On 03.05.16 10:30, andy pugh wrote: > And does the "fail to turn off" problem description include not > turning off ever again, even when removed from the circuit and from > all power?
No, dv/dt triggering is merely spurious initiation of conduction by excessively rapid increase of applied voltage, without gate current being applied. An SCR (thyristor) is a four-layer diode, electrically equivalent to a PNP and NPN transistor stacked into a totem feedback pair, and once it starts to conduct, it latches on - while there's more than its holding current flowing. It is not going to happen with rapidly decreasing voltage, AIUI. In fact, if you connect two SCRs, each with a resistor in the anode circuit, across a DC supply, then interconnect the anodes with an adequately sized nonpolarised capacitor, and one SCR is conducting, then triggering the other will switch off the first. My suspicion is that the device failure is likely due to the 40v margin on the mains peak voltage not being adequate. In a machine environment, with heavy inductive loads being switched, it might be instructive to try a 600v SSR, and compare lifetimes. If the overvoltage is due to an inductive load on the SSR, then a flyback diode will fix it if the circuit is DC, otherwise a snubber can absorb the spike energy. (A snubber is just a series RC combination, with the resistor low enough in value to limit the spike amplitude, but high enough not to run hot normally, and with the capacitor large enough to be a low impedance to the spike's dv/dt, but high enough at 50 Hz for the resistor not to run hot normally, at least that's my grasp of it.) Erik ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
