Hi all,

Can anyone tell me whether 78xx series regulators are stable with negative
resistance loads (i.e., where the current decreases as voltage increases,
even though the sign of the voltage and current is the same)? If so, what
are the constraints on the load impedance (i.e., how negative can it be?
How much capacitive load in addition to the negative resistance?).

I'm asking because I have a circuit where I was planning on using a 7824 to
feed the input of a switching power supply. I need to be able to power a
device which expects an input voltage between 20 and 32 volts from a
battery supply that can vary between 12 and 18 volts. The device is
somewhat sensitive to noise on the input (so says the manufacturer,
although it seems doubtful given that it has a switching supply internally)
so I was planning on using one of national's "simple switcher" ICs to step
up the battery voltage to 28v, and then regulate it down to a clean 24
using the 7824.

Thanks,

Sean

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