Re: My Battery Monitor

["Eric Chang" <ericchang@my-deja.com>]

>Is was wondering if anyone had used, considered
>or had an opinion about TOPFETs (Phillips semiconductors) and PROFETs
>(Siemens semiconductors).

Try drawing a simple circuit for accomplishing this.  You will find
some problems with gate drive and common mode voltages.

Here is a partial circuit diagram to get you started:

*Batteries and FETS
.subckt onecell minus plus mminus mplus
vb1 plus minus dc 12
m1 mminus g1 minus nmos
m2 mplus g2 plus nmos
vsw1 g1 minus DC 15
vsw2 g2 plus DC 15
.ends

xbat1 t0 t1 mm mp
xbat2 t1 t2 mm mp
xbat3 t2 t3 mm mp
...
rmeter mm mp 1000000

If you attempt to drive the inner nodes for turning on one monitor
with the same voltage source, there will be trouble, since you will
not maintain the requisite 15 volts.  If you do it with two isolated
power supplies per subckt, it will work but it will be expensive.

Now, flatten the netlist and look at all the instances of m1.  You
will see that the voltage limit of your parts choices are exceeded
with a not very large stack of batteries.

A picture would help a lot, a burnt out MOSFET would help even more,
but it is hard to show those on the list due to restricitons.









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