Transient Voltage Suppressor Diodes: Understanding The Working Of TVS Diode

 

Transient Voltage Suppressor Diodes

What are Transient Voltage Suppressor Diodes?

Transient voltage suppressor (TVS) diodes are electronic components that protect other circuit elements from voltage spikes and surges. They act as a clamp or limit on the maximum voltage that can appear across certain terminals of a circuit.

Working Mechanism of TVS Diodes

TVS diodes make use of the inherent properties of semiconductor junctions to clamp or limit voltages. When a semiconductor junction is forward biased, it allows current to flow easily. But when reversed biased, it presents a high resistance to current flow.

Normally a Transient Voltage Suppressor Diodes presents a high resistance to low voltages as its junction is reversed biased. But beyond a certain threshold voltage known as the breakover or strike voltage, the junction suddenly switches to a low resistance state as it becomes forward biased.

This allows heavy current from voltage spikes and surges to flow through the diode instead of into the protected circuit. The excess energy is dissipated harmlessly as heat through the diode. Thus TVS diodes act as path of least resistance to divert transient overvoltages and shield other components.

Types of TVS Diodes

TVS diodes come in different types depending on the required protection level, waveform characteristics of the transients etc. Some common TVS diode types are:

- Unidirectional TVS Diodes: As the name suggests, these allow current flow in only one direction making them suitable for protecting against positive or negative going transients but not both.

- Bidirectional TVS Diodes: Capable of conducting current pulses in both directions, they can protect against voltage spikes of either polarity. Used where transients can occur with either positive or negative orientation of the overvoltage.

- High-Energy Surge Diodes: Designed to withstand very high transient energy levels of several joules or more. Used to protect equipment against direct or indirect lightning strikes and other high intensity disturbances.

- Low-Capacitance TVS Diodes: Have minimized stray capacitance for protecting high frequency or high speed circuits against noise or voltage spikes without impairing their operating bandwidth or speed.

- High-Temperature TVS Diodes: Capable of operating at raised ambient temperatures up to 150°C or higher. Useful in applications installed in locations prone to high temperatures.

Parameters of TVS Diodes

Some key parameters that determine the transient handling capability and characteristics of a TVS diode are:

- Breakover or Strike Voltage (VBR): The minimum voltage at/beyond which the diode switches to a low impedance state and starts conducting current.

- Maximum Repetitive Peak Pulse Current (IPPM): Highest non-destructive current the TVS diode can pass during consecutive voltage pulse transients. Defines its surge current rating.

- Maximum Clamping Voltage (VCL): The voltage across the TVS diode once it has switched on and is conducting current during a transient event. Defines the clamping level.

- Capacitance (Ct): The inherent junction capacitance of the TVS diode. Should be minimized for high frequency applications to avoid signal degradation.

- Response Time (trr): Time taken by the TVS diode to switch from high to low impedance state after the transient voltage exceeds VBR. Faster times provide better protection.

- Energy Dissipation Capability: The amount of transient energy a TVS diode can safely absorb during repeated current surges without damage. Defined in joules.

The combination of these parameters along with waveform characteristics of the transients to be protected against help determine the appropriate TVS diode selection for a given application.

Applications of TVS Diodes

Some common applications where TVS diodes are widely used for transient voltage protection include:

- Telecommunications Equipment: Used to protect telephone lines, network interface units, modems etc. from high voltage spikes and lightning induced transients.

- Power Supplies: Placed at the input and output of AC-DC power adapters and supplies to suppress noise and surges originating both externally and internally.

- Automotive Electronics: Employed in engines control units, infotainment systems, sensors and other automotive electronic control modules to shield against load dump transients.

- Industrial Equipment: Deployed for protecting low voltage I/O lines of PLCs, frequency converters, motor drives etc. entering or leaving industrial factory floors.

- Home Appliances: Used in appliances like washing machines, refrigerators, ACs etc. to safeguard internal electronic circuits from mains borne transients and noise.

- I/O Port Protection: TVS diodes placed point-of-entry at interface I/O ports of computers, industrial controllers, communications equipment offers surge protection.

- Personal Electronics: Found in power supplies, chargers and interface ports of consumer gadgets like smartphones, laptops etc. to bolster ESD and surge robustness.

Transient voltage suppressor diodes provide a simple, low cost and effective solution for suppressing transient overvoltages and shielding sensitive electronic circuits across a wide range of applications. Their deployment has become almost ubiquitous in many commercial and industrial products containing electronic control systems.

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