Working principle of switching triode
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Working principle of switching triode
Cut-off state
When the voltage applied to the emitter of the triode is less than the on voltage of the PN junction, the base current is zero, the collector current and emitter current are both zero, the triode loses the current amplification effect at this time, and the gap between the collector and emitter is equivalent to the off state of the switch, that is, the cut-off state of the triode. The characteristics of switching triode in cut-off state are emission junction and collector junction in reverse bias.
Conduction state
When the voltage applied to the emitter of the triode is greater than the conduction voltage of the PN junction, and when the current of the base increases to a certain extent, the collector current no longer increases with the increase of the base current, but no longer changes near a certain value. At this time, the triode loses the current amplification effect, the voltage between the collector and the emitter is very small, and the collector and the emitter are equivalent The on state of the switch is the on state of the triode. The characteristics of switch triode in saturated conduction state are emission junction and collector junction are all in positive bias. The characteristics of the triode in the amplification state are that the emitter is in the forward bias and the collector is in the reverse bias. This is also the principle that the voltage value of transmitting junction and collecting junction can be tested by Voltmeter to determine the working condition of triode. Switching triode is based on the switching characteristics of triode.
Working mode
There are many kinds of triodes, and different models have different uses. Most of the triodes are plastic or metal packages. The appearance of common triodes is that the electrode with an arrow is the emitter, the one with the arrow facing out is the NPN type triode, and the one with the arrow facing in is the PNP type triode. In fact, the direction indicated by the arrow is the direction of the current.