三极管的两个PN节

2、 Three working states of triode

Cut off state: the voltage of the emitter junction of the triode is less than the conduction voltage of the PN junction, the base current is zero, and the collector current and emitter current are both zero. At this time, the triode loses its current amplification effect. The gap between the collector and emitter is equivalent to the off state of the switch. We call the triode in the cut off state.

Amplification state: when the voltage applied to the emitter junction of the triode is greater than the conduction voltage of the PN junction, the emitter junction of the triode is biased in the forward direction and the collector junction is biased in the reverse direction. At this time, the base current controls the collector current, making the triode have the current amplification effect.

Saturated conduction state: When the voltage applied to the emitter 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 does not change much near a certain value. At this time, the triode loses its current amplification effect, the voltage between the collector and emitter is very small, and the collector and emitter are equivalent to the conduction state of the switch. This state of triode is called saturated conduction state.

3、 Function of triode

·Amplify weak signals: a small signal input from the base will cause a large current change at the collector, which is the most important and core part of the electronic circuit.

·As a contactless switch: use the cut-off and conduction characteristics of the triode to control or drive the load; For example, the gate circuit composed of triode, switching power supply, etc.

4、 Type of triode

There are many kinds of triodes, which can be classified according to different categories:

① According to semiconductor materials, there are silicon tubes and germanium tubes;

② According to the working frequency, there are low frequency tubes and high frequency tubes;

③ According to the power, there are small power tubes, medium power tubes and high power tubes;

④ According to the function, it can be divided into switch tube, power tube, Darlington tube, photosensitive tube, etc.

The common NPN type main E-tubes are: 8050, 9013, 9014, 9018, C1815, D882, TIP41, 3DD15, 2N3055, 2N3773, etc;

Common PNP triodes include 8550, 9012, 9015, B772, TIP42, 2N5884, etc.

Among them, TO-92 packaged E-tubes such as 8050, 8550, 9013 and 9012 belong to low power transistors:

D882, B772, TIP41, TIP42, etc. belong to medium power triodes:

3DD15, 2N3055, 2N3773, 2N5884 and other gold capped triodes belong to high-power triodes:

All of the above are in-line transistors, and the SOT-23 packaged patch transistors are also common:

5、 Important parameters of triode

1、 β Value:

β Value is the most important parameter of the triode, because it describes the amplification capacity of the triode to the current signal. β The higher the value is, the stronger the ability to amplify small signals is, and vice versa; However, the value cannot be very large, because it is too large, and the performance of the triode is not very stable. Generally, the value should be 30 to 80. Generally speaking, the value of the triode is not a specific value, and it generally changes slightly with the working state of the element.

2. Inter pole reverse current:

The smaller the reverse current between electrodes, the higher the stability of the triode.

3. Reverse breakdown characteristics of triode

The triode is composed of two PN junctions. If the reverse voltage exceeds the rated value, it will be broken down like a diode, causing performance degradation or permanent damage.

4. Operating frequency:

The values of triodes only remain unchanged within a certain operating frequency range. If they exceed the frequency range, they will drop sharply with the increase of frequency.