Triode working principle
Nov 02, 2019| Stay Charging Safely with SChitec
Triode working principle
There are two types of crystal triodes (hereinafter referred to as triodes) according to materials: tantalum tubes and silicon tubes. Each of them has two structural forms, NPN and PNP, but the most commonly used are silicon NPN and 锗PNP triodes (where N is the negative meaning (representing Negative in English), and N-type semiconductor is in high purity silicon. The addition of phosphorus to replace some of the silicon atoms produces free electron conduction under voltage stimulation, while P is positive (Positive) is to add boron to replace silicon, which produces a large number of holes to facilitate conduction). In addition to the different polarity of the power supply, the two work the same principle.
For the NPN tube, it consists of a P-type semiconductor sandwiched between two N-type semiconductors. The PN junction formed between the emitter region and the base region is called the emitter junction, and the PN junction formed by the collector region and the base region. For collector junctions, the three leads are called emitter e (Emitter), base b (Base), and collector c (Collector).
When the potential of point b is higher than the potential of point e by a few volts, the emitter junction is in a forward bias state, and when the potential of point C is higher than a potential of point b, the collector junction is in a reverse bias state, and the collector power source Ec is higher than the base. Extreme power supply Eb.
When manufacturing a triode, it is conscious to make the majority carrier concentration of the emitter region larger than that of the base region, and the base region is made thin, and the impurity content should be strictly controlled, so that once the power is turned on, the emitter junction is positively biased. Most carriers (electrons) in the emitter region and majority carriers (holes) in the base region easily diffuse across the emitter junction to each other, but because the concentration base of the former is larger than the latter, the current through the emitter junction It is basically an electron flow, and this electron flow is called an emitter electron flow.
Since the base region is very thin, and the reverse bias of the collector junction, most of the electrons injected into the base region pass through the collector junction and enter the collector region to form the collector current Ic, leaving only a small amount (1-10%) of electrons. The holes in the base region are recombined, and the holes in the base region to be recombined are replenished by the base power source Eb, thereby forming a base current Ibo. According to the principle of current continuity:
Ie=Ib+Ic
That is to say, by adding a small Ib to the base, a larger Ic can be obtained at the collector. This is called current amplification, and Ic and Ib maintain a certain proportional relationship, namely:
11=Ic/Ib
Where: β1-- is called DC amplification,
The ratio of the amount of change in the collector current ΔIc to the amount of change in the base current ΔIb is:
β= △Ic/△Ib
In the formula, β- is called the AC current amplification factor. Since the values of β1 and β are not much different at low frequencies, sometimes for the sake of convenience, the two are not strictly distinguished, and the β value is about several tens to more than one hundred.
11=Ic/Ie (Ic and Ie are the currents in the DC path)
In the formula: α1, also known as DC amplification, is generally used in a common base configuration amplifier circuit, and describes the relationship between the emitter current and the collector current.
α =△Ic/△Ie
The α in the expression is the AC common base current amplification factor. Similarly, α and α1 are not much different when inputting small signals.
For the two magnifications describing the current relationship, the following relationship
The current amplification of the triode actually uses a small change in the base current to control the large change in collector current.
A triode is a kind of current amplifier component, but in actual use, the current amplification of the triode is often converted into a voltage amplification by a resistor.