Grassy said:
Thanks!, thats explained a lot, leaves/creates a few questions
Excellent! If I somehow explained everything in one paragraph, there
would be no reason to go on living. ;-)
so how do you calculate capacitor size, is it possible to put too
large a capacitor as the decoupler.
The formula that relates current to the rate of change of capacitor
voltage is a lot like the one that relates inductor voltage to the
rate of change of current through it. I=C*(dv/dt)
I is in amperes, C in farads, and dv/dt in volts per second. This
tells you that you can pass an ampere through a 1 farad capacitor and
the voltage will change 1 volt per second. The trick is to apply this
to short and variable spikes of current and calculate how the voltage
will change. Lots of people skip the calculus and find out the needed
capacitance by experiment (look at the supply voltage with a scope and
keep increasing the capacitance till the bounce gets small enough).
What size of capacitor do you need before you can feel a discharge?.
That is more dependent on the voltage stored across the capacitor,
than the size. As long as the voltage is less than about 50 volts,
dry skin will limit the current to less than a painful amount. Tough
your tongue across one, and the voltage has to be a lot lower to make
the experience not "shocking". The size of the capacitor just varies
how long the shock will go on, before the voltage has run down too low
to feel.
Building a Hulda Clarke "zapper" and that says .0047uF for decouple, If
you use a larger one, is that entire charge delivered for each pulse
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.
I guess I need to read more about capacitor charge times and discharge
rates.
They are very versatile components with lots of applications.