The design of power switches is crucial in modern electronic devices. Whether it is a mobile phone, computer, or large industrial equIPMent, the efficiency and stability of the power supply directly affect the performance of the entire machine. In this regard, bipolar transistors (BJTs) and metal oxide semiconductor field-effect transistors (mosfets) are two common switching elements. This article will delve into their working principles, advantages and disadvantages, as well as their applications in power switches.

1、 Introduction to Bipolar Transistor (BJT)

Bipolar transistor is a semiconductor device that uses current to control current. There are two main types of BJTs: NPN and PNP. Its working principle is to control the base current through small signals, thereby achieving control over the large current between the collector and emitter.

Working principle

In NPN BJTs, when there is sufficient forward current at the base, the current flow between the emitter and collector is amplified. This characteristic makes it very suitable for analog signal amplification and switching applications.

Advantages and disadvantages

Advantages:

Good linear amplification performance, suitable for analog signal processing.

Relatively low cost and mature manufacturing process.

Disadvantages:

The switching speed is relatively slow, usually in the microsecond range.

Low input impedance may lead to complex driver circuit design.

2、 Introduction to Metal Oxide Semiconductor Field Effect Transistor (MOSFET)

MOSFET is a voltage controlled semiconductor device, divided into enhancement type and depletion type. Its working principle is to control the conduction and shutdown between the source and drain by applying voltage to the gate.

Working principle

When a positive voltage is applied to the gate of an enhanced MOSFET, a channel is formed between the source and drain, allowing current to pass through. After the gate voltage is removed, the channel is closed and the current is cut off. This characteristic makes it widely used in switch mode power supplies.

Advantages and disadvantages

Advantages:

Fast switching speed, up to nanoseconds, suitable for high-frequency applications.

High input impedance and simple driver circuit design.

Disadvantages:

The cost is relatively high, especially in high-power and high-frequency applications.

It performs less stable than BJTs in high temperature environments.

3、 Comparison of the Application of Bipolar Transistors and MOSFETs in Power Switches

In the selection of power switches, BJTs and MOSFETs have their own advantages and are suitable for different occasions.

Application scenarios of BJT

Low frequency applications: Due to the slow switching speed of BJTs, they are suitable for low power low-frequency switching applications.

Analog circuits: BJTs are widely used in some analog signal processing due to their excellent linear characteristics.

Application scenarios of MOSFET

High frequency switching power supply: MOSFET is very suitable for use in switching power supplies (SMPS) and DC-DC converters due to its fast switching capability.

High power applications: MOSFETs have a relative advantage in high-power applications that require fast switching and low conduction losses.

4、 Summary

Choosing the appropriate switching components is crucial in power switch design. Bipolar transistors and MOSFETs have their own advantages and disadvantages, and are suitable for different application scenarios. BJTs occupy a place in low-frequency and analog circuits due to their low cost and good linear characteristics, while MOSFETs are favored in high-frequency and high-power applications due to their fast switching capability and high input impedance.

Fushite Technology focuses on the field of power devices, providing customers with power devices such as IGBT and IPM modules, as well as MCU and touch chips. It is an electronic component supplier and solution provider with core technology.