What does the inverted working state of a transistor mean?

一沙一世

What does the inverted working state of a transistor mean? [Copy link]

 

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In the figure below, the T1 tube is in an inverted working state. What does this mean? How are the 2.1V and 1.4V in the figure calculated?

maychang

The inverted working state of the transistor means that the original collector of the transistor is used as the emitter, and the original emitter of the transistor is used as the collector. In the inverted working state, the transistor can still amplify, but the current amplification factor is very low (only several times, not more than ten times), and because the withstand voltage of the transistor emitter junction is lower than that of the collector junction, the original emitter junction is now used as the collector junction, and of course the withstand voltage is still low (the same as the original emitter junction).

maychang

The first picture is the internal schematic diagram of a bipolar gate circuit (two-input NAND gate). In the figure, both input terminals of T1 are high level and the output is low level.

But if both input terminals are low, it is difficult to say that T1 is in an inverted working state. When the input terminal is low, the be junction is forward biased and the collector junction is reverse biased, which is a normal working state.

The two input ends are one high level and one low level, and the two emitter junctions are one forward biased and one reverse biased, so it is even more difficult to say that T1 is in an inverted working state.

damiaa

You can make a transistor to measure it and see what the inverted working state looks like in practice.

tagetage

maychang posted on 2024-5-14 08:51 The inverted working state of the transistor refers to the original collector of the transistor being used as the emitter, and the original emitter of the transistor being used as the collector. In the inverted working state, the transistor...

Thanks, I learned something.

一沙一世

maychang posted on 2024-5-14 08:51 The inverted working state of the transistor refers to the original collector of the transistor being used as the emitter, and the original emitter of the transistor being used as the collector. In the inverted working state, the transistor...

Thank you. In a normal circuit, shouldn't the transistor be operated in an inverted state? Is this circuit design unreasonable?

maychang

Yishayishi published on 2024-5-14 11:28 Thank you, in a regular circuit, shouldn't the transistor be operated in an inverted state? Is this circuit design unreasonable?

I have already said that this circuit is the internal schematic diagram of a bipolar gate circuit. It is difficult to say that the tube is in an inverted state. The inverted state is what the author of the diagram said. At least tens of billions of such chips have been produced worldwide. Do you think this design is unreasonable?

maychang

Yishayishi published on 2024-5-14 11:28 Thank you, in a regular circuit, shouldn't the transistor be operated in an inverted state? Is this circuit design unreasonable?

[In a normal circuit, shouldn't the transistor be operated in an inverted state? ]

What is a "normal circuit"? Radios, amplifiers, chopper amplifiers, etc. all have examples of transistors operating in an inverted state. Those circuits can hardly be called non-normal circuits, right?

maychang

Yishayishi published on 2024-5-14 11:28 Thank you, in a regular circuit, shouldn't the transistor be operated in an inverted state? Is this circuit design unreasonable?

T1 in the first post is not an inverted transistor, but a multi-emitter transistor with a common base. To understand what a common base is, please refer to textbooks such as "Analog Circuits".

Gen_X

The main reason is the semiconductor integrated circuit manufacturing process.

This is much cheaper to manufacture than using multiple diodes as logic input circuits.

emma2015

The inverted working state of the transistor means that the original collector of the transistor is used as the emitter, and the original emitter of the transistor is used as the collector. In the inverted working state, the transistor can still amplify, but the current amplification factor is very low (only several times, not more than ten times), and because the withstand voltage of the transistor emitter junction is lower than that of the collector junction, the original emitter junction is now used as the collector junction, and of course the withstand voltage is still low (the same as the original emitter junction).