For power supply designers, three main types of transients must be considered when designing a switching power supply to ensure its stability and longevity. These include:
1. **Inductive transient voltage** caused by sudden changes in the load.
2. **Transient voltage introduced through the power line**, such as from lightning strikes or electrical surges.
3. **Internal transient voltage** generated within the power supply itself during switching operations.
To protect the power supply from these threats, several critical components require protection:
1. **High-voltage switching transistor (VMOS)** – which can be damaged by voltage spikes.
2. **High-voltage rectifier diode** – responsible for converting AC to DC and vulnerable to overvoltage.
3. **Output rectifier diode** – handles high current and is also susceptible to transient voltages.
4. **Internal control circuitry**, such as the pulse width modulator (PWM), which can malfunction due to voltage fluctuations.
A typical example of TVS (Transient Voltage Suppression) application in a switching power supply is shown in the diagram. There are eight TVS diodes used, each designed to protect specific components. The characteristics of these TVS devices vary significantly, including their **breakdown voltage**, **maximum pulse peak power**, **peak current rating**, and **clamping voltage**.
In a switching power supply used by a well-known company like HP in the U.S., you can clearly see the number and condition of all the TVS diodes installed. This highlights how essential they are in ensuring the reliability and safety of the power supply system.
TVS technology is widely adopted in many countries, especially in high-performance and industrial applications. The large number of TVS diodes used in modern power supplies reflects their importance in protecting sensitive electronics from voltage transients. As a result, incorporating TVS into the design is not just a good practice—it's a critical step in improving the overall reliability and lifespan of the entire system.
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