How Does a Rectifier Diode Work?

By G.K. Bayne

Common Uses

Rectifier diodes, although hidden from sight, are a part of our everyday lives. These small semiconductors regulate the power in computers and the electrical power in our cars and trucks. Without the efficient rectifier diode, battery chargers for rechargeable batteries, computer power supplies and vehicle batteries would not exist.

AC Power

The power for homes and cars is alternating current (AC). This means that for every second, the AC goes from zero to maximum voltage 60 times a second (60 Hertz). In fact, if you look at the diagram below, you will see that the power actually goes from a negative value to a positive value. This one cycle is called a "full sine wave."

One Way Diodes

A rectifier diode acts as a restrictor to one half of the AC. This small semiconductor can be placed in an electrical circuit to either restrict the negative part or the positive part of the alternating current. In the diagram below, the left half wave is all negative, while the right portion of the diagram shows an all positive half wave. This type of power regulation is used for your computer's power supply where the circuitry needs both positive and negative voltage to operate. (This type of power is called direct current.) The diode allows only one waveform, either positive or negative to pass by its circuit.

Car Alternators

Automobile batteries must remain charged to start the engines as well as to provide efficient power for the modern computers in today's cars and trucks. An alternator does just that, but it needs the rectifier diode to finish the job. All vehicle power is produced in a three-phase waveform. As the diagram below shows, these waveforms are 120 degrees apart. With the use of the rectifier diode and the negative waveform removed, the positive waves are almost at a complete peak of direct current (DC). This positive 12-volt DC power keeps your battery charged and runs all the electrical equipment in your vehicle.