For a really fine and adjustable zener look at the TI TL431C. Its
sourced by several companies these days with small variations. It
regulates at the same voltage down to under 100 microamps and is good
(depending on dissipation and package) up to 100 milliamps zener
current. It has a square knee with the corner below 100 microamps. It
can drive a power transistor for more power capability. It can be set
with a pair of resistors to regulate from 2.5 to 35 volts and with
external transistors it can work to a few KV.
Any sort of shunt regulator beats most ordinary series regulators for
minimal voltage drop, though I've designed a series regulator using
power MOSFETs for the pass transistors and the one I'm using regulates
in the negative line (good for a power supply, rotten for running off a
battery). It uses a TL431C and a 2N2907 and sufficient MOSFETs to handle
up to 30 or 40 amps with as little as .02 volts drop. There is an
analogous circuit using the LM4140 and P type MOSFETs that I've not
tried. It regulates in the positive line and should do as well.
Shunt regulators, like zener diodes, are not necessarily energy
efficient.
When I can make a regulator work down to 20 millivolts drop, the ICs
that claim "Low drop" is a volt don't quite cut it.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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