O'Reilly logo

Designing Embedded Hardware by John Catsoulis

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Capacitors

While a resistor is a component that resists the flow of charge through it, a capacitor stores charge. Capacitance is measured in Farads (or more formally, Faradays) with an equation symbol C and a unit symbol F. Typical capacitors you will use will range in value from μF (microFarads) down to pF (picoFarads).

The relationship between current, capacitance, and voltage is given by:

I = C * dV/dt

where dV/dt is the rate of voltage change over time.

The schematic symbols for capacitors are shown in Figure 2-10. The component on the left is bipolar, while the other two are unipolar. A unipolar capacitor has a positive lead and a negative lead, and it must be inserted into a circuit with the correct orientation. Failing to do so will cause it to explode. (Unipolar capacitors have markings to indicate their orientation.) A bipolar capacitor has no polarity.

Capacitor symbols

Figure 2-10. Capacitor symbols

Applying a voltage across a capacitor causes the capacitor to become charged. If the voltage source is removed and a path for current flow exists elsewhere in the circuit, the capacitor will discharge and thereby provide a (temporary) voltage and current source (Figure 2-11).

Capacitor charging and discharging

Figure 2-11. Capacitor charging and discharging

This is an extremely useful characteristic. A given voltage source may have a ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required