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Need chip to withstand surges at input to power supply

cupoftea

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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 isnt capable of handling these standards' surges. Do you know of any that do, or are we looking at a home brew circuit only?

LTC4364

MIL-STD-1275E

DEF STAN 61-005 Part 6
 

cupoftea

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The attached is the most pathetic thing you will ever see in the world of SMPS....its a Full Bridge for vin=10-36v, vout = 32v, pout = 300w.
BUT
The input has surges to DEF STAN 61-005 which means Vin sometimes goes to 175vdc for 500ms and the converter must be able to provide 32v and 300w throughout this.

So the three Surge Buck converters as shown are pretty well the only realistic way of handling the surge...but just look at the heaps of components!!!

LTspice and jpeg as attached. Also, a waveform plot of Vin, Vin at FullBridge input, and Vout during the surge, when on full load.

I think four pllel flybacks, with FETs capable of handling 350V, would be a better way?
Would you agree? (ie, instead of three surge bucks and one Full Bridge)
 

Attachments

  • 300W Full Bridge with 175vdc surge_1_230124_waveforms.jpg
    300W Full Bridge with 175vdc surge_1_230124_waveforms.jpg
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  • 300W Full Bridge with 175vdc surge_2_230124.jpg
    300W Full Bridge with 175vdc surge_2_230124.jpg
    221.4 KB · Views: 8
  • 300W FullBridge with SurgeBuck______1_3PLLEL.zip
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Last edited:

BradtheRad

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So the three Surge Buck converters as shown are pretty well the only realistic way of handling the surge...but just look at the heaps of components!!!
Though I'm not the professional engineer you are...
nevertheless I picture some budget-minded supervisor (at some step on the R&D path) who examines this and says: "75 percent of the unit laying idle most of the time? Negatory...It's wasteful even if we have to meet military spec.
The more components inside, the more there is to go wrong.
Bring me a design that accepts 10V to 175V supply. Change duty cycle instantly. Make 2 or 3 interleaved if you have to..."
 

KlausST

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Hi,

Sorry, I did not read the whole thread, thus my reply may be redundant.

If the voltage is up to 175V just for 500ms, then I'd try series transistors (Mosfets, a couple in parallel) at the input.
(As linear voltage limiter)
In overvoltage worst case thay have to dissipate (175V - 36V) x 9A = 1.2kW for half a second.
This is 600Ws or 600Joule.
Mounted on a 100g aluminum block it will just cause a temperature rise of less than 7°C.

Klaus
 

cupoftea

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If the voltage is up to 175V just for 500ms, then I'd try series transistors (Mosfets, a couple in parallel) at the input.
Thanks, though as per post #15, the SOA of FETs and BJTs just isnt up to it.
 

KlausST

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Hi,

I did a quick search at farnell. Just did P-Ch:
2 of IXTK90P20P in parallel should safely do the job.

Did not search for: BJTs, darlingtons, N-Ch, Modules....
I´m sure there are better devices than the IXTKxxx

Klaus
 

cupoftea

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I did a quick search at farnell. Just did P-Ch:
2 of IXTK90P20P in parallel should safely do the job.
Thanks, they have "hot rdson" of 88mR.
Two in pllel would be 44mR.
There is 28A flowing when vin is 12v....so thats 34W of dissipation when the surge isnt there, which is too much for us.....specially since they also cost some £20 each.

...we come up with this same sort of problem even with NFETs.
 

Easy peasy

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200V mosfets - or 600V SiC throughout ... ?
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Last edited:

cupoftea

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Thanks EasyPeasy, liked the 6.7mR SiC but at £63 its outside our budget.

The attached appears to be THE way to implement this ugliest of all converters...the Surge Buck Converter.
Needs the hi side supply to be added for the gate drives.
The delay time on the high current sensing comparator is the key to the whole thing.....making it about 150ns in delay time sounds about right.
Basically the LT1243's are set up in constant off time mode, and just make the comparator's stay tripped for approximately 2us, instead of tripping repeatedly in a high frequency oscillation.
So they are kind of just behaving like monostables.

Would you agree?
(LTspice and jpeg attached)
 

Attachments

  • Surge Buck 300W.jpg
    Surge Buck 300W.jpg
    198.8 KB · Views: 4
  • Surge Buck_300w_2NFET.zip
    5.4 KB · Views: 4
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