"rf" wrote in message
...

"Ian Jackson" wrote in message
...
In message , rf
writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.


Why not just drop the voltage through a few diodes? Very simple. Very
cheap.

A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.

More like "a *few* diodes at a couple of cents per each".

3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required. More
than good enough for the job.

Exactly one 7809 for less than a buck. No other circutry required. Perfect
regulation.



Not *quite* no extra circuitry, they require decoupling capacitors on the
input and output otherwise they can break into oscillation. If a 3-terminal
regulator feeds a circuit with a large supply decoupling electrolytic
(possibility of stored charge feeding backwards through the regulator when
the input voltage is switched off) its advisable to strap a diode between
the input and output terminals, otherwise the regulator can be damaged - not
conducting in the normal condition of input voltage being higher than the
output but conducts if the output tries to go higher than the input.