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Thread: Shunt Regulator
face picon face BY : Olin Lathrop email (remove spam text)

> For those that like to make their own circuits instead of
> buying them pre-packaged, I offer the attached GIF of a simple
> shunt regulator circuit that I use as a zener replacement.
> If you use a power transistor and adequate heat sink, you will
> have the equivalent of a power zener.

A possible improvement to your circuits would be to use a real zener as the
voltage reference.  You are implicitly using the base-emitter voltage of the
first transistor as a voltage reference.  This will provide regulation, but
is very dependent on temperature and current.  An easy way to add the zener
is to put it in series with the emitter of the first transistor.  The B-E
junction is still in there, but will be a lower fraction of the overall
voltage reference.  The down side is that the overall clamping voltage can
not be lower than the zener plus the B-E junction voltage.  Other topologies
can use just the zener as the reference, but those are significantly
different from what you showed.

Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olinspamRemoveMEembedinc.com, http://www.embedinc.com

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