gas discharge tubes (gdt) training material construction and characteristics of gdts performance...

Gas Discharge Tubes (GDT) Training Material

Construction and Characteristics of GDTs

Performance Ratings

Selection of GDT for Application

Applications when NOT to use GDTs

Comparison of Protective Devices

Gas Discharge Tubes

A bolt of lightning flashes through the sky and hits the ground somewhere around the world about 100 times every second. That’s 8 million lightning strikes in a single day!

Scientific America- Nov 2014 – Global Warming: New findings suggest lightning strikes may increase by 12% for every degree (°C) of warming … That comes to a 50% increase (in number of lighting strikes) by the end of the century

Gas discharge tubes (GDTs) are ideal for lightning surge protection of electronic equipment, as GDTs can dissipate

large amounts of energy in small size components

Gas discharge tubes (GDTs) are ideal for lightning surge protection of electronic equipment, as GDTs can dissipate

large amounts of energy in small size components

Why are Gas Discharge Tubes

needed?

Electrode

Solder

Ceramic Tube

Gas

Electrode

Carbon line

Ceramic Tube

Electron emission material

Solder

Construction of GDTs

Gas Discharge Tubes

Gas discharge tubes by nature of their construction can handle very large amounts of current, are bidirectional. They have very high impedance and low capacitance, resulting in very little current leakage or signal loss. So the GDT is ‘virtually invisible’ to the protect circuit. GDTs are normally used as primary protection devices, in conjunction with other kinds of protect devices (with faster response speed) as secondary protection. When a surge voltage reaches the GDT spark-over voltage, the GDT will switch into virtual short, divert the surge current through the GDT to ground and removing the voltage surge from damaging the equipment. Therefore, GDTs provide excellent protection during the time period that they are active.

The Townsend discharge is a gas ionization process where free electrons, accelerated by a sufficiently strong electric field, give rise to electrical conduction through a gas by avalanche multiplication, called an Townsend Avalanche. An electron avalanche is a process in which a number of free electrons in a transmission medium (gas) are subjected to strong acceleration by an electric field and subsequently collide with other atoms of the medium, thereby ionizing them (impact ionization). This releases additional electrons which accelerate and collide with further atoms, releasing more electrons—a chain reaction. In a gas, this causes the affected region to become an electrically conductive plasma. The avalanche effect was discovered by John Sealy Townsend in his work between 1897 and 1901, and is also known as the Townsend discharge.

Visualization of a Townsend

Avalanche*

Characteristics of GDTs

Gas Discharge Tubes

Gas Discharge Tubes

Voltage

Current

Standoff Resistance

Gas Discharge

Tube

Gas Discharge Tubes

Typical GDT specification sheet

The following is a review of the GDT specifications

DC Breakdown & Spark-over Voltage

SELECTION GUIDE:With the same DC Breakdown Voltage, the lower the Impulse Spark-Over Voltage, the faster the response speed and the better protection

Part Number

DC Breakdown

Voltage(100V/s)

Breakdown Voltage

Tolerance(V)

ImpulseSpark-Over

Voltage(1KV/μS)

NGTA1812N401TR1F 400V 340~550 ≤750V

NGTC1812N401TR1F 400V 360~560 ≤950V

Better protection; lower impulse voltage = faster response

Slower response

The curves (left) show the typical DC breakdown voltage (100V/S) and Impulse Spark-over Voltage (1000V/uS) of NGTA series GDT

Gas Discharge Tubes

Selected based upon operating voltage level (VDC)

The value of Impulse Spark-over Voltage reflects the Gas Discharge

Tube response speed

The arc voltage is developed across the GDT during its “virtual short circuit” condition. This parameter defines the power dissipation of the GDT during its protection mode.

GUIDE: A low arc voltage is desirable to keep power dissipation at a minimum, which in turn increases the life expectancy of the gas discharge tube.

Higher power dissipation (higher operation temperature) will act to reduce the lifetime of the gas discharge tube.

