Electronics > Power/Renewable Energy/EV's

Need chip to handle surges at power supply input?

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Faringdon:
Hi,
We are doing a Full Bridge, 10-36vin, 32vout, 300wout, 125kHz.
The input will see surges to MIL-STD-1275E and also DEF STAN 61-005 Part 6.

The LTC4364 is the beefiest of all offTheShelf surge protectors, but isn't capable of handling these standards' surges. Do you know of any that do, or are we looking at a home brew circuit only?

LTC4364
https://www.analog.com/media/en/technical-documentation/data-sheets/ltc4364-1-4364-2.pdf

MIL-STD-1275E
http://everyspec.com/MIL-STD/MIL-STD-1100-1299/MIL-STD-1275E_45886/

DEF STAN 61-005 Part 6
https://global.ihs.com/doc_detail.cfm?document_name=DEF%20STAN%2061%2D5%3A%20PART%206&item_s_key=00517937

David Hess:
Long ago when I had to meet that standard, or a very similar one, I used a source follower in front of the regulator to increase the input voltage capability.  In that case I could tolerate the increased voltage drop since I was dropping the voltage anyway, but the same idea could be used with a charge pump to provide drive to the gate allowing essentially zero voltage drop.  Then if the input voltage rises, even quickly, the source follower will maintain the same output voltage.  If the voltage rises too high, over-voltage detection should cut the gate drive off shutting off the power MOSFET and preventing it from being destroyed.  Surge capability is then only limited by the voltage rating of the power MOSFET.

The control circuits for this draw very little current, making them easy to protect, perhaps with the same lower current circuit that I used.

Faringdon:
Thanks, having that follower sounds good....the surges here are up to 250V, and so it means, AYK, that the source follower has 30A flowing through it, with a drop of some 250-36V flowing through it....for the duration of the surge.......which is long, but the exact duration doesnt seem clear from the standard.
DEF STAN 61-005 part 6 we dont even have, you have to pay for it.

I am just wondering if we should add a boost converter at the front end...boost up to 100Vin...and then simply switch out the input surge  if it goes above 100V....then the Boosters output cap can serve the innput current for the duration of the transient.?

David Hess:
When I did it the requirement was that there be no damage to the device, and it had to resume normal operation after the surge.

A 300 watt boost converter is not a trivial addition, and does not inherently disconnect from the input but instead passes the surge on, requiring even more complexity.  SEPIC converters are sometimes used because they provide DC isolation from input to output, but are questionable at 300 watts.

Even if you use a switching topology that can handle high voltage surges at the input, I would still want to current limit and disconnect before the input capacitor.  But what would be wrong with sometimes like a forward converter but with the input switches rated for much higher voltage so that it can just stop switching during the surge?

Faringdon:

--- Quote ---A 300 watt boost converter is not a trivial addition, and does not inherently disconnect from the input but instead passes the surge on, requiring even more complexity
--- End quote ---
Thanks, yes, you are right, but if the surge is up to 100v, and the output of the booster is 100v normally, then who cares if the surge gets through?....its just the normal input voltage to the follow-on full bridge SMPS....we would just put a bypass diode to bypass the boost inductor when the surge happened.

But you are right, a 300W boost is not trivial, and in fact, i think it would need to be two dual_cascaded_boosters in parallel........since 10v to 100v boost at  300W/2 will need a cascaded booster.....then two in parallel due to the 34A of input current that you get when vin is just 10V.

So i think a custom linear regulator with a fast response will be required.....its going to be a real chunker of a solution though.

The thing i like about front end boosters , especially paralelled and interleave switched, is that they really reduce the diff mode input filter inductor requirement.

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