Shouldn't happen. An often overlooked design error is to put large
capacitors on the output of a 78xx regulator. Should the input drop
below the output (large filter on output, filter and heavy load on input
senario), the regulator will blow. A circuit as you described with a
chain of two or more regulators, with each supplying a load, will
develop this problem. Some datasheets suggest a 1N4001 across each
reguloator in/out with the cathode to the input. This insures the input
will never drop more than .7 volts below the output as the circuit
discharges.
Rick

Hi!

I have very simple power supply, consisting from transformer 220/12V,
bridge, 2200micro cap, 7812 regulator, another 2200micro cap to get 12V.

From 12V I have 7805 regulator and yet another 2200 micro cap. The
problem
is, that 5V rises too slow to reliably start my 16f877. Is there any
simple
way ( except smaller caps) to make 5V rise faster?

Regards, Samo

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