The working state of the transistor, the three working states of the transistor

Forward bias: The voltage at the p-terminal is higher than that at the n-terminus.

Back-bias: The voltage at the n-terminal is higher than that at the p-terminal.

Cut-off: be 0 or inverted, bc 0 or inverted.

Amplification: be biased, bc is biased.

Saturated: be biased, bc biased.

Reversed: Be inversely biased, BC is forward-biased (there is no amplification effect when reversed).

The transistor has a pn junction, and when the p-terminal potential is higher than the n-terminus, it is positively biased, and vice versa. Details are available in Tsinghua University's "Concise Course of Analog Electronic Technology".

There are three main working states of transistors. 1. As of the state. When the transistor transmitting junction is back-biased and the collector junction is back-biased, the working state of the triode will enter the cut-off state.

This is equivalent to a closed faucet, and the water in the faucet cannot flow.

2. Amplified state. When the transistor transmitting junction is positively biased and the collector junction is reversed, it will cause the transistor to be amplified. It is equivalent to a controlled faucet, and the size of the water flowing out of the faucet is controlled.

3. Saturation state. When the transistor transmitting junction is positively biased, and the collector junction is positively biased, it will lead to a saturation state, which is equivalent to when the switch is turned on again, the outflow of water will not become larger.

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Analysis: Three working states of a transistor.

Cut-off state: When the voltage added to the transistor transmitting junction is less than the on-voltage of the pn junction, the base current is zero, the collector current and the emitter current are zero, the triode loses the current amplification effect, and the gap between the collector and the emitter is equivalent to the disconnection state of the switch, we call the triode in the cut-off state.

Amplification state: when the voltage added to the transmitting junction of the triode is greater than the conduction voltage of the pn junction and is at an appropriate value, the transmitting junction of the triode is positively biased, and the collector junction is reversed biased, at this time, the base current plays a controlling role in the collector current, so that the triode has a current amplification effect, and its current amplification factor is δic δib, and the transistor is amplified at this time.

Saturation on-state: when the voltage applied to the transistor emission junction is greater than the on-voltage of the p-n 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 does not change much near a certain value, then the triode loses the current amplification effect, the voltage between the collector and the emitter is very small, and the conduction state between the collector and the emitter is equivalent to the switch. This state of the transistor 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 judged, therefore, in the maintenance process, electronic maintenance personnel often have to take more meters to measure the voltage of each foot of the triode, so as to judge the working condition and working state of the triode.

They are the cut-off state, the saturation state, and the amplified state.

Cut-off status. When the voltage added to the transistor emission junction is less than the on-voltage of the pn junction, the base current is zero, the collector current and the emitter current are zero, the triode loses the current amplification effect at this time, and the gap between the collector and the emitter is equivalent to the disconnection state of the switch, and we call the triode in the cut-off state.

Zoom in on the state. When the voltage added to the transmitting junction of the triode is greater than the on-voltage of the PN junction and is at an appropriate value, the transmitting junction of the triode is positively biased, and the collector junction is reversed biased, and the base current plays a controlling role in the collector current, so that the triode has a current amplification effect, and its current amplification factor = δic δib, and the transistor is amplified at this time.

Saturation on. When the voltage applied to the transistor emission junction is greater than the on-voltage of the p-n 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 does not change much near a certain value, then the triode loses the current amplification effect, the voltage between the collector and the emitter is very small, and the conduction state between the collector and the emitter is equivalent to the switch. This state of the transistor is called the saturation conduction state.

The characteristic curve of the transistor is divided into four zones: saturation zone, amplification zone, cut-off zone, and breakdown zone. The first three districts are generally more discussed.

The working point of the triode enters the saturation zone, and the transistor enters the saturation state. When the transistor enters the saturation state, it is also divided into deep saturation. It can be understood like this:

When the transistor enters the saturation region and loses the linear amplification, it can be considered that the transistor is in a saturated state (q1); The transistor is in a deep saturation state (q3) when the transistor is fully driven by amplification.

There are important conditions for the saturation voltage drop of the transistor VCE(Sat), that is, VCE(SAT) under certain IB and IC conditions.

The data given in the parameter table of the transistor are also numerical values under certain conditions (the figure shows the data of the VCE(SAT) of the S8050).

It can also be seen in the diagram that when the load resistance is large (the IC is small), the value of VCE(SAT) is very small, or even less.