Try it, then get back to us. If I were in the habit of saving blown
parts from 15 years ago, I'd be glad to mail you a few samples.
The real world doesn't run in SPICE.
You do know that the input rectifiers block substantial reverse current
flow through the regulator? When power is removed from the input, the
input capacitor will simply discharge to approximately 2x(internal
NPN)Vbc below the output at which point the output capacitor discharges
into it as well as the internal Vref and error amplifier circuitry. The
whole circuit then drifts down to zero at something like a 4-8mA rate.
You might try reading some of the earlier app notes by George Cleveland.
The idea for the reverse protection OUT/IN diode originated in a Robert
Widlar app note where he was taking care of every possible failure mode
and every possible applications abuse of the part including high
temperature, hot plug with late GND connection, and the rectifier input
filter capacitor sputtering problem. The sputtering problem was an
instantaneous input capacitor short causing high reverse current through
the regulator and permanent damage. This is categorically different from
a weak current limited discharge taking place over the order of
milliseconds. There must be literally billions of cumulative device-hour
time on existing circuits that are doing just fine without the
unnecessary reverse protection diode. As with everything else, this is
conditional. I have seen clueless application circuits where the
unregulated input is loaded by circuitry in addition to the regulator.
In this case, the reverse diode may be required, and possibly this is
what you are recalling about blowing parts.
Yay, Google Groups...
