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What are the power ratings of the motor ? Do you reverse the motor rapidly ? I am dealing with a DC 12 volt motor, 250 watt. Reversing control via H Drive. The peak currents at points of reversal have been measured near 50 amps for 20 ns. Dropping rapidly to quiescent levels of a few amps, load dependent. Problems seen: short burst of induced oscillation in the power FETs due to inductive spikes that turn on the FETs before Schottky diodes have a chance to kick in. Layout of board and distance to capacitive snubbers from power FET's is crucial to prevent problems.
the motor is 600W, it does not get rapidly reversed.
What are the main methods for dealing with driving inductive (motor) loads from an smps, when one has no room for a decent sized output capacitor bank?
ref your spikes turning on the fets, -sometimes you just have to use low value resistors from gate to source, and put up with their dissipation
The SMPS has limits as to the supply rails be driven above the rated output voltage and below ground. At a minimum you will want to stay within those limits, as well as current draw. When the motor starts up there will be a large current spike. When you shut the motor off you will get a large voltage spike as the inductive momentum seeks a new path to provide the motor with current. This could well result in large voltage swings below ground, for example. The usual method of dealing with the negative voltage going below ground is a Schottky diode from gnd to the power rail, sized to the motor currents. Also, application of an MOV acorss those same terminals would help this phenomena and likely could react faster than the Schottky, as the 600W motor will require a pretty healthy diode to withstand the current spikes. What is the voltage of your motor ? I am dealing with a 12V system and 250 watt motor. I see short current spikes of about 50 amps for periods of 10 to 50 nsec as the motor reverses direction. This is the time needed for the protective diodes to switch. During that period negative voltage of 2 to 5 volts can appear across the terminals that connect the motor to my controller. Does that help ?
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