~1kW converter into two packs of cigarettes (definitely do-able though). I would probably agree that a boost converter would be your best bet, especially as a beginner, but if you want to get a better understanding of how things work, a buck converter is probably the easiest SMPS topology to follow.
To keep size down, I suggest using a high switching frequency...that'll let you use a smaller inductor. International Rectifier makes some great IGBTs for HF (>100kHz), hi-current applications (warp speed series, I believe).
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Old 27th July 2007, 03:40 AM   #7
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determine if it needs to be regulated. push-pull is a natural choice for this application. If regulation and isolation is not required, the converter can be made fairly simple and efficient as a voltage doubler. This can be done by using the locations where the MOSFETs connect to the transformer primaries as the secondaries for the diode bridge.

with a fixed duty ratio, you can make some improvements such as a regenerative snubber, and such, making efficiency higher.

Use a MOSFET such as the IRFZ44N or such depending on your switching vs static loss situation. MOSFETS can have 25mOhm on resistance. You would probably need at least two FETS in parallel per phase (4 FETS total) in order to reduce the static losses on the FETS to a reasonable level.

The above design is a DC transformer approximation with no regulation. 12V in gives about 24V out.


regulation will tend to make the supply larger, and will make the boost converter significantly less attractive. with the push-pull, the secondary inductance can be reduced if the duty cycle range is reduced, but if regulation is required, this may not be the case, further, regulation allows for certain issues that wouldn't otherwise come up. Also, the primary is almost always connected to the seconday, which reduces the ripple current of the capacitor.
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