Overview
This post explains the DC motor PWM speed controller shown in your Proteus schematic (NE555 driving an N-channel MOSFET). It’s ideal for hobby projects, robotics, small pumps, fans, and educational demos. You’ll learn what it can control, how it works, and best practices for simulation and PCB design.
What this circuit CAN DO (Practical Capabilities)
- Smooth Speed Control: Adjust motor speed from ~10% to ~100% duty cycle using a potentiometer.
- Torque Preservation: PWM control ensures the motor keeps its torque even at lower speeds.
- Protection: Includes a flyback diode to protect the MOSFET from motor back-emf.
- Proteus Ready: Easy to simulate and visualize waveforms at the NE555 output and MOSFET drain.
How it Works — Simple, Step-by-Step
- NE555 as PWM Generator: The 555 timer produces a square-wave. Diodes and a pot allow the wiper to change the duty cycle while keeping the frequency constant.
- Driving the MOSFET: The 555 output connects through a 100Ω gate resistor to the MOSFET (IRFZ44N), acting as a low-side switch.
- Motor Connection: The motor is connected between +12V and the MOSFET drain.
- Decoupling: Electrolytic capacitors near supply pins prevent 555 mis-triggering.
Components & Proteus Selection
- IC: NE555 (DIP-8)
- MOSFET: IRFZ44N or IRLZ44N (Logic Level)
- Diode: 1N5819 (Schottky) or 1N4007
- Potentiometer: 100k Linear
- Resistors/Caps: 1k, 10k, 100Ω, 0.01µF, 0.1µF, 1µF, 100µF