Re: stand-off voltage of zener TVS device for a relay coil



Matt wrote:

I'm switching a 5VDC relay coil using a FET and a microcontroller.

I'm comfortable using a bidirectional transient voltage suppressor
(which functions like two zener diodes back-to-back) across the
coil---except for a little issue with the stand-off voltage. I think
that that is supposed to be the normal operating voltage of the device
(in this case 5V). The stand-off leakage current seems to be the
current when the device is run at the stand-off voltage (800uA for the
5V device).
(cf. http://www.fairchildsemi.com/ds/SM%2FSMBJ20A.pdf)
That doc also mentions a "test current" of 10mA. I'm guessing that that
is what defines the clamping voltage.

It looks like it.


Am I understanding these parts of the data***?

If you want your relay to 'snap' open you'll have to use a higher voltage part
than that though.

Graham

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