Gas Discharge Tube (GDT) is a device that utilizes the principle of gas discharge for overvoltage protection, widely used in fields such as communication, power, and security. Its core function is to quickly conduct when overvoltage occurs, clamp the voltage within a safe range, and protect subsequent circuits from damage caused by lightning strikes, electrostatic discharge (ESD), or power surges. Here are the technical details and application analysis:
1、 Core working principle
Discharge mechanism
Initial state: The tube is filled with inert gas (such as neon or argon), and the electrodes are in a high resistance state (megaohm level).
Overvoltage trigger: When the voltage exceeds the breakdown voltage (Vbr), gas ionization forms a conductive channel, and the resistance drops sharply to the milliohm level.
Energy discharge: Transient current is discharged to ground through the discharge tube, and the clamping voltage (Vc) is limited within a safe range.
Recovery process: After the overvoltage disappears, the gas recombines and the discharge tube returns to a high resistance state.
Key Features
Low inter electrode capacitance (0.1pF~10pF), suitable for high-frequency signal protection.
Strong flow capacity (up to 100kA), suitable for high-energy pulse scenarios.
Long lifespan (able to withstand thousands of discharges), but needs to be replaced after a single use (some models support self recovery).
2、 Key technical parameters
parameter
Typical values/ranges
Key selection points
Breakdown voltage (Vbr)
75V~1000V (depending on application)
Slightly higher than the working voltage of the protected circuit (e.g. 300V Vbr for 220V system)
Clamp voltage (Vc)
100V~1500V (under 8/20 μ s waveform)
The lower the better, reducing the stress on the subsequent circuit
Flow capacity (Imax)
1kA~100kA
Need to match the surge level of the application scenario (such as 50kA or above for Level I lightning protection)
Capacitor (C)
0.1pF~10pF
The high-speed signal interface needs to choose a low capacitance model (such as<1pF)
response time
100ns
Slow than TVS/ESD tubes, but faster than varistors
3、 Mainstream types and packaging
Diode type gas discharge tube
Structure: Two electrodes are sealed inside a ceramic or glass tube and filled with inert gas.
Features: Bidirectional symmetrical protection, suitable for AC or DC circuits.
Application: Power lightning arrester, signal lightning arrester.
Triode type gas discharge tube
Structure: Three electrodes (two main electrodes and one trigger electrode), which can achieve lower breakdown voltage.
Features: Faster response time, suitable for high-frequency signal protection.
Application: Communication base station, high-frequency induction heating equipment.
Special packaged gas discharge tube
Example: Gas discharge tube with heat sink (for high-power scenarios), waterproof packaging (for outdoor applications).
4、 Typical application scenarios
Communication base station
Example: Antenna feeder lightning arrester, power supply lightning arrester.
Selection: Transistor type gas discharge tube with a current capacity of 50kA~100kA.
Industrial control
Examples: PLC, frequency converter, servo drive.
Selection: Diode type gas discharge tube with a current capacity of 10kA~20kA.
Automotive Electronics
Example: ECU, car charger, ADAS sensor.
Selection: Surface mounted gas discharge tube, certified by AEC-Q200, high temperature resistance (-55 ℃~+150 ℃).
Security monitoring
Example: Camera, network switch, access control system.
Selection: Air discharge tube, low cost, suitable for low-voltage scenarios.
5、 Core steps for selection
Determine the protective voltage
Select the breakdown voltage (Vbr) based on the operating voltage (VCC) of the protected circuit, usually Vbr=1.5 × VCC.
Example: Choose 300V~470V gas discharge tube for 220V AC circuit.
Evaluate flow capacity
Select the flow capacity (Imax) based on the application scenario:
Power lightning protection: 10kA~100kA (industrial/communication).
Signal lightning protection: 1kA~5kA (consumer electronics).
Antenna feeder lightning protection: 10kA~100kA (base station/radar).
Match signal rate
High speed interfaces (such as RS-485 and CAN bus) require the selection of ultra-low capacitance models (<1pF).
Formula: The signal attenuation caused by capacitance Δ V=I × C × Δ t, ensuring that Δ V<5% × Vswing.
Thermal Design and Reliability
Calculate energy dissipation: E=Vclamp × Ipeak × tpulse, ensuring that it is lower than the rated energy absorption capacity of the gas discharge tube.
Choose certified models (such as UL, VDE, AEC-Q200).
