>> What is the frequency of your PWM? The 754410 is happiest at 2KHz or
>> lower. At 20KHz I've detonated these chips!
When figuring pulse frequency and pulse width, you need to consider
the inductance of the motor. As you apply voltage to a winding, the
current ramps up until the core saturates and then the current is
limited only by the DC resistance of the windings. (BTW, this is why
"AC" motors are more efficient then "DC" motors.) By varying pulse
width, pulse frequency, and applied voltage you can find the "sweet
spot" for any motor.
BTW, if you have the frequency set too high you will never be able to
get the current high enough to produce the torque you need.
I am trying to figure out why the chip would have had a problem at
20KHz. I can see that the motor would not run efficiently at that
frequency but the average current and the torque would be too low.
OTOH, could you have had too much gate current in the FET switches? At
that frequency you are charging and discharging the gate capacitance
which requires more current for gate drive.
--
Brian Lloyd Granite Bay Montessori
brian AT gbmontessori DOT com 9330 Sierra College Blvd.
+1.916.367.2131 (voice) Roseville, CA 95661, USA
I fly because it releases my mind from the tyranny of petty things . . .
— Antoine de Saint-Exupéry
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PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C
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