Gamma-Safe Anti-Charge Protection

[katzohki]

Hi All,

I need to prevent charging of a battery (i.e. stop reverse current flow). It needs to let about 30A flow forward (peak, typical 10A or 2 standby). Diodes just aren't cutting it due to the voltage drop (this was a last second addition and we don't have much margin due to using a single battery cell). I tried some nice low Rdson power MOSFETs with a 3rd pin to activate the gate when the pack is plugged in and they worked great. Unfortunately they got destroyed by gamma radiation. We need to sterilize these with about 40kGy gamma.

If any of you have any ideas that would help me out I would truly appreciate.

Thanks!

[amyk]

Look for "rad-hard MOSFETs"... but 40kGy seems to be quite extreme. Some lead shielding, perhaps?

[Cerebus]

We need to sterilize these with about 40kGy gamma.

Ouch! Somebody's got a big lump of ⁶⁰Co.

That's a 40kJ/kg absorbed dose of ionising radiation! That's going to be a big ask for even nominally radiation hardened parts. For instance IR spec their rad-hard MOSFETS for either 100kRads or 300kRads, that's 1kGy or 3kGy in more civilised units.

Do you have the possibility of alternative sterilisation techniques such as EtO?

[DenzilPenberthy]

If you have a 'third pin' which can activate a MOSFET, could you use that pin to drive a relay instead?

[katzohki]

We need to sterilize these with about 40kGy gamma.

Ouch! Somebody's got a big lump of ⁶⁰Co.

That's a 40kJ/kg absorbed dose of ionising radiation! That's going to be a big ask for even nominally radiation hardened parts. For instance IR spec their rad-hard MOSFETS for either 100kRads or 300kRads, that's 1kGy or 3kGy in more civilised units.

Do you have the possibility of alternative sterilisation techniques such as EtO?

This is why we were thinking we may have got the dosing wrong. Normally 40kGy (max) is what we use for an entire case of units, but we did this test run just with the FETs themselves. I don't know much about dosimetry personally. I have to ask again about EtO, but I think it was out for some reason. I think E-beam would be just as bad.

Consider some GaN transistors. Their intrinsic wider bandgap means radiation is harder to alter things. Also, they are eHEMTs, not MOSFETs, there's no oxide layer to inject charge or oxide-silicon interface to poison.

Thanks blueskull, I'll take a look into these. Hopefully that is a good lead.