Arc voltage under AC voltage condition

Voltage

Current

Gas Discharge Tubes – Arc Voltage

The voltage developed across the GDT component when it is operating is called the “Arc Voltage“ ( Va in above example )

The voltage developed across the GDT component when it is operating is called the “Arc Voltage“ ( Va in above example )

Low Arc Voltage of GDT construction makes the GDT ideal protection against lightning (high-energy) and AC line overvoltage conditions

Solution BSolution A

48VDC solution

Examples: Two solutions (A & B) for 48VDC power port, solution A (above left) uses a special 5-element, 6-terminal GDT. The Arc voltage is >60V@1A, higher than 48VDC, so it is safe choice. Solution B (above right) use a lower voltage single GDT (PN: NGTF2016M091TR5F) in series with a MOV, because the arc voltage of NGTF2016M091TR5F is about 8V@1A, which is lower than the 48VDC system voltage, so it needs to be used in series with a MOV which will claim above 48VDC


While low Arc Voltage is desired to minimize power dissipation, the Arc voltage of the GDT in DC circuits should be above the operating voltage level to assure turn off of the GDT. When GDT is used to protect 48VDC power port, the

arc voltage of the gas discharge tube should be selected to be higher than the operating voltage, as shown in Solution ‘A’ below, or used in series with a MOV (such as NIC NVR series) as shown in Solution ‘B’ below

NGTA1812N301TR1FNGTA1812N401TR1F

NGTF2016M351TR5FNGTF2016M801TR3FNGTF2016M102TR3FNGTF2016M122TR3F

NGTM2332M351TR20FNGTM2332M471TR20FNGTM2332M601TR20FNGTM2332M801TR20FNGTM2332M152TR10FNGTM2332M362TR10F

NGTD3020M231TR5FNGTD3020M102TR5F

15V 15V 15V 15V

DC12VAC24V

DC12VAC24V

DC12VAC24V

DC12VAC24V

NIC has developed Higher Arc Voltage GDTs, which can be applied in higher voltage DC/AC applications

Format

Part Number

Application

Arc Voltage

Arc Voltage at 1A


NGTA / NGTC (4.5x3.2x2.7)

NGTD (7.6x5x5) Custom (24.1x8.3x9.2) Custom (16.5x8.3x9.5 & 19.9x8.3x9.3)

NGTF (4.2x5x5) NGTM (6x8.3x8.3)

High Surge Current rating is one of the main characteristic of GDTs. NIC can provide surge current rating: 1KA ~ 20KA @ 8/20uS in single and multiple element construction

GDT suggested as the primary circuit protection, due to its high surge current rating performance.

Gas Discharge Tubes - Surge Current

1KA / 2KA 5KA

5KA 20KA 20KA

20KA

Single Element

Construction

Multiple Element

Construction(2, 4, 5)

Series Typical Capacitance Value

NGTA 0.26pF

NGTC 0.26pF

NGTD 0.57pF

NGTF 0.48pF

NGTM 0.98pF

Another characteristic of GDT is capacitance value, which is very important for data signal transfer, especially for high speed - frequency (lower capacitance = less signal loss).

NIC provides GDTs with very low capacitance as shown below.

Typical Capacitance value @1MHz

Gas Discharge Tubes

SELECTION GUIDE:To protect high speed applications, the protection device must have low capacitance values

Silicon Avalanche Suppressors, MOVs & Transzorbs can have >100pF capacitance value

Parameters - Characteristics of GDTs

Gas Discharge Tubes

Lower is betterLower is better

Higher is betterHigher is better

Selection based upon operating voltage Selection based upon operating voltage Guidance based upon application

VAC or VDC

Guidance based upon application

VAC or VDC

GDT Selection

GDT selection

When used to protect power port, Arc Voltage must be higher than the peak value of the supply voltage

DC Breakdown Voltage

Must be higher than the peak work voltage of the protective circuit

It must be higher than the highest surge current of the protected circuit

Impulse Spark-over Voltage

Must be lower than the highest voltage the protected circuit can allow

Arc Voltage Surge Current Rating

Gas Discharge Tubes

GDTs are suggested for use in primary protection, but not suggested for use in secondary or ESD protectionGDTs are suggested for use in primary protection, but not suggested for use in secondary or ESD protection

Primary Protection:GDT

Example: Tip & Ring xDSL protection solution

Low response speed

High residual voltage

High surge current rating Good for large surge current protection Use in primary protection

Not suggested for fine protectionNot used in secondary or ESD protection

Gas Discharge Tubes

Secondary or ESD Protection TVS

GDTArc voltage 15V@1A

12VDC solution

L

+12V

0V

Gas Discharge Tubes

When GDT is used in power port, need to be cautious in selection of GDT. Must ensure the GDT can shut off after surge wave has passed. The arc voltage of the GDT should be

selected higher than the circuit voltage, or use the GDT in series with a MOV.

When GDT is used in power port, need to be cautious in selection of GDT. Must ensure the GDT can shut off after surge wave has passed. The arc voltage of the GDT should be

selected higher than the circuit voltage, or use the GDT in series with a MOV.

