| 摘要 |
Overvoltage protection devices operative to prevent damage to electrical equipment in response to overvoltages in the form of fast transients and also to continuous overvoltages utilizes clamping or discharge elements which conduct in response to overvoltages or current surges. A high voltage responsive element, suitably a spark gap, is connected to the input of the device which goes to the line, while a lower voltage responsive element, suitably an avalanche diode or diodes or a zener diode or diodes, is connected to the output of the device which goes to the equipment to be protected. A resistor is connected between the spark gap and the avalanche device in series with one side of the line on the circuit to be protected. This resistor is preferably a positive temperature coefficient resistor which changes resistance rapidly to a high resistance state when the avalanche device conducts so as to protect the avalanche device while allowing the development of overvoltages sufficient to cause breakdown and conduction in the spark gap. Fast overvoltage transients are protected against by inductance between the avalanche device and the output that is greater than the inductance in the shunt path provided by the avalanche device.
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