It should be possible with the LM2950 regulator family to regulate 12
volts internally with only a half volt head room or with a FET circuit
I've sketched to regulate with only 50 millivolts of head room. I use a
variety of the circuit on my station supply (but for convenience in
large FETs it regulates the negative line) to get a linearly regulated
supply with very good efficiency. I've measured 85% from AC input to DC
output. The unregulated voltage at no load is only 16 volts so I don't
feel a need for a crowbar either. Something I need to get more organized
and published.
Likely the slightly lower power cuts down on power circuit voltage
drops, might be helped by larger wire in the power cord, better fuse
holders, and better low voltage fuses. In such a situation one should
always use 32 volt rated fuses rather than 130 or 250 volt rated fuses
because the element of the low voltage fuse has a shorter blowing
section and thus lower resistance to cause voltage drop.
73, Jerry, K0CQ
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