Dave Platt wrote:

In this particular application - pass transistors in a linear
regulator - I don't see that MOSFETs would have any particular
advantage.
. . .

Someone mentioned the 2 to 4 amps of base current you'd have to supply
for bipolar pass transistors.

Good point. The base current wouldn't be wasted (it'd flow into the
load), but the need for a fairly high-current driver would certainly
complicate the circuitry and require the use of a higher-voltage
transformer and unregulated supply, compared to a MOSFET solution.

You wouldn't need it if you used FETs. I'd
look seriously at P-channel VMOS for pass devices, myself.

Might be even more advantageous to use N-channel VMOS, and regulate on
the negative side of the load. N-channel power MOSFETs are
significantly less expensive than the closest P-channel equivalents,
and there seems to be quite a bit more choice in terms of size and
rating. If I recall properly, the charge-carrier mobility in an N
channel (electrons) is a good deal higher than in a P channel (holes),
which means that N-channel MOSFETs can have smaller channel areas than
equivalent P-channel devices, hence more dice per wafer, hence lower
prices.

--
Dave Platt AE6EO
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