Most selector tools make the choice for you and leave you guessing why. This one does the opposite: enter your battery, name the standoff voltage you want, and we run the same three checks our engineers run — then show you exactly where it fails and what we would change.
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Check ① — is there enough standoff? VRWM is the voltage below which the part must not conduct. The number that matters is not your nominal pack voltage but the full-charge voltage of the whole string, plus what the charger overshoots to, plus what cell imbalance adds at end of life. We multiply the maximum bus by 1.15 as the starting point. Below VRWM the part simply sits there; above it the junction is already in breakdown and the part leaks, warms, and degrades quietly.
Check ② — does the clamp stay under your MOSFET? This is the check most people skip. The datasheet Vc is measured at one specific current — for us, IPP at 10/1000 μs. A bigger or faster surge pushes the clamp higher, along the dynamic resistance. So we compare your MOSFET rating, derated to 85%, against the lowest clamping part available at that standoff. If even the best part fails, no amount of derating talk saves it.
Check ③ — is there enough surge energy? Same standoff exists in SMA 400 W through SMC 8000 W. A pack bus usually starts at 3000 W. Under-sized packages do not fail on the first hit — they fail on the twentieth.
Why we do not simply pick for you. There is a real trade-off between ① and ②: a higher standoff protects against leakage but raises the clamp and forces a bigger MOSFET. Which side to lean on depends on your charger, your cell supplier and your BOM target — things we cannot see from here. So we show you the numbers for the stand you chose, side by side with ours, and let you decide with the trade-off in front of you.
At the same standoff, a foldback device clamps far lower — at 60 V, 77.4 V instead of 96.8 V. That 19 V is often exactly what decides whether your 100 V MOSFET survives. The cost: after breakdown the device snaps back into a negative-resistance region and holds at a sustaining voltage VH. On a live bus you must confirm VH is above the maximum bus voltage, or it can latch in the low-impedance state and stay there. VH is usually not on the datasheet — ask us for it, it is the first parameter to settle.
In the tables below, parts marked foldback are the -N suffix versions.
Someone else uses a lower standoff on the same pack and it works. Why do you say no?
Because “works” and “works for ten years” are different claims. A standoff with 3% headroom survives a matched, temperature-controlled pack with a precision charger. Add one weak cell and a cold morning and the junction conducts at end of charge. If your bus really is that stable, drop the margin factor to 1.10 in Advanced and the tool will agree with you — we would rather show you the assumption than hide it.
I typed a standoff that is not in your catalogue.
Then we tell you so, and show the nearest stocked stands on both sides. We do not extrapolate a part that does not exist.
Can I order straight from this page?
The review is a starting point: it settles the standoff, the power class and the clamp ceiling. Batch, marking, packaging and automotive grade (-H suffix, built to order) still need a catalogue check line by line. Send us the summary and we will confirm in one working day.
Does this send my data anywhere?
No. Everything runs in your browser. Nothing is uploaded, stored or logged.