What is a switching diode?

Switching diode is an electronic component that utilizes the unidirectional conductivity of semiconductor materials to achieve fast switching function in circuits. Its core function is to control the on/off of current, and it is widely used in high-frequency signal processing, pulse circuits, digital circuits, and other fields.
1、 Definition and core functions
Switching diodes operate based on the unidirectional conductivity of PN junctions. When forward biased (with the P region connected to the positive electrode and the N region connected to the negative electrode), the PN junction conducts and current can pass through; When reverse biased, the PN junction is cut off and current can hardly pass through. By quickly switching the bias state, the switching diode can achieve nanosecond switching speed, which is suitable for high-frequency signal processing.
2、 Working principle
Forward bias: When the voltage in the P region is higher than that in the N region, the PN junction narrows, carriers diffuse to form a current, and the diode conducts.
Reverse bias: When the voltage in the N region is higher than that in the P region, the PN junction widens, carriers cannot diffuse, and the diode is turned off.
Switching speed: determined by the storage effect of minority carriers, the reverse recovery time (trr) is a key parameter for measuring switching speed.
3、 Key parameters
Maximum Reverse Voltage (VRRM): The maximum reverse voltage that a diode can withstand, exceeding which may cause breakdown.
Maximum Forward Current (IFM): The maximum forward current that a diode can continuously pass through, which is related to its packaging and heat dissipation capabilities.
Reverse recovery time (trr): The time required from reverse bias to complete cutoff, which affects the switching frequency. The trr of high-speed switching diodes can be as low as a few nanoseconds.
Forward voltage drop (VF): The voltage drop during forward conduction, which affects power consumption and efficiency.
Junction capacitance (Cj): The capacitance effect of PN junction requires the selection of low junction capacitance models in high-frequency applications.
4、 Type and Characteristics
Silicon switch diode:
Features: High voltage resistance, high reliability, but slow switching speed (TRR about tens of nanoseconds).
Applications: power circuits, general switch circuits.
Schottky switch diode:
Features: Low forward voltage drop (0.2-0.4V), ultra fast switching speed (trr<1ns), but low reverse withstand voltage.
Application: High frequency detection, mixing, high-speed digital circuits.
Fast Recovery Diode (FRD):
Features: TRR ranges from tens of nanoseconds to hundreds of nanoseconds, balancing speed and voltage resistance.
Application: Switching power supply, inverter.
Ultra fast recovery diode (UFRD):
Features: TRR<50ns, suitable for high-frequency rectification.
Application: Communication equipment, high-frequency induction heating.
5、 Application Fields
Communication equipment: used for RF signal detection and mixing, such as mobile phones and base stations.
Computer: As a switching element for clock circuits and logic gates, it ensures signal synchronization.
Consumer electronics: Rectify in power adapters to improve efficiency; Control the current in LED driving.
Industrial control: used for motor drive and pulse width modulation (PWM) circuits to achieve precise control.
6、 Development Trends
High speed: With the development of 5G and the Internet of Things, there is an increasing demand for ultrafast switching diodes with trr<1ns.
Miniaturization: Adopting SOT-23, DFN and other packaging, the size is reduced to 1mm × 0.6mm, suitable for portable devices.
Integration: Integrating with power devices such as MOSFETs and IGBTs to form power modules and simplify circuit design.
Low power consumption: By optimizing materials such as SiC and GaN, the forward voltage drop and switching loss are reduced.
7、 Typical application cases
1N4148: Universal silicon switch diode, trr=4ns， Widely used in high-frequency switch circuits.
BAT54S: Double Schottky switch diode, used for high-speed data transmission line protection.
MUR160: Fast Recovery Diode, trr=35ns， Suitable for rectification of switch mode power supplies.
Switching diodes play a crucial role in electronic circuits due to their unique switching characteristics. With the continuous advancement of technology, its performance will continue to improve and its application fields will further expand.