Design-1
The design below has a minimum of 50% duty cycle and maximum of 100% duty cycle. It's capable of making the attached device performing at its peak (100% duty cycle, but it's unable to turn off the device completely (the device will still operate at 50% of its peak performance even when the potentiometer is turned all the way to the end).
Design-2
The design below can do 0 ~ 100% duty cycle.
For a chip that was designed back in 1970 ~ 1971 (I was around 1-year old at that time), this is truly an amazing chip. I salute you Hans R. Camenzind.
Put the circuit to work
Below are the videos showing the waveform and the running of the motor. One of the motor has 0.1uF capacitor across the positive and the negative terminal of the motor, and the other one doesn't.
DC 12V Brush Gear Motor PWM Speed Control - w. 0.1uF Cap.
DC 12V Brush Gear Motor PWM Speed Control - w/o 0.1uF Cap.
Note,
When the above design is used to drive motor via MOSFET, it's better to have the PWM frequency in the range of 10KHz (C TRI = 1nF), than 1KHz (C TRI = 10nF). See below scope screen shot for the difference.
The 1KHz operating range is within human audible frequency range. The noise may be annoy to some people.
References
LEDs, 555s, PWM, Flashers, and Light Chasers Index <-- Very good. Must read!!
http://forum.allaboutcircuits.com/blog/leds-555s-pwm-flashers-and-light-chasers-index.378/
Full range PWM (555)
http://forum.allaboutcircuits.com/threads/full-range-pwm-555.31324/
**555 on 24v Circuit**
http://www.555-timer-circuits.com/555-on-24v.html
**LM317 / LM338 Voltage Calculator** <- Very Useful!!
http://www.reuk.co.uk/LM317-Voltage-Calculator.htm
Simplest Method to Make a Motor Turn Off, Turn On, Go Forwards, and Go Backwards
http://www.robotroom.com/DPDT-Bidirectional-Motor-Switch.html
H Bridge Motor Speed Controller Tutorial
https://www.youtube.com/watch?v=iYafyPZ15g8
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