How to Use Transistors in Electronic Circuits

A transistor uses a small voltage or current to direct the flow of a much larger current. A field-effect transistor uses an electric field to control the conductivity of a semiconducting material. A bipolar junction transistor relies on electrons and holes to control the current flow. The following steps will show how to use transistors in electronic circuits.

Difficulty: Challenging

Instructions

1. Study the basic function of a transistor. Current flows from the emitter to the collector if the voltage from the base exceeds a certain value. In a switch, the base and emitter voltage is the same, and the current is either off or on depending upon the base voltage. In an amplifier, small changes in the base voltage produce a large change in the collector voltage.

2. Perform electronic switching with transistors. A switched-mode power supply is a high-power application of this function and a logic gate is a low-power application for switching.

3. Employ bipolar junction transistors in amplifiers today. They are most useful in this application because the currents in the emitter and collector are controlled with a relatively small base current.

4. Use a field-effect transistor as the preferred choice for applications involving low noise at a narrow bandwidth where the field-effect transistor's higher input resistance is an advantage over bipolar junction transistors. Both positive and negative charges are separated by the dielectric in a field-effect transistor so the voltage required for switching is greater.

5. Implement metal-oxide semiconductor field-effect transistors for low power devices. Digital circuits use metal-oxide semiconductor field-effect transistors almost exclusively and they are common in analog circuits.

Resources

• More about using transistors