Transistors
1. Transistors Overview
The transistor is a solid-state device based on semiconductor materials, with core functions such as amplification, switching, voltage regulation, and signal modulation. Its core principle is to control the output current or voltage through a small input signal to achieve the current/power amplification effect of “controlling the large with the small”.
2. What are the Key Components of Transistors?
Transistors usually contain three electrodes:
Bipolar Transistor (BJT): emitter, base, collector.
Field effect Transistor (FET): source, gate, drain.
Among them, the base (BJT) or gate (FET) is the control electrode, and the output impedance is adjusted by the input signal.
3. What are the Types of Transistors?
Transistors are divided into two categories:
Bipolar transistor (BJT): driven by current, using two carriers, electrons and holes, and divided into NPN and PNP types.
Field Effect Transistor (FET): driven by voltage, including MOSFET, insulated gate bipolar (IGBT), etc., suitable for high frequency/high power scenarios.
4. What are the Core Features of Transistors?
Amplification Function: The small current/voltage change of the base or gate can control the large current of the collector or drain to achieve signal amplification (gain effect).
Switch Function: The on/off state is quickly switched by the control electrode signal, and the response speed can reach more than 100GHz.
Non-linear Characteristics: The output impedance changes nonlinearly with the input signal, which is suitable for complex circuit design.
5. What are Transistors Used for?
Signal Amplification: Used for small signal amplifiers (such as audio amplifiers) and power amplifiers (such as RF circuits).
Logic Switch: Constructs the logic gates (AND/OR/NOT, etc.) in digital circuits.
Power Management: Used for current control in voltage regulators and switching power supplies.
Display Technology: Thin Film Transistors (TFTs) drive pixels in liquid crystal displays (LCDs).
6. Technology Development of Transistors
Process Breakthrough: The transistor process in the laboratory has broken through the physical limit of 1nm (Berkeley Laboratory achievement in 2016).
High-frequency Application: High-frequency transistors (such as RF transistors) are widely used in 5G communications and radar systems.
7. Complementary Devices and Selection for Transistors
Complementary Pairs: Such as NPN BC546 and PNP BC556, with symmetrical parameters, are used in push-pull amplifier circuits.
Packaging Style: TO-92, SOT-23, QFN, and other packages are suitable for different power requirements.
As the cornerstone of modern electronic technology, the diverse functions and structural evolution of transistors continue to promote the miniaturization and efficiency of electronic devices.
8. Transistors FAQs
1) Is the transistor an active or passive component?
Transistors are active electronic components (Active Components), which need to rely on external energy sources (such as power supplies) to achieve signal amplification or switch control functions.
2) What is the difference between MOS tubes and GaN HEMTs?
MOS Tube: Based on the metal-oxide-semiconductor structure, it is divided into enhancement type and depletion type, and the channel conduction is controlled by gate voltage.
GaN HEMT: Based on gallium nitride material, it has no traditional body diode, and replaces the body diode function through the reverse conduction path, which is more suitable for high-frequency and high-power applications.
3) How does the transistor achieve the amplification function?
Take the NPN transistor as an example. A small change in the base current can control the large current between the collector and the emitter to achieve current amplification.
4) What is the working principle of the MOS tube?
Enhancement NMOS: It is closed when there is no gate voltage; a conductive channel is formed when a positive gate voltage is applied, and electrons flow from the source to the drain.
Depletion PMOS: It is turned on when there is no gate voltage; it is turned off when a negative gate voltage is applied.
5) Does GaN HEMT need a body diode?
GaN HEMT does not have the body diode of traditional silicon MOSFET, but its reverse conduction path can achieve similar functions and is suitable for high-efficiency switching scenarios.
6) How to choose the right transistor model?
Parameters to consider:
Voltage/Current Rating (such as VDS, IC).
Switching Speed (such as the high-frequency advantage of GaN HEMT).
Packaging and Heat Dissipation (such as TO-220, DFN, and other packaging forms).
7) What are the common causes of transistor failure?
Overvoltage/Overcurrent: Exceeding the rated parameters of the device leads to breakdown or burning.
Electrostatic Discharge Damage (ESD): The gate oxide layer is easily damaged by static electricity.
Thermal Failure: Insufficient heat dissipation leads to excessive temperature.