by What is it?
Transient voltage suppressor (TVS) diodes, also known as surge protection diodes, are semiconductor devices used to protect electronic circuits from voltage transients induced by electrostatic discharge, electromagnetic interference (EMI), or inductive load switching. They function as bilateral switches, conducting current in both directions when the voltage across the diode exceeds a certain threshold known as the breakover voltage.
TVS diodes are designed to protect sensitive components like microcontrollers, memories, and custom ICs from high transient voltages that could cause damage or malfunction. Some common applications where they are used include power supplies, telecommunications circuits, automotive/industrial electronics, and data/signal lines in any digital or analog system.
Working Mechanism of TVS Diodes
TVS diodes work based on the principle of avalanche breakdown. When the reverse bias voltage across the Transient Voltage Suppressor Diode exceeds its breakover voltage, it enters a low-impedance conductive state. This shunts the excess current resulting from the transient surge safely to ground or to the opposite polarity rail, clamping the voltage level across the protected circuitry.
The clamping action occurs extremely fast, within picoseconds, safely suppressing voltage spikes and transients before they can cause any harm. TVS diodes remain in conduction mode until the transient event ends and the voltage falls below the breakover threshold again. They then revert to a high-impedance blocking state where they do not affect normal circuit operation.
Types of TVS Diodes
There are different types of TVS diodes available depending on the application, clamping voltage, surge current rating, and packaging:
Unidirectional TVS Diodes: Conduct current flowing in only one direction during transient events. Used where surge protection is needed for one polarity only.
Bidirectional TVS Diodes: Conduct current bi-directionally. Used for applications requiring suppression of positive and negative going transients.
High Voltage TVS Diodes: Have higher breakover voltages from 30V to 150V or more. Used where higher operating voltages are involved.
Low Voltage TVS Diodes: Have lower breakover voltages from 5V to 30V. Used for protecting low voltage ICs and signal lines.
High Surge Current TVS Diodes: Rated for surge currents exceeding 10kA. Used in applications exposed to very large transients.
Surface Mount Packages: Available in compact SOD, SOT, SC-70, SC-88 packages. Easier to handle and assemble for automated PCB assembly.
Key Parameters for TVS Diode Selection
When selecting a TVS diode for a given application, key parameters to consider include:
Breakover/Clamping Voltage: Should be sufficiently higher than maximum operating voltage but lower than the breakdown voltage of circuits to be protected.
Maximum Repetitive Reverse Voltage (VRRM): Upper limit of operating voltage range under normal non-transient conditions.
Maximum Surge Current Rating (Itsm): with 8/20μs pulse waveform. Determines robustness against overloads.
Capacitance (Coss): Influences switching speed and higher capacitance reduces high frequency noise suppression ability.
Leakage Current: Parasitic current during non-transient conditions. Lower is better to minimize power dissipation.
Properly selecting a TVS diode based on these parameters ensures optimum protection against transients without added performance penalties under regular operating conditions.
Importance of Earth/Grounding with TVS Diodes
Effective grounding is critical for TVS diodes to function properly in suppressing transient events. This is because the surge current must have a safe low-impedance path to flow when the TVS diode clamps the voltage.
Without a proper ground, the current may end up raising common mode voltages on data/control lines instead of being shunted away harmlessly. This can still cause upsets. It is therefore good practice to earth one side of the TVS diode closely at the PCB where it is mounted. For two-sided protection, earth both sides separately.
The earth trace width needs to be adequate based on the maximum surge current rating of the TVS. Keep earth leads as short as possible. Following good grounding practices ensures the full transient suppression capability of TVS diodes is realized without compromising EMC/EMI performance of the system.
Comparing Transient Voltage Suppressor Diode to other ESD Protection Devices
Other common standalone ESD protection devices include varistors, transzorb diodes, and gas discharge tubes (GDTs).
Varistors have higher transient current ratings but slower switching speeds compared to TVS diodes. Transzorbs combine the clamping action of a TVS with lower leakage of a zener.
GDTs provide very robust protection for AC power ports but have slow response, are not IC-compatible, require higher breakover voltages, and have limited lifetime.
TVS diodes offer the optimal balance between breakdown speed, standardized specifications, small size, cost, and wide availability in different voltage/current ratings for comprehensive transient protection at both system level and IC level. Their bidirectional protection capabilities also make them flexible for most applications.
Transient voltage suppressor diodes are extremely effective and widely used semiconductor devices for protecting electronic systems and components against high voltage transients and surges from various sources. With a proper understanding of their working principle and selection of appropriate TVS types based on electrical parameters and application requirements, robust and reliable protection can be achieved. Coupled with good grounding practices, TVS diodes constitute a versatile and affordable solution for suppressing ESD/EFT events and ensuring electronic system reliability.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it.
