Familiar with the electronic element- Semiconductor Triode

A semiconductor triode is a common semiconductor device, composed of P/N junction, it has two types of P/N junction, NPN and PNP, in a power supply circuit, NPN is more used than PNP. The commonly used packaging types are SOT23, T0-92, T0-126, T0-220.

Basically, the semiconductor triode has three pins, within different manufacturers, they have different definitions of three pins, we can learn from the product description.

Working principle

  • All the semiconductor triode has three pins, basic, collector, emitter, no matter which manufacturer.
  • How the NPN works, first, an input voltage added between basic and emitter, basic and emitter turn on, there will be generated a small current signal. And then add a voltage between collector and emitter, collector and emitter turn on, there will be generated a big current signal, the big current signal is a multiple of the small current signal. Semiconductor triode control circuit by this current signal.
  • How the PNP works, it’s the opposite of NPN, the emitter and basic turn on first, generates a small current signal, and then emitter and collector turn on, generate a big current signal, the NPN and PNP their current is in the opposite direction.
  • Semiconductor triodes Turn-on Voltage Drop is 0.6V-0.7V.

Three states

A semiconductor triode has three states, Cutoff Area, Amplified Area, and Saturated Area.

  • Cutoff Area, this means the semiconductor is not working, when a voltage between basic and emitter less than their turn-on voltage, the semiconductor is not working.
  • Amplified Area, when basic and emitter turn on, generate a small current signal, and then collector and emitter turn on, generate a big current signal, there is a linear relationship between this small current signal and big current signal, so we called this area Amplified Area.
  • Saturated Area, when this small current signal to a certain extent, this big current signal will not grow anymore, it reaching saturation point.

Main parameter

A semiconductor triode has three main parameters, ICM, VCEO, PCM.

  • ICM. Maximum current allowable of the collector, when a semiconductor triode working reaching a saturated area, no matter the current increases, the output current remains unchanged.
  • VCEO. Reverse breakdown voltage, this is the maximum voltage between collector and emitter allowed, if the voltage greater than VCEO, semiconductor triode will be a breakdown.
  • PCM. Maximum dissipation power is allowable of the collector. When the semiconductor triode is working, the heat generated on the collector, if it working long hours over PCM, the semiconductor will be breakdown.

For example, a semiconductor triode named MMBT3904.

  • Package: SOT-23-3
  • ICM: 0.2A
  • VCEO: 40V
  • PPCM: 0.2W