Transistor as a zener diode

[Garnet]

Can anyone explain about or point me to any articles about using transistors as zener diodes ?
Why not just use zeners, and what connections (c-b short or e-b short) and their pros and cons ?

 

[yungman]

When I was doing bipolar IC design, we reverse bias the EB junction as zener diode of 6.3V. We connect the B and C together to form the cathode and the emiter as anode. I don't know what voltage you can get with any transistor, but yes, it can be a zener diode. Whether it is optimized to work as a zener or not is a different story.

That time the zener we get by reverse the EB diode has a +2.4mV/deg C, we always have to put a forward biased diode( CB as cathode and E as anode also) in series which have -2mV/deg C to cancel the drift...approximately only, still not very good.

If you do a discrete design, I would not use transistor as zener. Don't know even the long term stability and the current limit. Get a real zener.

 

[oswaler]

There are some instances where a transistor can be used as a zener diode, but this is not its intended purpose. A zener diode is specifically designed to operate in the reverse breakdown region, while a transistor is designed for amplification and switching. While a transistor may exhibit zener-like characteristics, it is not optimized for this function and may not provide the same level of precision and reliability as a dedicated zener diode.

In terms of connections, the collector-base (c-b) shorted configuration can be used to mimic a zener diode, but it may not provide the same level of voltage regulation as a true zener diode. The emitter-base (e-b) shorted configuration can also be used, but it may have higher power dissipation and may not be suitable for high voltage applications.

In general, it is recommended to use a dedicated zener diode for voltage regulation purposes as it is specifically designed for this function and can provide more precise and reliable performance. However, if you are interested in exploring the use of a transistor as a zener diode, there are some articles and resources available online that discuss this topic further. It is important to carefully consider the limitations and potential drawbacks before implementing this approach in any practical application.