TVS (Transient Voltage Suppressor) diodes are used primarily for surge protection, specifically to safeguard sensitive electronic components from damaging voltage spikes. They are essential defense mechanisms in electronic circuits against unpredictable and potentially destructive transient overvoltages.
As stated by RS Components, TVS diodes are components that are used to protect sensitive components such as semiconductors. They are designed to react to Voltage spikes and clamp the Voltage at a set amount before going into the circuit.
The Threat: Voltage Spikes (Transients)
Electronic circuits, especially those containing sensitive semiconductor devices like microcontrollers, integrated circuits (ICs), and data line interfaces, can be severely damaged by sudden, high-energy voltage surges. These transients can originate from various sources:
- Lightning strikes: Induced voltages on power or communication lines.
- Inductive load switching: Motors, relays, or transformers being switched on or off can create back EMF spikes.
- Electrostatic Discharge (ESD): Static electricity buildup discharging into a circuit.
- Power supply fluctuations: Surges on AC or DC power lines.
These spikes can momentary exceed the normal operating voltage of components by hundreds or even thousands of volts, leading to immediate destruction or degradation over time.
The Solution: How TVS Diodes Protect
The TVS diode provides protection by offering a very low impedance path to ground (or another rail) when the voltage across it exceeds its specified breakdown voltage (VBR).
- Under normal operating voltages: The TVS diode presents a very high impedance, essentially acting as an open circuit and having minimal effect on the signal or power line.
- During a voltage spike: When the transient voltage rises above the TVS diode's breakdown voltage, the diode rapidly switches into a low-impedance state. This action diverts the vast majority of the surge current away from the protected component and shunts it to ground.
- Clamping: The diode "clamps" the voltage across the protected circuit to a safe, predetermined level (the clamping voltage, VCL), which is typically just slightly above the normal operating voltage. This prevents the damaging high voltage from reaching the sensitive components downstream.
This process happens incredibly fast, often within picoseconds, making TVS diodes highly effective at responding to fast-rising transient events like ESD.
Here's a simple illustration of the TVS diode's function:
| Condition | Voltage Across TVS | TVS Diode State | Voltage Reaching Protected Circuit | Outcome |
|---|---|---|---|---|
| Normal | Below VBR | High Impedance (Off) | Passes Through Freely | No Impact |
| Voltage Spike | Above VBR | Low Impedance (On) | Clamped to Safe Level (VCL) | Protection |
Protecting Sensitive Components
As mentioned in the reference, TVS diodes are crucial for protecting sensitive components such as semiconductors. Modern semiconductors, especially those built with smaller process technologies, are increasingly vulnerable to overvoltage events due to their delicate internal structures.
Common applications where TVS diodes are used include:
- Protecting I/O ports (USB, Ethernet, RS-485, etc.) from external transients.
- Safeguarding power supply inputs from line surges.
- Protecting data and signal lines within a circuit.
- Providing ESD protection on user interfaces.
In essence, the TVS diode acts as an electronic 'safety valve', sacrificing itself if necessary to protect the more valuable and complex components it guards from the harmful effects of voltage spikes.
