PWM (Pulse Width Modulation) is the defacto standard for controlling DC brushed motors with a micro controller. The output is constantly switching between 0 volts and max voltage at a rate of 20KHZ. The duty cycle of this switch varies from 0 to 100% to provide 0 to 100% voltage to the loco/track. The motor averages out this switching and just sees it as a DC voltage. In fact the motors work better with PWM at low speeds because the switching provides more torque and gets the motor started turning easier from a dead stop.
However, some train electronics are designed on the cheap, and they assume the input to their electronics will always be a nice pure DC signal (even though it never really is with track power due to many discontinuities while running over joints, through turnouts, etc.) and it causes problems. The motors will run fine, but the lights may act weird, and/or flicker. It won't cause any harm, it just doesn't look good. If you run into this problem, it can be fixed by using a PWM to Linear Converter, which will smooth out the PWM signal into a nice pure DC output. The Crest CRE-57091A has been tested with our products and works nicely. It is installed between the output of the No Frills Track Throttle, or the TrackSide R/C and the track.
However, some train electronics are designed on the cheap, and they assume the input to their electronics will always be a nice pure DC signal (even though it never really is with track power due to many discontinuities while running over joints, through turnouts, etc.) and it causes problems. The motors will run fine, but the lights may act weird, and/or flicker. It won't cause any harm, it just doesn't look good. If you run into this problem, it can be fixed by using a PWM to Linear Converter, which will smooth out the PWM signal into a nice pure DC output. The Crest CRE-57091A has been tested with our products and works nicely. It is installed between the output of the No Frills Track Throttle, or the TrackSide R/C and the track.
Note: The newer CRE-57091A has three input terminals, which is quite confusing. The center terminal is not used.