Does anyone know how a Bypass Capacitor work in it's physical operation? How does a bypass capacitor filter out the ac signal in the device structure and physical operation?
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\$\begingroup\$ What has this question got to do with MOSFETs? Do you know how capacitors work? \$\endgroup\$– Andy akaApr 22, 2015 at 7:29
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\$\begingroup\$ Are you talking about a particular circuit? A diagram would be helpful in that case. \$\endgroup\$– Dmitry GrigoryevApr 22, 2015 at 7:45
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\$\begingroup\$ A simple research on google would have given you the answer. \$\endgroup\$– Dallas CarterApr 22, 2015 at 8:23
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1 Answer
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It is the same as any other capacitor. If you put DC through it, current will flow, but not for long; charge accumulates on its plates until no more can flow. At the very beginning, it acts as a short circuit. But as the charge on it increases, the voltage across it increases, to the point where no more current flows.
So when using a capacitor as a bypass capacitor, it is connected as in the diagram on the left. And when used as a coupling capacitor, it's done so as in the diagram on the right:
simulate this circuit – Schematic created using CircuitLab
To understand the circuits, I would suggest you read about RC filter circuits (Resistance-Capacitance filter circuits). The maths is simpler than other types, such as LRC or LC (Inductor-Resistance-Capacitance or Inductance-Capacitance), although you will still need some maths to appreciate how the capacitor works.
You can simulate this circuit below - it will show you how it works in practice. Click the "simulate this circuit" link below it.
To run the simulation, go through these steps:
- Click the "Simulate this circuit" link just below the diagram.
- Click on the "Simulate" button on the bottom left
- Click on the "Time domain" option
- Click "Run Time-Domain Simulation" button.
You should see a graph like this:
What you are seeing here, is the input and the output. The input is a 1V, 10Hz AC signal, with a 1V DC offsest. (So the AC signal goes from 0V to 2V peak-to-peak). After the bypass capacitor, the AC signal is largely removed, leaving just the 1V DC signal. The larger the capacitor value, the less the ripple.
