Series Pass Transistor?

[myql]

Can somebody explain to me what is a series pass transistor (bipolar or MOSFET)?

Can you give me some site regarding this matter so I can study it also.

And also if possible can you post the circuit for series pass tansistor.


Thanks

 

[LvW]

When a transistor is used primarily not as an amplifier but as an "analog gate" which controls the current flowing through it, it is called sometimes "series pass transistor" .
A classic example is a linear voltage regulator (LDO) in which a transistor controls the current which produces the output voltage.
You can find a lot of information about LDO´s also in several topics of this forum.

 

[Maddogg6]

aka 'common base' configuration.

 

[LvW]

aka 'common base' configuration.

No, for regulators only common emitter (source) or common collector (drain) is used.

 

[laktronics]

Hi,
I suppose the phrase 'series pass element' is often used in connection with series voltage regulators. For such regulators, the conductivity of the series element (transistor or MOSFET) is changed in such a way to provide a near constant voltage at the output and the difference between the instantaneous input voltage and output voltage is dropped across the series element. Whenever the output voltage tends to change due to variation in the input voltage or load current, the change in output voltage, usually referred to as 'error voltage' is amplified and applied as negative feedback to the series element so that the drop across the element changes in such away as to compensate for the initial change in voltage.

Regards,
Laktronics