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Original question:

LM555: 12V, 3A Power switch with timer function.

LM555: LM555 sometimes dead

user4937122
Prodigy 120 points
Part Number: LM555

Dear Sir.

I tested the circuit below.

The load is a filament heater with 3.3Ohm, 

but the LM555 timer was sometimes dead and LED was burnt.

Could you check what is problem with this circit ?

Best Regards,Yoon.

  • 0
    TI__Mastermind 23965 points

    Yoon,

    My suspicion is inductive kickback from the heating element. Although it is a resistive element, they are generally made of wound coils which also look like an inductor. In this case adding a transient voltage suppression diode (TVS diode) to the supply line could help with this scenario.  

    We have a series on EOS. If you look to the right of this link you will see 4 videos 12.1 through 12.4 that will walk you through these events and choosing components for protection.

    https://training.ti.com/node/1138807

  • 0 in reply to Chris Featherstone
    Prodigy 120 points

    Dear Chris.

    Thank you so much !

    After checking 12.1~4. I applied some TVS to my circuit.

    Best Regards,Yoon.