Anyone in knowing of transistor with higher than average Veb that's 5 v for most power transistors? And found Veb to be a decisive factor in at least one scheme? Using 1300x series with Veb 9v but they are for different purposes primarily and not good sonic response. Thanks in advance for your understanding 🙂
There is a forward (unlocking) voltage and a reverse (locking) voltage (BJT). The opposite is true in circuits with transformers at the input. For alloyed germanium transistors, the reverse Vbe was + 20V 🙂
Circuit engineering can be solved with the help of diodes, Zener ...
Circuit engineering can be solved with the help of diodes, Zener ...
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If you hook the ohmmeter across the BE junction on a non-Darlington transistor so that the junction is reversed biased, it will Zener over at around 5.something or so Vdc, maybe up to 6.2Vdc or so, too.
The specified Veb for most planar transistors is always very low, 5~6V, but the actual breakdown voltage for power transistors is often higher, 10V or more.
This is a technological consequence of the beta optimization, and is quasi-universal, except for chopper/muting transistors which have ~symetrical ratings, but they don't exist in power version (I think).
Older, alloyed transistors had more symetrical characteristics, but they are either germanium or prehistoric silicon, both completely obsolete
The low reverse breakdown of the emitter base junction is due to the heavy doping levels in the emitter necessary for good high gain transistor performance, and especially for low on-resistance in switching mode. Most transistors have emitter : base : collector doping ratios around 10000 : 100 : 1, which basically means the EB junction is close to being a zener junction, and the vast majority of injected carriers diffuse across the base-collector junction whether its forward biased (saturation) or reverse biased (active region) - that's how you get gain.
Its common to add protection in a circuit where the EB junction may become reverse biased and breakdown, as this is a very easy way to fry a transistor.
Even modest breakdown that doesn't damage the device will adversely affect the noise performance of a BJT. You'll see internal protection diodes back-to-back between inputs of opamps designed for low-noise, specifically to prevent this.
Its common to add protection in a circuit where the EB junction may become reverse biased and breakdown, as this is a very easy way to fry a transistor.
Even modest breakdown that doesn't damage the device will adversely affect the noise performance of a BJT. You'll see internal protection diodes back-to-back between inputs of opamps designed for low-noise, specifically to prevent this.