Talon vs. Talon SR

[Ether]

Originally Posted by omalleyj

Can someone explain (to a simple programmer) the difference between the Talon and Talon SR?
What is the practical difference between "Locked Antiphase Rectification" and Synchronous Sign Magnitude Rectification"?
Was the change made to address any specific problem or application?
TIA

from the Web:

http://danstrother.com/2011/01/12/br...troller-board/

locked-antiphase allows for regenerative braking. Unfortunately, the low inductance of most brushless R/C car motors results in very quick current changes in the phase windings. Since locked-antiphase depends on the winding inductance to smooth out and reduce circulating/ripple current, this was a major problem; at reasonable PWM frequencies, the ripple current was very high – while, at high PWM frequencies, the MOSFET switching losses were unacceptable.

Switching to sign/magnitude resolves most of those issues, but introduces some of its own. Most importantly, the body-diode on the MOSFETs must now come into play during PWM off-cycles. The body diode is a lot higher loss than the MOSFET, so it results in more power dissipation. Synchronous rectification would help with this, but would be tricky to implement in firmware (especially given the rapid current decay rate). Many dedicated motor controller ICs have integrated hardware for implementing synchronous rectification.


http://www.openservo.com/forums/viewtopic.php?t=142

Locked-antiphase PWM is somewhat counter-intuitive and at first seems like it would just burn up a lot of power. The motor is alternately driven forward and then reverse; this actually works because the motor's inductance low pass filters the current to a DC value. At 50% duty cycle the average current is zero, and so the motor remains stopped. Increase the duty cycle and the average current becomes positive and the motor turns "forward".

Of course, the motor isn't a perfect low pass filter, and the resulting waveform will have ripple. If the motor has too little inductance for the PWM frequency used, then there will be a lot of ripple and the power loss will go up. You'll also be able to feel vibration in the motor when it is stopped.