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Re: [TCML] SCR turn off spike



Chris Swinson wrote:
Hi all,

I noticed in my scope waveform a negative spike on the SCR gate, image....
http://www.future-technologies.co.uk/IMPULSE/newcoilprog/new/scrpulse2.jpg

I wonder if I should add some protection on the gate as I am worried the spike will damage the gate if left in that state. I don't have any specs on the SCR so I don't know what is the safe operating area for it. #

Going by a similar sized SCR, it says max positive voltage 20V and max negative voltage 5V. I am hitting 5V negative just on 5VDC input (20V on the SCR).

Cheers,
Chris

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Hi Chris,

Are you connecting a short ground connection from the tip end your oscilloscope probe to the circuit you're measuring? If not, fast the rising/falling logic signals will cause ringing artifacts. Your scope waveform shows an even larger positive spike, and both spikes look like they may simply be measurement artifacts. In any event, SCR's are pretty robust - as long as you don't use excessive gate drive current you should be fine.

Bert
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