3312-2mmSMDTrimmingPotentiometer

Specificationsaresubjecttochangewithoutnotice.

Thedevicecharacteristicsandparametersinthisdatasheetcananddovaryindifferentapplicationsandactualdeviceperformancemayvaryovertime.

Usersshouldverifyactualdeviceperformanceintheirspecificapplications.

2033SeriesGasDischargeTubeSurgeProtector

Optimizing Model 2033 Series Stacked GDT Turn-on Performance

Application

In high current 48 Vdc supply applications, multiple GDTs are required to be connected in series so that the sum of the arc voltages

exceed the dc supply voltage. The combined arc voltages of the stacked GDT (typically 12 V x 5 = 60 V) exceed the 48 Vdc supply

which is then not capable of providing enough current to maintain the GDT in an on-state of operation. A stacked GDT design allows

for proper reset of the GDT after a transient event.

The downside of a stacked design is that the summation of the individual GDT chamber sparkover voltages results in a device with

a high impulse sparkover voltage. For example, if each chamber of the stacked GDT had an impulse sparkover voltage of 400 V, the

total impulse sparkover for the entire GDT would be 5 x 400 V (2000 V). In many cases, this higher sparkover voltage can have a

negative impact to downstream components if their voltage sensitivity is less than the impulse sparkover of the stacked GDT.

Solution

High impulse sparkover can be improved by utilzing decoupling capacitors across 4 of 5 individual chambers of the stacked GDT.

Typical capacitor values can range from 100 pF to 1 nF.

How it Works

In its intial state, all component values are zero. Under a fast rising voltage ramp condition, there is a capacitive voltage division

across GDT1 and C1. During the voltage ramp, most of the voltage appears across GDT1. When the voltage across GDT1 reaches its

sparkover voltage (400 V), the voltage across GDT1 drops to its arc voltage which is typically around 12 V.

As a result, the capacitor is charged to a value equaling the sparkover voltage less the arc voltage (example: 400 V - 12 V = 388 V)

which is then applied to GDT2. When GDT2 reaches 400 V, it then attains sparkover and the process repeats itself until GDT5 finally

attains sparkover. This cascading turn-on mechanism of the capacitively coupled GDT chambers result in a signficantly improved

impulse sparkover voltage.

Results

In the table below, both 800 V and 1400 V stacked GDTs were compared using a 5 kV/µs voltage ramp. ITU K.12 recommends using

a linear ramp as the best method for evaluating GDT impulse sparkover under fast rising voltage conditions. Impulse sparkover

voltage limiting is signficantly improved versus using the stacked GDT discretely. It should be noted that there is some improvement in

impulse limiting by using a larger capacitor (1 nF). However, the improvement in impulse limiting must be measured against the cost of

using a larger capacitor.

C1

GDT1

GDT2

GDT3

GDT4

C2

C3

C4

C1-C4

Capacitor Values

Model 2033-80

Typical Impulse Sparkover @ 5 kV/µs

Model 2033-140

Typical Impulse Sparkover @ 5 kV/µs

No Capacitor

2200 V

2400 V

100 pF

700 V

988 V

1 nF

600 V

886 V

NOTE: Impulse sparkover in the characteristic table on Page 1 is shown under combination wave conditions (8/20 µs current/1.2x50 µs voltage).

This non-linear voltage condition will give results different than under a linear ramp speed. The typical values in the table above will differ.

Figure 1