Coupling , Load and Bypass Capacitors
10 Apr 2006 23:47:37 -0700
What are the differences between Coupling , Load and Bypass Capacitors
and what are their advantages.
Not attempting to be snide, but that's like asking what
the differencces are between tires, steering wheels
and car and what are there advantages.
Each serves a different function and each are required
for that function. Further, the categories you list are so
broad in their application that it's difficult to come up
with some comprehensive definition that makes any
Take, for example, "bypass." You have bypass capacitors
that do all sorts of tasks. For example, an emitter bypass
capacitor is in combination with the emitter resistor to
determine both the DC bias and the AC gain of a circuit.
In a feedback loop, a bypass capacitor makes the high
frequency gain of a circuit different than the low frequency
gain. And, fr all intents and purposes, the large capacitors
in the power supply can be considered bypass capacitors.
You could even have a "bypass-coupling capacitor." You
have a resistor coupling the output of one stage to the input
of another. Put a capacitor in parallel with that resistor and,
in combination with the load presented by the input stage,
you have a different coupling at some frequencies than
Indeed, you can make the argument that bypass capacitors
are coupling capaciotrs are load capacitors.
But whatever they're used for, the "advantage" is that the
circuit design requires them, simple as that.
A coupling capacitor takes the signal from one part of a circuit to
the next, while preventing and DC voltages from getting through.
A load capacitor is generally a no-no in audio. It forces a device to
deliver current, but without dissipating any power, thus resulting in
no useful work being done. Generally you want a load to be a resistor,
not a capacitor.
A bypass capacitor is something which you use in a part of the circuit
which has a vital DC function, but is not useful for the signal
itself. A power supply would be such a device. The bypass capacitor is
placed across the power supply and appears to the signal as a short
The advantage of each is generally that if you need them, and you
haven't got them, the circuit won't work. They are not some sort of
alternatives from among which you can choose the best.