There are germanium tubes and silicon tubes. Silicon NPN and germanium PNP are more commonly used. Explain that they have the same working principle except for the different power polarity.
Transistor amplification is a good use. Input a small signal to become an amplified signal. The power supply should output an amplified signal with the same shape.
signal of. From the outside, it can be said that the input signal has been amplified. This is the principle of transistor amplification.
The common switching applications of the three-stage tube include control relays, control LEDs, control LCD backlights, control optocouplers, etc. Almost all of them are used in switching circuits.
Use a triode or need the help of a triode.
The relay is a magnetic mechanical switching element, the working current is relatively large, usually need to use a triode to drive and control. Drive circuit, use
NPN transistor, high level control. In order to ensure that the transistor is in the cut-off state when there is no control signal, the relay terminal must be connected in parallel with a freewheeling two
Otherwise, the transistor may be damaged while switching the relay.
For LED circuits that need to provide a large current to work, you can consider using a triode to drive.
Field Effect Transistor (Unipolar Transistor)
The field effect tube application is conducted by the majority of carriers. It has the advantages of high input resistance, low noise, low power consumption, large dynamic range, easy integration, no secondary breakdown, and wide safe working area.
The switching circuit of field effect tube is widely used, voltage control type, low internal resistance, and it is often used in various high current switching control circuits. Such as:
Printer power switch, external power output switch, etc. Low-current switching circuits are suitable for triodes, and high-current switching circuits are suitable for FETs.
Under a certain working voltage, the field effect tube is in the on-off state, and the change of the internal resistance changes with the size of the external voltage. In order to reduce internal resistance
, You can increase the switching voltage value.
Field effect tube characteristics:
The control input terminal current is small, and the input resistance is large.
The voltage amplification factor of the composed amplifying circuit is smaller than that of the triode
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