7
7: Motor Driver equivalent circuitry – a multiple transis-
tor switch connects the motor to the power supply in one
direction or the other or not at all.
Modern decoder designs have the pulse rate in the 15,000
to 30,000 times per second range. Why? This puts the drive
pulses outside the range of human hearing. Even though the
motor will “sing” just a bit, it will be beyond our ability to hear
it. Manufactures call this feature things like “silent drive” or
“supersonic drive”.
BEMF (motor control)
Most decoders today offer BEMF motor control. As I discussed
in my December 2012 column on Basic Electronics
, the motor will generate a reverse voltage
(Back EMF) that is directly proportional to its speed. A detector
across the orange and gray wires can sense this voltage dur-
ing the time that the motor driver is switched off. Providing
