<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=US-ASCII">
<META content="MSHTML 6.00.6000.16587" name=GENERATOR></HEAD>
<BODY id=role_body style="FONT-SIZE: 10pt; COLOR: #000000; FONT-FAMILY: Arial"
bottomMargin=7 leftMargin=7 topMargin=7 rightMargin=7><FONT id=role_document
face=Arial color=#000000 size=2>
<DIV>Hey Chuck,</DIV>
<DIV> </DIV>
<DIV>Thanks for more explanation.</DIV>
<DIV>I found your ASCII art worked good once went to non-proportional
font.</DIV>
<DIV>Will read again.</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>I fired up LTspice/SwitcherCAD and figured out how to use the program sort
of.</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>I think I am seeing ground bounce as you describe it with ground connected
as shown.</DIV>
<DIV>I have turned off (via large resistors) most of the capacitive filtering in
the example circuit.</DIV>
<DIV>I am clamping (to some extent) the flyback of the motor inductor, but the
ground inductance is allowed to generate a voltage which counters MCU supply by
pushing "ground" up -- if I said that correctly.</DIV>
<DIV> </DIV>
<DIV>Here are pics of schematic and plot...</DIV>
<DIV> </DIV>
<DIV>http://<A
href="http://www.deltagr.com/dprg/DualBatMotorSwitch.jpg">www.deltagr.com/dprg/DualBatMotorSwitch.jpg</A></DIV>
<DIV><A
href="http://www.deltagr.com/dprg/MotorSim.jpg">http://www.deltagr.com/dprg/MotorSim.jpg</A></DIV>
<DIV> </DIV>
<DIV>Ignore first cycle on graph -- not sure why not doing correct analysis on
that -- told it something...</DIV>
<DIV> </DIV>
<DIV>My schematic is prettier than yours!, but I just spent TOO much time
figuring out how to use the simulation tool again.</DIV>
<DIV> </DIV>
<DIV>I know simulation is only as good as person designing it, but I have
learned a good deal I think.</DIV>
<DIV> </DIV>
<DIV>I can see grounds with large inductances can produce some pretty wicked
voltages -- if I was doing things right. Without capacitor filter -- some pretty
wicked voltages... looks like one could toast a MOSFET ....</DIV>
<DIV> </DIV>
<DIV>Hope I am getting it...</DIV>
<DIV> </DIV>
<DIV>Ron</DIV>
<DIV> </DIV></FONT><BR><BR><BR><DIV><FONT style="color: black; font: normal 10pt ARIAL, SAN-SERIF;"><HR style="MARGIN-TOP: 10px">Start the year off right. <A title="http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489" href="http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489" target="_blank">Easy ways to stay in shape</A> in the new year. </FONT></DIV></BODY></HTML>