Series Transistor Regulator

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I'm new to these forums so just saying hi before I make my post. The following is the diagram of a series transistor regulator. Could anyone explain, what factors here would limit the maximum current that could be supplied by this transistor-regulated supply? Any explanation is greatly appreciated.

**broken link removed**

RL is just some resistive load, Vo is the output.
 

Essentially the gain of the transistor, Beta
Io = Ie+Ib do kvl of the input section
Ib = (Vin - RzIz - Vz) / Rz
depending on what wattage of zener, choose your max Iz (I=P/Vz)
so Ic = Ib * Beta

In practice you are limited with the zener power handling. Hence in practice a darling-ton pair transistor is used to increase current gain
and so you don't have to operate the zener with it handling/dissipating too much power.


Oh and welcome to this forum:grin:
 
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The regulation is given by de voltage divisor: Vtransistor + Vo = Vcs
First Vcs must be greater than Vo.
Second Vcs is a pulsating voltage that for all situations Vcs must be Vo + Vr min, this Vmin at lest must be 2.4 ans is recomended to be more.
Third the variations depends by the amount of current: for no current no variation, for great amount of current great variations of Vcs.

greetings
 
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There are also thermal considerations. The junction temperature of the transistor must not be allowed to exceed the maximum rating (Usually 150 or 175 deg C for a silicon transistor.)
 
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