Seem like everyone forgets that zener diodes actually subtract their
voltage if placed in series.  e.g. I would use a 1N4730A in series with
the 9V.  That would give you 9V - 3.9V = 5.1V ... perfect supply up to
1W!  Although it does not regulate, you really don't need regulation in
your example as I see it.  I would also use a 1N400x series diode for
reverse polarity protection - if so just use a 1N4728A to make up the
additional voltage drop.

MGB,

- Mike



>
>
> William Chops Westfield wrote:
>
>> On Jun 29, 2004, at 9:29 PM, Chetan Bhargava wrote:
>>
>>> Yes, I agree on that but eight year old kids don't want to know the
>>> working of the circuit, they just want to finish the kit and see the
>>> LEDs blinking :-)
>>
>>
>>
>> Oh, I agree on not knowing the workings, but having neat looking parts
>> instead of just black blobs is an advantage, too.  Maybe LEDs and a
>> chip and some current limitting resistors are enough.  After all, you
>> can't get much cooler than LEDs...
>>
>> BillW
>>
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