Gas Discharge Tube Arresters (GDT)
Gas Discharge Tube Arresters (GDT) is a switching device used for circuit protection. It suppresses transient overvoltage through the principle of gas discharge and is widely used in surge protection in the fields of communication, power supply, etc.
1. What are Gas Discharge Tubes or GDTs?
1) Structural Characteristics
GDT consists of a sealed ceramic or glass tube filled with inert gas (such as argon and neon), and two or more discharge electrodes. The electrode surface is often coated with an emitter to reduce the breakdown voltage.
2) Working Principle
Normal State (untriggered): When the voltage is lower than the breakdown threshold, the GDT maintains a high impedance state (insulation resistance reaches GΩ level) and the leakage current is minimal.
Triggered State: When the overvoltage causes the inter-electrode electric field strength to exceed the gas insulation strength, the gas is ionized to form a plasma channel, and the GDT turns to low impedance (equivalent short circuit), discharging the surge current to the ground.
Recovery Characteristics: After the overvoltage disappears, the GDT automatically returns to the high impedance state without external intervention.
2. What are the Main Technical Characteristics of Gas Discharge Tubes or GDTs?
1) Electrical Parameters
Breakdown Voltage: divided into DC breakdown voltage (triggered at a slope of 100V/s) and pulse breakdown voltage (such as triggered at a slope of 100V/μs or 1kV/μs), the latter of which is usually higher.
Current Carrying Capacity: can withstand surge currents of tens of kiloamperes (8/20μs waveform).
Junction Capacitance: extremely low (usually <3pF), suitable for high-frequency signal protection.
2) Environmental Adaptability
Operating Temperature: the typical range is -40℃ to +85℃, and some models are extended to -55℃ to 125℃.
Life and Reliability: no aging failure problem, but it is recommended that the operating temperature be controlled at -40℃ to 70℃ to extend the service life.
3. Where are Gas Discharge Tubes or GDTs Used?
Communication System
As the first level of lightning protection, it discharges lightning surge currents (such as base stations and switch power lines).
Power Interface
Used with varistors, etc., to solve the problem of freewheeling and achieve multi-level protection.
High-speed Signal Line
Use low capacitance characteristics (such as less than 1pF) to reduce the impact on signal integrity.
4. Selection Considerations for Gas Discharge Tubes or GDTs
Voltage Matching
The DC breakdown voltage must be 1.5~2 times higher than the maximum operating voltage of the circuit, and the AC system is calculated as 1.4 times the effective value.
Surge Level
Select a model with flow rate adaptation according to the expected surge current (such as 10kA or 30kA).
Packaging and Installation
SMD or lead packaging, as well as environmental factors such as temperature and mechanical stress, need to be considered.
5. Product Examples of Gas Discharge Tubes or GDTs
Take TDK B88069X0680T as an example:
Nominal DC Breakdown Voltage: 90V (±20%)
Impact Current Carrying Capacity: 30kA (8/20μs)
Operating Temperature: -40℃ to 90℃, junction capacitance <1pF
GDT has become one of the core components of electromagnetic compatibility protection with its high current resistance, fast response and low leakage current characteristics.