I have an ATTiny85 design that I power from a 24VDC wall wart. My circuit has an LDO generating 5VDC from the 24VDC (there are no other active components on the 5V rail so there's not a lot of power dissipated in the LDO). The Tiny controls a MOSFET which controls a 24VDC solenoid. When I plug the cable from the wall wart into my board I get a spike on the 5V rail that sometimes exceeds 8V (though just for a few microseconds). Enough of this finds its way to the IO pins to trigger the gate on the MOSFET, triggering the solenoid when I don't want it to be triggered. I've tried a range of caps on the 5V rail and the specific IO line in question, from .01 uf up to .1 uf, but without consistently reliable results. Any suggestions for how to filter out this spike? Thanks.
Joined: Tue. Apr 1, 2003
Posts: 485 View posts