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Pancake Resolvers >> Brush Type Motors >> Brushless DC Motors +V S S1 +V S S2 +V S S3 Direction Control Input PWM INPUT FROM VELOCITY CONTROL CIRCUIT portional to the input control voltage.The same control scheme can be applied to a three phase brushless DC torque motor as shown in Figure 10. The Hall devices are mechanically displaced 120 electrical degrees from each other and are aligned with the BEMF waveform of each phase.The control equations are as previously derived for the two phase system, except the output torque is: T = VC KC (Sin2 + Sin2 (0 + 120) + Sin2 ( - 240)) T = 1.5 VC KC and, as before, the output torque is directly proportional to the input control voltage. Square Wave Drive A square wave drive system provides the most efficient utilization of the control elec- +V S PROM or Custom I.C. (800) 777-3393 tronics, and yields the lowest system cost. Power dissipation in the output stage is minimized by operating the power switch devices in the complete OFF or fully ON stage.The output stage can be interfaced directly with the commutation logic circuit, and the whole system can be digital. This allows the use of lower cost digital integrated circuits to decode the position sensor output and to sequence the drive circuit power semiconductors. Figure 11 shows a simplified drive circuit for bi-directional control of a two phase brushless DC motor.The timing and excitation waveform for this motor were shown in Figure 7.The rotor position sensors are Hall effect switches and their outputs are processed by Exclusive OR gates. This feature allows the direction of rotation to be reversed. A logic “1” on the direction con- www.axsys.com > Q1 +V S Q2 Q3 Q4 Q5 Q6 CURRENT SENSE OUTPUT Figure-13. Functional drive circuit for bi-directional control of a three phase brushless DC motor. 0B 0A 0C Commutating Brushless DC Motors
Commutating Brushless DC Motors (800) 777-3393 +V S S1 +V S S2 +V S S3 PWM INPUT FROM VELOCITY CONTROL CIRCUIT +V S BCD TO DECIMAL DECODER 18 Pancake Resolvers >> Brush Type Motors >> CURRENT SENSE OUTPUT Brushless DC Motors Figure-14. Functional drive circuit for bi-directional control of a three phase brushless DC motor. Figure-15. Functional drive circuit for bi-directional control of a three phase brushless DC motor. Q7 Q8 Q9 Q10 Q11 Q12 +V SS Q1 Q4 Q2 Q5 Q3 Q6 0A Motor Windings www.axsys.com >
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