Metal oxide varistors typically have lower resistance as they heat up; if connected directly across a power bus, for protection against electrical transients, a varistor with a lowered trigger voltage can slide into catastrophic thermal runaway and sometimes a small explosion or fire.
22.
In the case of a varistor, how do its parameters such as maximum energy and maximum continuous voltage vary when you convert a through hole varistor to an SMD ? thank you . blah blah ) 07 : 13, 14 March 2007 ( UTC )]
23.
In the case of a varistor, how do its parameters such as maximum energy and maximum continuous voltage vary when you convert a through hole varistor to an SMD ? thank you . blah blah ) 07 : 13, 14 March 2007 ( UTC )]
24.
Power ratings might vary a bit but I'd imagine they'd vary just as much depending on the lay-up of the PCB; soldering the varistor leads into / onto massive ground or power planes would obviously have some positive benefit to the long-term power rating although the impulse rating probably wouldn't change noticeable.
25.
A varistor provides no equipment protection from inrush current surges ( during equipment startup ), from overcurrent ( created by a short circuit ), or from voltage sags ( also known as a power disturbances is defined by other aspects of the system design, either inside the equipment itself or externally by means such as a UPS, a voltage regulator or a surge protector with built-in overvoltage protection ( which typically consists of a voltage-sensing circuit and a relay for disconnecting the AC input when the voltage reaches a danger threshold ).
26.
In my case, the maximum continuous voltage of my through-hole varistor is 275Vdc and its maximum energy is 104J . I've looked up to the internet looking for SMD Varistors with the same or even almost equivalent parameters but the maximum contiuous vaoltage that I saw was around 56Vdc and worse for the maximum energy, the highest value that I got was 1.5J . that is why I was thinking that maybe some of the parameters of a varistor would be changed when it is " converted " from through-hole to SMD.
27.
In my case, the maximum continuous voltage of my through-hole varistor is 275Vdc and its maximum energy is 104J . I've looked up to the internet looking for SMD Varistors with the same or even almost equivalent parameters but the maximum contiuous vaoltage that I saw was around 56Vdc and worse for the maximum energy, the highest value that I got was 1.5J . that is why I was thinking that maybe some of the parameters of a varistor would be changed when it is " converted " from through-hole to SMD.
