Schottky diodes, with their unique metal semiconductor junction structure (rather than the standard P-N junction), play several key and irreplaceable roles in electronic circuits. Its core function stems from its inherent physical properties, mainly including the following points:
Efficient rectification (especially suitable for low voltage, high frequency, and high current scenarios):
Principle: The barrier height formed by the metal semiconductor junction of Schottky diodes is relatively low.
Function: This makes its forward conduction voltage drop very low (usually between 0.15V and 0.45V, much lower than the 0.6V-0.7V of ordinary silicon P-N junction diodes).
Advantages: In rectification applications, especially in low voltage and high current situations (such as output rectification of switching power supplies, computer motherboard power supply, DC-DC converters), lower forward voltage drop means significantly reduced conduction power consumption and less heat generation. This not only improves the conversion efficiency of the power supply (reducing energy waste), but also reduces the requirements for heat dissipation, making the design more compact.
Typical applications: secondary rectification of switch mode power supplies (SMPS), power management of battery powered equipment, and freewheeling paths for motor drives.
High speed switch:
Principle: Schottky diodes are majority carrier devices. Current is mainly formed by electrons (in N-type semiconductors) or holes (less commonly in P-type semiconductors) as a carrier flowing from the semiconductor to the metal (or vice versa). It does not have the minority carrier storage effect present in P-N junction diodes.
Function: Therefore, its reverse recovery time is extremely short (usually on the order of picoseconds to nanoseconds).
Advantage: This feature makes it an ideal choice for high-frequency switching circuits. During the fast switching process (such as the switching action of switch power supplies, digital logic circuits, RF circuits), it can quickly switch from the conducting state to the cutoff state, and vice versa. This greatly reduces the energy loss at the moment of switching (switching loss), avoiding voltage spikes and oscillations caused by recovery delays.
Typical applications: clamp diodes in high-speed logic gates, freewheeling diodes in switching power supplies (connected in parallel with switching transistors), RF detection and mixing, high-speed data line protection, etc.
Continuation and protection:
Principle: Utilize its low conduction voltage drop and fast recovery characteristics.
Function: In the switching circuit of inductive loads (such as relay coils, motor windings, inductors), when the control switch (such as transistor, MOSFET) suddenly turns off, the inductor will generate a high voltage back electromotive force (opposite polarity to the original power supply voltage). Schottky diodes can be connected in parallel at both ends of the load or switch (in reverse parallel direction).
Advantage: When a back electromotive force is generated, the Schottky diode quickly conducts forward, providing a low resistance discharge circuit (freewheeling path) for the inductor current. This effectively clamps voltage spikes and protects switch tubes or other sensitive components from being damaged by high voltage breakdown. Its low conduction voltage drop means lower power consumption during the freewheeling process.
Typical applications: Relay drive circuits, motor control circuits, and protection of power switching transistors (MOSFETs/IGBTs) in switching power supplies.
Voltage clamp:
Principle: Utilizing the characteristic that the voltage remains relatively constant after the forward conduction of the diode (Schottky has a lower conduction voltage drop).
Function: Connect the Schottky diode in the forward direction between the circuit node that needs protection and the reference point (such as ground or power rail).
Advantage: When the voltage of the node attempts to exceed (when the anode of the diode is connected to the node and the cathode is grounded) or fall below (when the cathode is connected to the node and the anode is connected to the positive power supply) a certain set value (approximately equal to the conduction voltage drop of the diode), the diode will conduct, limiting the voltage within a safe range and preventing overvoltage damage to the subsequent circuit. Its low conduction voltage drop may be more suitable in certain precision clamping applications.
Typical application: Protect the input/output pins of integrated circuits from damage caused by electrostatic discharge (ESD) or transient overvoltage (often used in conjunction with other protective devices).
Prevent reverse current/reverse connection protection (some scenarios):
Principle: Utilize the unidirectional conductivity of diodes.
Function: Connect Schottky diodes in series in the positive path of the power input.
Advantage: When the power polarity is correctly connected, the diode conducts in the forward direction (due to its low conduction voltage drop, the loss is relatively small). If the power supply is accidentally reversed, the diode will reverse and cut off, preventing current from flowing back and protecting the components on the circuit board from being damaged by reverse voltage. Although ordinary diodes can also achieve it, the low voltage drop of Schottky can reduce power consumption and voltage drop losses in this application.
Typical applications: Power input protection for portable devices and battery powered equipment.
Summarize key advantages and limitations:
Core advantages: extremely low forward conduction voltage drop (Vf) and extremely fast switching speed/very short reverse recovery time (trr).
Main limitations:
Higher reverse leakage current (IR): Compared to P-N junction diodes, Schottky diodes have a larger leakage current during reverse bias and significantly increase with temperature. This is not suitable for precision circuits that require extremely high leakage current.
Relatively low reverse breakdown voltage (BV): The reverse withstand voltage of Schottky diodes is usually difficult to achieve very high (generally below 200V, often below 100V), which limits their application in high-voltage situations.
Cost: Usually slightly more expensive than ordinary silicon rectifier diodes.
The core value of Schottky diodes lies in their low voltage drop and ultra-high speed characteristics. Its strongest application areas are those that require high efficiency (low voltage drop) and high frequency (fast switching), especially in low voltage, high current rectification (such as switch power output stages) and circuits that require fast freewheeling/protection. It is an indispensable key component in modern high-efficiency power conversion, high-speed digital circuits, and RF applications. When choosing to use it, it is necessary to balance its advantages of low voltage drop and high speed with its limitations of large reverse leakage current and low withstand voltage.