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[SOLVED] We need 96 separate isolated high side NFET gate drive voltages.

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opampsmoker

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Please assist…We have 96 back-to-back NFET switches which are to be switched ON/OFF occasionally. We are using 30V NFETs (3x3mm). They will carry 10 Amps when ON.
We need 96 separate High side isolated drive voltages (~12V) to switch all of these.
What is the cheapest/smallest way to get all these high side isolated drive voltages?

Transformer drive chips..
We could use 96 Max845’s with 96 Halo TGM-010P3RL transformers with voltage doubler rectifier on each output. However, I reckon the TGM-010P3RL will likely go nil-stocked…..so I am also pondering winding ninety-six 1:1:2 transformers myself on torroids.

Flyback converters:
However, I am wondering if I could do eight flyback converters, each with 13 separate isolated dsecondaries (one secondary for primary side regulation). I could make it a “triple layer sandwich wind”, with a primary of 4 series layers, with three secondaries in each “primary sandwich”.

What do you think is the “lowest component count” way of doing this?

MAX845 transformer driver

TGM-010P3RL transformer
 

mtwieg

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Photovoltaic drivers are definitely an option if you don't need fast switching speed. Also look up ASSR-V622.
 

opampsmoker

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Thanks, the Photovoltaic optos do need quite a high IF...and also, the Iout will deteriorate over time....so will the vout aswell i believe.
I just wondered, a flyback with 15vin, and 16 separate isolated secondaries of 12Vout each, but only say 1mA of output current each. I wonder what the coupling would be like for all those secondaries?
We could do multiple layer sandwiching of the primary.
Regulation would be done by a pri side regulation coil.
 

opampsmoker

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Actually i reckon a MAX845 transformer driver, with 4 isolated secondaries on a torroid is the way to go i think.

...The problem is the 12V abs max on the FET drains....the leakage L is likely to cause overvoltage spiking on these, so i would need a snubber...im surprised the datasheet does not mention a snubber.
Do you have considerations.
 

mtwieg

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Thanks, the Photovoltaic optos do need quite a high IF...
True, one trick that can mitigate this is to drive multiple LEDs in series to reduce overall current consumption, if you don't need those FETs to be controlled independently.
and also, the Iout will deteriorate over time....so will the vout aswell i believe.
Never heard of any aging issues with PV drivers.

If you want to make your own isolated supplies with a driver like the max845 or sn6501, you should look at these six-filar transformers: https://www.coilcraft.com/en-us/products/transformers/power-transformers/configurable-transformers/

Analog's isopower devices might also be worth considering. Though they also tend to be somewhat power hungry.

What's your insulation requirements?
 

opampsmoker

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Insulation requirements not really tight...i mean, say 100V.
Sorry we need all FETs to be independently ON/OFF-able

We were wondering about the attached push pull driver as a way of doing 4 isolated outputs. PDF and LTspice sim attached.
Any improvements on component count possible?

Thanks for the coilcraft recomendation..it looks liek the HPH2-1600L transformer coudl do the attached transformer job.

...however, i would suspect them of going nil-stocked and having long lead times.

I dont like the MAX845 any more, ..the 12V abs max on the internal fet drains is way too low to handle the leakage spikes.
 

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mtwieg

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Generally leakage isn't an issue so long as you use one of their recommended transformers.

There are lots of different parts for making simple unregulated isolated supplies.
MAX256 has a full bridge driver, so no worries about leakage spikes and you don't need a CT primary.
SN6505 is a push pull driver but has FETs rated for 16V and slew rate limiting, if that makes you feel better.
MAX13256 has a full bridge output and is rated to higher voltage, so you could get 12V out with 1:1 windings.

Heck, there's not much reason to even use a special purpose driver chip. Just use a cheap dual channel gate driver chip as an H bridge to drive your transformer primary. Driver all your gate driver chips with a common oscillator.
 
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