Linear regulators can't sink current right? If you need it to sink current you have to use an op-amp reference? I remember reading something about this a long time ago but it's so long ago I can't remember if I'm just making it up.

 

A zener diode is a shunt regulator. It can be boosted by a power transistor.

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You are undoubtedly talking about positive regulators.

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Ron

 

Hi dknguyen,

Some expensive exotic regulators can do both, even at the same time.

on1aag.

Attached Images

Exotic & expensive current source & sink.GIF (4.6 KB, 26 views)

 

If you add a load resistor on the output of a 78xxx regulator you can "sink" some current through the resistor. This is only really practical for small currents as the max "sink" current is equal to Vout/R.

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Shunt regulators can both sink and source current.

Building a linear regulator that can sink current is easy, just use a complimentary push-pull emitter follower on the output rather than the usual single transistor.

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That will work if you are building a discrete regulator, but adding it to an integrated regulator is problematic.

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Ron

 

Like polarity, sinking and sourcing are just a matter of reference. With a reference to the supply negative, a positive voltage regulator (78XX) set up as a current regulator can only "source" current to the load. But, switch to a negative regulator (79XX), with the same reference to supply negative, and the regulator is now a current "sink".

Ken

Attached Images

79XX Current Sink.jpg (10.4 KB, 8 views)

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