How to determine the damage of Schottky diode

How to determine the damage of Schottky diode
Schottky diodes are widely used due to their low forward voltage drop and fast switching characteristics, especially in power management and high-frequency circuits. However, due to its structural characteristics and application environment, Schottky diodes may also suffer damage.

1、 External symptoms

Similar to other types of diodes, damage to Schottky diodes often leads to a decrease or failure in circuit performance. Here are some common external symptoms:

Abnormal circuit output: Damage to Schottky diodes often leads to unstable circuit output. For example, in DC-DC converters, if the Schottky diode fails, the output voltage may experience irregular fluctuations or even complete loss of output.

Device overheating: When a Schottky diode is damaged, especially in the case of forward short circuit or reverse breakdown, the diode may generate excessive heat. This overheating phenomenon can be detected by touch or infrared temperature detector. If abnormal heating is found in the diode, it usually means that there is internal damage.

Physical damage: In some extreme cases, Schottky diodes may experience physical damage such as shell cracking, burning, or pin corrosion. These are all visual signs of severe damage to diodes.

2、 Measurement method

The most direct and effective method to accurately determine the damage of Schottky diodes is through measurement. Common measuring tools include multimeters and oscilloscopes.

Multimeter measurement method: The diode test mode of a multimeter can be used to check the forward voltage drop and reverse resistance of Schottky diodes.

Positive voltage drop measurement: Connect the red probe to the anode of the Schottky diode and the black probe to the cathode. Under normal circumstances, the forward voltage drop of Schottky diodes is relatively low, generally between 0.2V and 0.4V. If the measured voltage drop is zero or very high (close to infinity), the diode may have been damaged.

Reverse resistance measurement: Swap probes to measure reverse resistance. Under normal circumstances, the reverse resistance should be very high (close to infinity). If the measured reverse resistance is low, it may indicate that the Schottky diode has undergone reverse breakdown.

Oscilloscope measurement method: Using an oscilloscope can more intuitively observe the waveform of Schottky diodes working in a circuit. If the diode is damaged, it usually leads to abnormal rectification waveform. For example, in rectification applications, the output waveform should be a smooth DC waveform. If there are AC components or waveform distortions, it may indicate that the Schottky diode has been damaged.

3、 Common damage modes

The damage modes of Schottky diodes are closely related to their special structure and working environment, mainly including the following:

Reverse breakdown: Schottky diodes have a lower withstand voltage, typically between 20V and 60V. If the applied reverse voltage exceeds its withstand voltage value, the diode will experience reverse breakdown. This type of damage usually manifests as a significant decrease in reverse resistance, resulting in leakage or short circuits in the circuit.

Forward short circuit: When the forward PN junction of a Schottky diode is short circuited, the diode will lose its rectification function, causing the current in the circuit to directly pass through, resulting in circuit failure. During the multimeter test, the forward voltage drop of the diode with a forward short circuit is almost zero, and the reverse resistance is also very low.

Damage caused by high temperature: Due to the large reverse leakage current of Schottky diodes, they are prone to thermal runaway in high temperature environments, leading to diode damage. Excessive temperature usually accelerates the aging of diodes, manifested as an increase in forward voltage drop and reverse leakage current, ultimately leading to failure.

Thermal runaway: As the reverse leakage current of Schottky diodes increases with temperature, it may lead to thermal runaway, where the higher the temperature, the greater the leakage current, further increasing the temperature and ultimately causing diode damage. This situation often occurs in cases of poor heat dissipation or prolonged high load operation.

The damage of Schottky diodes can have a significant impact on circuit performance, so their working status must be closely monitored during design, use, and maintenance. By observing external symptoms, measuring with a multimeter and oscilloscope, and understanding common damage modes, it is possible to effectively determine whether the Schottky diode is damaged, and take necessary measures to replace or adjust it to ensure the stable operation of the circuit.