Various kinds of Lightning arrester circuits are available, but here describes one with Multi-level protection so any one of the component may be damaged if a strong lightning occurs. Thus it leaves the gadget without damage. Usually one Surge protector like MOV, GDT, Bidirectional Diode etc is used in surge protector circuit. But here a combination of all the three is used to give multi level protection. The circuit can be hooked up in Telephones, Cable TV lines, Modem, Dish antenna cable etc.
The circuit is straight forward. The input is the incoming lines of Telephone or cable Modem. Output goes to the Telephone instrument or Cable modem. In between the lines, there are components like a 2 Amps fuse, a 2 KV capacitor, GDT, MOV and a VDR. So each component can give protection from surge from lightning.
Lightning Arrester Circuit
680 pF 2KV Capacitor
It is high voltage ceramic capacitor that protects the instrument from very high intensity spikes.
680 pF 2 KV Ceramic Capacitor
GDT or Gas Discharge Tube, is similar to MOV (Metal Oxide Varistor) in function. It diverts the extra current from the hot line to the ground using an inert gas as the conductor between the two lines. It can be incorporated between the two lines of Telephone or between the Core (Central conductor) and the Shield (Copper clad aluminium braid shield conductor) of the coaxial cable.
GDR H230 LB
GDT functions as an on/off switch with high impedance in the normal voltage conditions. Under surge condition, its internal gas ionizes to turn the device to a low impedance state called “Arc mode or Short circuit”. In this state the GDT conducts the high voltage transients from hot line to the ground. Once the transient passes to the ground, the GDT returns to its high impedance state.
When the voltage through the cable is at a certain level, GDT will not conduct. When the voltage increases above this normal level due to a surge, the electrical power is strong enough to ionize the gas inside the GDT which act as a conductor to pass the high current to the ground until the voltage returns to the normal level. Again the GDT becomes a poor conductor.
Metal Oxide Varistor (MOV) is a Kind of VDR (Voltage Dependent Resistor) that contains a ceramic mass of Zinc oxide grains, in a matrix of other metal oxides such as small amounts of bismuth, cobalt, manganese etc. sandwiched between two metal plates which forms the electrodes. The boundary between each grain and its neighbour forms a diode junction, which allows current to flow in only one direction. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks.
MOV 431 KD 14
down due to a combination of thermionic emission and electron tunnelling, and a large current flows. Varistor can absorb part of a surge. The effect depends on the equipment and details of the selected Varistor.
The Varistor remains non-conductive as a shunt mode device during normal operation when voltage remains well below its “clamping voltage”. If a transient pulse is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed. This will blow up the Fuse and protect the device.
It is a Bidirectional Diode from Trisil which is generally used in Telephones for Bidirectional Crowbar Protection. Its voltage range is from 62 V to 270V. It is the common lightning arrestor device used in telephones which protects sensitive components in the circuit from transients voltages induced in lines from lightning.
TPA 200 Bidirectional Diode
Assemble the circuit on a common PCB or on a etched PCB and enclose inside the device. Alternately it can be enclosed in a small box with suitable telephone sockets and can be fixed outside.