MMBT4401 Ve_b

The forward b-e voltage? I don't know how to measure, but I've exceeded it once or twice. George H.

Breakdown 7-8V

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

Thanks, Tim.

4401 is very generic, and I'd imagine different fabs might make parts with different Vbe zener voltages. So someone else's measurement might be rough.

Most parts like 4401 zener in the 5-7 volt region.

Why does it matter?

--

John Larkin         Highland Technology, Inc   trk 

The cork popped merrily, and Lord Peter rose to his feet.   
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

---------------------

** What ever makes you assume they are all exactly the same ?

Cos the number the same on each one ?

The makers of fake semis will love you.

..... Phil

I'm using it inverted. In the circuit below, I need no gain but I want the Veb breakdown to protect the gate of the FET from over voltage.

Version 4 SHEET 1 1660 1380 WIRE 176 -16 -176 -16 WIRE 544 -16 176 -16 WIRE -176 48 -176 -16 WIRE 176 64 176 -16 WIRE -176 144 -176 128 WIRE 544 192 544 -16 WIRE 544 384 544 272 WIRE 176 464 176 144 WIRE 368 464 176 464 WIRE 496 464 368 464 WIRE 176 512 176 464 WIRE 544 560 544 480 WIRE 544 560 240 560 WIRE 544 592 544 560 WIRE 176 656 176 608 WIRE 544 704 544 672 FLAG 544 704 0 FLAG -176 144 0 FLAG 176 656 0 FLAG 368 464 gate SYMBOL voltage -176 32 R0 WINDOW 3 24 44 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value 12 SYMATTR InstName V1 SYMBOL npn 240 608 R180 SYMATTR InstName Q2 SYMATTR Value 2N4401 SYMBOL res 528 576 R0 SYMATTR InstName R2 SYMATTR Value 18 SYMBOL res 160 48 R0 SYMATTR InstName R4 SYMATTR Value 121k SYMBOL nmos 496 384 R0 SYMATTR InstName M1 SYMATTR Value IRLML6344 SYMBOL res 528 176 R0 SYMATTR InstName LOAD TEXT -256 192 Left 2 !.dc v1 10 14 .01

Most any fet will stand 12 volts on the gate, and many are gate protected these days. Long-term b-e zenering can degrade transistors.

I'd add a resistor in series with the base. I've seen that sort of current limiter blow out the bipolar too many times, for no logical reason.

--

John Larkin      Highland Technology, Inc 

The best designs are necessarily accidental.

Yes, I am aware of the degradation. But will it go to a gain of less than, say, one? All I really need here is an inversion and I get free protection of the gate from supply line transients (if any). In normal operation, the base-emitter junction will not break down. The 4401 emitter and FET gate will normally be about 2 or 3 volts. If the circuit is fast enough, it will never avalanche the 4401 base-emitter junction.

That's a good suggestion. Thanks.