📌Summary
TVS (Transient Voltage Suppressors), also known as avalanche breakdown diodes, are devices fabricated using semiconductor processes to form a single PN junction or multiple integrated PN junctions.
📌Working Principle of TVS Diode
Unidirectional TVS diodes are typically used in DC power supply circuits, while bidirectional TVS diodes are employed in alternating voltage circuits. As shown in the figure below👇 when applied in a DC circuit, a unidirectional TVS diode is connected in reverse parallel across the circuit. Under normal operating conditions, the TVS remains in a cut-off state (high-impedance state) and does not interfere with the circuit's normal operation.
When an abnormal overvoltage occurs and reaches the TVS (avalanche) breakdown voltage, the TVS rapidly switches from a high-resistance state to a low-resistance state. This diverts the transient overcurrent caused by the abnormal overvoltage to the ground while clamping the abnormal overvoltage to a lower level, thereby protecting the subsequent circuitry from damage due to the overvoltage. Once the abnormal overvoltage subsides, the TVS reverts to its high-resistance state.
📌I-V Curve of TVS Diode
The current-voltage (IV) characteristic curve of a TVS diode is shown in Figure 2. For bidirectional TVS diodes, the curves in the first and third quadrants are symmetrical and opposite in polarity but exhibit similar characteristics, as illustrated in Figure 3.
When a TVS is reverse-biased, it operates in two modes: standby (high impedance) or clamping (relatively low impedance), corresponding to the third quadrant in Figure 2. In standby mode, the current flowing through the TVS is called the standby current (IR) or leakage current, which varies with the junction temperature of the device.
The transition from high impedance (standby) to low impedance (clamping) on the IV curve marks the onset of avalanche breakdown. Once full avalanche breakdown occurs, the TVS instantly converts the high transient voltage into a large current flowing through itself, while maintaining a relatively low clamping voltage across the PN junction.
📊Conclusion
Think of a TVS diode as a reliable bodyguard for your circuit. Most of the time it does nothing and just stands by quietly. But the moment a sudden voltage spike shows up, it jumps into action, quickly shunting the excess energy away so your sensitive parts stay safe.
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