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Need DC Solid State Relay Latch Up advise

I have a latch up issue with a pair of DC solid state relays that I need some advise. The two relays used are DC Tyco DS13-1000 (1 A) style relays. The outputs are tied in parallel with the Pos term connected to

+28V and the Neg term connected to a 70 ohm load resistor. Each control input are is independently controlled.

I'll describe the behavior in steps:

1) K1 is ON/ K2 is OFF - I1 flow through K1 (400mA) 2) K1 is OFF/K2 is OFF - I1 ceases within 100uSec (Turn off time of K1) 3) Wait ~160 uSec (This is an inherent delay in the circuit i.e not by design) 4) K1 is OFF/K2 is ON - I2 does NOT flow - K2 latched up.

I should mention that if the delay #3 is increased to > 2mSec or so, the issue does not occur. Also, if K1 is left on while K2 is switched ON then turning K1 OFF, the latch up does not occur.

I realize that there are turn-off and turn-on times with the relays but why would this cause one of the solid state to latch up? Obviously, adding additional delay between switching would resolve the problem but I am attempting to understand the latch up mechanism. Thanks for any advice you may have. Jim

Reply to
Jim Flanagan
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Datasheet:

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When you turn off SSR #1, SSR #2 sees a high dv/dt across its terminals. Maybe you're tripping SSR #2's overload protection?

"The overload feature provides protection of the relay, load and load circuit wiring in the event of a sustained current over- load or short circuit while the relay is on or when it is turned on into a short."

Cheers, James Arthur

Reply to
dagmargoodboat

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