What Is a Transient Voltage Surge Suppressor?
A transient voltage surge suppressor (TVSS), commonly referred to as a TVS diode, is designed to protect electronic devices and components from overvoltage surges and electrostatic discharge (ESD) noise. It utilizes the reverse breakdown voltage characteristic of the Zener diode’s PN junction to stabilize transient voltages.
TVS diodes are favored for their excellent frequency response, offering protection against short pulse width transient voltage surges and ESD noise, which ordinary Zener diodes fail to guard against. However, they are not recommended for long pulse width surges, such as those caused by lightning. For optimal protection, they should be connected in parallel with the devices at risk of electrical overstress.
Applications of Transient Voltage Surge Suppressors
TVS diodes are utilized across a broad spectrum of applications to shield sensitive electronic equipment, data lines, and other critical devices from electrical transients. They ensure a steady output voltage in the presence of transient voltages, within the protected device’s rated voltage. Common uses include automotive and consumer electronics, where they safeguard against surge voltages within the equipment. Due to their superior frequency characteristics, TVS diodes are frequently employed in communication signal circuits.
To maximize effectiveness, TVS diodes are installed between the signal line and ground (GND) near the entry point of external noise, typically close to the board connectors where transient voltages and ESD noise usually infiltrate via the harness.
Principle of Transient Voltage Surge Suppressors
Although TVS diodes vary in design and characteristics, their primary function is to provide consistent overvoltage protection. They achieve this through high energy absorption capability, safeguarding electrical circuits from transient surges. Upon encountering an overvoltage that exceeds the diode’s reverse breakdown voltage, the TVS diode conducts current, leveraging the Zener diode’s properties to maintain voltage within safe limits, thus preventing circuit damage.
Response times differ among TVS diodes, typically around 1ps for TVS diodes and less than 1us for avalanche diodes, enabling quicker reaction to overvoltages than other components like varistors, without performance degradation over time or use.
How to Select a Transient Voltage Surge Suppressor
1. Allowable Voltage
The selected TVS diode’s allowable voltage must exceed the maximum voltage of the circuit it protects, as TVS diodes are not intended for constant current carrying.
2. Capacitance
Due to their inherent capacitive nature, TVS diodes can affect the signal’s rise and fall times by acting like capacitors under normal conditions. It’s crucial to choose a diode with a capacitance compatible with the signal specifications to preserve signal integrity.
3. Clamp Voltage
The clamp voltage should be below the maximum rated voltage of the protected device. However, the effective clamping voltage may be higher than datasheet values due to board patterns and other factors, necessitating a selection margin for clamp voltage.