Re: decoupling capacitors

On Mon, 27 Feb 2006 12:29:48 -0500, John Popelish wrote:

Grassy Knollington wrote:
On Mon, 27 Feb 2006 01:15:49 -0500, John Popelish wrote:

Decoupling caps do not normally discharge during circuit operation.
They just sit there across the supply lines, holding a nearly constant
voltage. I would have to see a schematic to be sure what they are
describing is really a decoupling cap, and not some other circuit
function.

http://www.zapperlab.com/ZapSchematic.gif
(snip)

The only capacitor performing a decoupling function in this schematic
is C1. And it is not bypassing the battery lines, but 2/3rds of that
voltage divided down by an internal resistor divider in the 555. The
CV label on the pin refers to the use of this fraction of the supply
as a control voltage (that is compared to the voltage on pin 6, to
decide when to reset the output flip flop). See:
http://www.uoguelph.ca/~antoon/gadgets/555/555.html
Here, the decoupling action is greatly improved by the resistors
between the CV pin and the supply rails.

Thats a useful reference ta, do you mean the test circuit on this
page where 2 resistors and 2 leds cross and join the output pulse line

On the zapschematic.gif, if I put a 4.7 uf capacitor (or what size
would you recommend) across the power terminals would that help the
circuit at all?

WOW, wish I had continued to study electronics 20 years ago when I
started... got into software design/prog instead... Never too late I guess!
.

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