There is a vast amount of information available on TVS diodes, and many of the resources are in Chinese, often translated from English. At the end of the article, you'll find directories and downloadable files for further reference. This content primarily focuses on the principle, characteristics, and key parameters of TVS tubes, followed by an analysis of heat selection and a summary of PCB design considerations.
The transient voltage suppressor (TVS) is a high-performance protection device that functions similarly to a Zener diode. When subjected to reverse transient high-energy impacts across its two terminals, it rapidly switches from a high-impedance state to a low-impedance state, effectively absorbing surge power from both power and signal lines. This action clamps the voltage at a predetermined level, protecting sensitive components from overvoltage damage.
Unidirectional TVS diodes behave like Zener diodes, allowing them to absorb forward surges, typically used in DC circuits where only positive voltage spikes are expected. In contrast, bidirectional TVS diodes can handle surges in both positive and negative directions, making them suitable for both AC and DC applications.
Below is a visual comparison of unidirectional and bidirectional TVS diodes:
[Image: Introduce the principle, characteristics, and parameters of TVS tube, and analyze the heat selection]
Key features of TVS diodes include fast response time, high transient power handling capability, low leakage current, controllable clamping voltage, and compact size. However, they also have some drawbacks, such as a lower breakdown voltage and higher cost compared to other protection devices like MOVs (Metal Oxide Varistors).
When selecting a TVS diode, several important parameters must be considered:
1. **Breakdown Voltage (V(BR))**: The voltage measured across the device under a specific test current (I(BR)) when breakdown occurs.
2. **Maximum Reverse Pulse Peak Current (IPP)**: The maximum pulse current the device can handle during breakdown, under specified conditions.
3. **Maximum Reverse Working Voltage (VRWM)**: The voltage across the TVS when it's in the non-conducting state, usually set at 80–90% of the breakdown voltage. It's recommended to choose VRWM values above 16V.
4. **Maximum Clamp Voltage (VC(max))**: The highest voltage the TVS reaches during a surge. This should not exceed the safe operating voltage of the protected component.
5. **Reverse Pulse Peak Power (PPR)**: Determined by IPP and VC(max), along with the pulse waveform, duration, and temperature. A typical pulse duration is 1 ms. Shorter pulses may increase the peak power.
6. **Capacitance (CPP)**: Influenced by the silicon chip area and bias voltage. Higher capacitance can affect the response time of the TVS.
7. **Leakage Current (IR)**: The small current that flows through the TVS when the maximum reverse working voltage is applied. This can impact the quiescent current in automotive electronics.
Understanding these parameters is essential for proper TVS selection and ensuring reliable circuit protection against voltage surges. Whether designing for industrial, automotive, or consumer electronics, careful consideration of these factors will help optimize performance and longevity.
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