Ten Transistor Rules

Ten Rules of How Transistors Work

These are for transistors with emitter, base, and collector, not for FETs.

Learning these rules cannot come from self study. You have to talk to an engineer about them and do simple circuits. Resistors must be used, otherwise you burn out your transistor.

The rules are for NPN. For PNP, the base and collector are negative with respect to the emitter.

• 1. The three pins are emitter (with arrow), base (between the other two), and collector.

  2. A transistor is a high gain amplifier, even at 5 cents. The collector current is about 120 x base current.

  3. For base-emitter voltage less than .55V, collector current is zero. (The transistor is cut off.)

  4. For base-emitter voltage over .6V, collector current is about 120 x base current.

  5. Base and emitter are a diode. When collector and base current are flowing, Vbe is .7V.

  6. The transistor is an amplifier only when collector-emitter voltage is over .3V. Below .3V, the transistor is "saturated."

  7. Small transistors can handle about .3 watt. Big transistors can do 50 watts if they are heat sinked.

  8. A transistor can be tested with an ohmmeter.

  9. A transistor can be a digital switch, like outputs of ground and 5V, by putting emitter on ground and making it cutoff or in saturation.

  10. Don't let base get more than 6V below emitter.