Secondary Protection TVS

GDT – Gas Discharge Tube

TSS - Thyristor Surge Suppressors

TVS - Transient Voltage Suppressor

MOV - Metal Oxide Varistor

Operating Principle

Gas discharge Avalanche effect of PN junction

Avalanche effect of PN junction

Nonlinear voltage characteristic

Protection Mode

Switch Mode Switch Mode Clamp Mode Clamp Mode

Response speed Slow Fast Very fast Medium

Ability of withstand high

voltageHigh Medium Low Medium--High

Leakage Very low <5uA <5-10uA <20-30uA

Capacitance Very low, normally lower than 1pF

Mid (be related to lightning level)

Mid (be related to lightning level)

Large (be relate to the size and

lighting level)

Failure Mode Open Short Short Short

DeviceDeviceItemItem

Comparison of Over-Voltage Protective Devices

Switch Mode

Clamp Mode

TVS - Transient Voltage

Suppressor


TSS - Thyristor

Surge Suppressor

GDT – Gas Discharge

Tube



GDT – Gas Discharge Tube

TSS - Thyristor Surge Suppressors

TVS - Transient Voltage Suppressor


Advantage

High Surge Current Rating,

Low Capacitance, Low Leakage

Low Residual Voltage, Fast Response Speed,

High Accuracy of Voltage

Low Residual Voltage, Fast Response

Speed, High Accuracy of

Voltage

High Accuracy of Voltage,

Low cost

Disadvantage High Residual Voltage, Slower Response Speed

Limited Voltage Range,

Can Not Be Used In Power supply Port

Low Surge Current Rating,

Unit cost increases with Surge Current

Rating Increase

High Capacitance,Easy Degenerate,

Large Leakage

Typical Usage Applications

Mainly used to primary protection of signal ports with high flow capability

or low voltage power supply ports

Mainly used primary or secondary protection of

signal ports, Normally not used in power supply ports

Mainly used for fine protection, such as

secondary, third level protection and ESD

protection

Mainly used in power supply ports, normally not used in signal ports

due to its’ high capacitance.

NGTA / NGTC (4.5x3.2x2.7) NGTD (7.6x5x5)NGTF (4.2x5x5) NGTM (6x8.3x8.3)

NIC SMT Gas Discharge Tubes

SMT Format: Single Element Construction & 2-Element Construction

Series Size BreakdownVoltage Current

Impulse Spark-over

Voltage

NGTA 1812 150V 400V 1KA 650V 750V

NGTC 1812 200V 600V 2KA 700V 1200V

NGTD 3020 90V 1000V 2KA & 5KA 700V 1800V

NGTF 2016 90V 1200V 3KA & 5KA 650V 2000V

NGTM 2332 90V 3600V 5KA 20KA 600V 5000V

Featuring: Ultra High Current, Low Capacitance & Low Insertion LossQVGQ2.E467518 / E467518

Isolated Loop Circuit Protectors – Component, Transient-voltage

surge suppressors, gas tube

NIC SMT Gas Discharge Tubes

Gas Discharge Tubes Applications Power Supply Voltage Protection ADSL, xDSL Applications General Telecommunication Equipment CATV & Satellite Applications Communications Equipment Smart Metering, Green Power Data Transmission Line - Port Protection:

RS485 RS232 xDSL Ethernet

NIC Circuit Protection Products

NFVC Series Chip Fuse

Over-current Protection

NPX Series X2 CapacitorInterference Suppression

NVR Series Metal Oxide Varistor (MOV)Over-voltage protection

NGT_ Series Gas Discharge TubesOver-voltage Protection

NIC Circuit Protection Products→ NGT_ - SMT Gas Discharge Tubes→ NVR – MOV High Voltage Varistors→ NPX– X2 Safety Capacitors→ NFVC – 125V / 250VAC Chip Fuses

NIC Circuit Protection Products→ NGT_ - SMT Gas Discharge Tubes→ NVR – MOV High Voltage Varistors→ NPX– X2 Safety Capacitors→ NFVC – 125V / 250VAC Chip Fuses

Additional Information Needed?Need Samples?

Additional Information Needed?Need Samples?

NIC Components offers unique performance passive components that provide advantages to design engineers to create high performance end products in smaller and lower total cost formats

• Surface Mount SMT formats (high speed auto placement)• Pb-Free Reflow Compatible (high temperature reflow) • Performance advantages over competing technologies

Technical Support: [email protected]

Sales Support: [email protected]

Technical Support: [email protected]

Sales Support: [email protected]

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