Electrical Components


A diode is a component that allows current to flow in one direction only. The symbol used for a diode is usually like this with a solid triangle: -->|--.

Diodes have two parts: an anode and a cathode. The anode is what precedes the (directional) diode (the triangle in schematics) and the cathode is what succeeds it (the bar in schematics).

When a forward bias is applied (positive on the anode, negative on the cathode), the current will flow. There is a forward voltage drop that occurs, and it varies by diode.

Rectifiers are diodes designed to handle large currents, used often in power supplies to convert AC into varying DC.


A transistor is a component that controls the amount of current that flows through one terminal by current or voltage applied to another terminal. Transistors exhibit gain, so are often used as amplifiers.


A common transistor is a bipolar junction transistor. It has three terminals: a base, a collector, and an emitter. The base acts as the input, and when voltage is applied to it, a small amount of current flows through the base-emitter junction (this is usually preceded by a resistor, to protect the transistor from burning out). This allows the emitter-collector current to flow. A transistor, in this case, is effectively a single-pole single-throw switch, allowing current to flow only when voltage is applied at the base.


A field-effect transistor operates similarly to the BJT, but has differently named terminals and a slightly different way of operating. The terminals used are gate, drain, and source. Instead of current across the base to allow the emitter-collector current to flow, it uses voltage across the gate to allow the source-drain current to flow.


A relay is an electrically operated switch. Early relays were operated by an electromagnet, but are now solid-state with semiconductors.


  1. https://yewtu.be/watch?v=YtM_MnM0qT4

Last modified: 202212070107