The role and working state of the triode

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The role and working state of the triode

Product function

The transistor has a current amplification effect, which is essentially a triode that can control a large amount of change in the collector current with a small amount of change in the base current. This is the most basic and important feature of a triode. We refer to the ratio of ΔIc/ΔIb as the current amplification factor of the transistor, denoted by the symbol “β”. The current amplification factor is a fixed value for a triode, but the base current changes as the triode operates.

Working status

Cutoff status

When the voltage applied to the triode emitter junction is less than the turn-on voltage of the PN junction, the base current is zero, the collector current and the emitter current are both zero, and the triode loses current amplification at this time, and the collector and emitter are equivalent. In the off state of the switch, we call the transistor in the off state.

Magnified state

When the voltage applied to the triode emitter junction is greater than the turn-on voltage of the PN junction and is at an appropriate value, the emitter junction of the triode is forward biased, and the collector junction is reverse biased. At this time, the base current is opposite to the collector. The current acts as a control to cause the triode to have a current amplification effect with a current amplification factor β = ΔIc / ΔIb, at which point the transistor is in an amplified state.

Saturated conduction

When the voltage applied to the junction of the triode is greater than the conduction voltage of the PN junction, and when the base current increases to a certain extent, the collector current no longer increases with the increase of the base current, but is at a certain The value does not change much near the value. At this time, the triode loses current amplification, the voltage between the collector and the emitter is small, and the collector and the emitter are equivalent to the conduction state of the switch. This state of the triode is called the saturation conduction state.

According to the potential of each electrode when the triode is working, the working state of the triode can be discriminated. Therefore, in the maintenance process, the electronic maintenance personnel often need to use a multimeter to measure the voltage of each leg of the triode, thereby judging the working condition and working state of the triode.