AVR-Chat

At 05:12 PM 2/19/05 -0500, Ben Matthews wrote:
>I actually was using relays originally but the ones we could find
>couldn't deal with the current and welded quickly.


You do need a substantial relay.

>relooking at my drawing i agree that the gates are paired wrong, i do
>have it built correctly, must have been caught as i soldered it
>together.  i am going to prototype the circuit using higher voltage on
>the gates, we both thought that the mosfets would work on 5 volts or
>higher but looking at the datasheet again it makes sense although i
>have also done circuity on another vehicle using only the k2232's
>using 5 volts on the gate successfully but with out pwm and with out
>an h bridge. using the oscilloscope i have noticed some noise coming
>out of the buffer that may be turning on all four h bridge transistors
>partially, about 1.5 volts at roughly my PWM frequency.


Please note that the voltage required on the gate is referenced to the 
source so that worst case for all the BUZ11's is B+ + 10V or approx. 28V 
with a 18V battery pack!  Not only that but that potential MUST float with 
the source voltage to avoid blowing the gate when the source changes from 
18V to 0V.  It will take more than just a transistor.  Although a 
transistor may be enough for the K2232.

>Well i am going to have dinner and try it out using some small npn
>transistors suppling higer voltage to the gates,
>by the way: the data sheets:
>BUZ11's http://www.fairchildsemi.com/ds/BU/BUZ11.pdf
>the buffer: http://focus.ti.com/lit/ds/symlink/cd74hct244.pdf
>the odyssey of the mind website if any one is curious: 
>www.odysseyofthemind.com
>
>thanks for all the help so far
>Ben Matthews

You are entirely welcome Ben

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III