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 best practices for simulation and PCB and ready-to-use
What this circuit CAN DO (practical capabilities)
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Control motor speed smoothly from ~10% to ~100% duty cycle using a potentiometer — good for 12V DC motors (brushed)
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Provide PWM control with adjustable duty cycle so motor torque is conserved while average voltage changes
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Protect the circuit from motor back-emf with a flyback diode and optional snubber
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Be simulated in Proteus to visualize PWM at the NE555 output and voltage pulses at the MOSFET drain
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Be converted to a manufacturable PCB in Proteus ARES with proper footprints and wide power traces
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Be adapted: swap MOSFET for a logic-level device (IRLZ44N) for lower gate-threshold drives from 12V NE555 output, or move to higher voltages with appropriate parts
How it works — simple, step-by-step
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NE555 configured as PWM generator: The 555 produces a square-wave output. By using diodes and a potentiometer around the threshold/discharge nodes you get independent charge/discharge paths that let the wiper change the duty cycle while keeping frequency roughly constant
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Output drives MOSFET gate: The 555 output connects (through a gate resistor ~100Ω) to the MOSFET gate (IRFZ44N) — MOSFET acts as a low-side switch
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Motor connected to +12V and MOSFET drain: When MOSFET is ON, current flows from +12V → motor → MOSFET → GND. The average applied voltage (and so speed) depends on duty cycle
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Flyback diode across motor: Diode (1N5819 or 1N400x) clamps inductive spikes when MOSFET switches OFF. Optional RC snubber across motor reduces EMI
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Decoupling: 0.1µF and electrolytic caps near supply pins stabilize the supply and prevent 555 mis-triggering
Components & Proteus notes (what to pick in Proteus)
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IC: NE555 (DIP-8) — use the library “TIMER” / NE555
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MOSFET: IRFZ44N (TO-220). Note: IRFZ44N is not ideal for low-Vg logic-level drive; consider IRLZ44N if you want guaranteed low Rds(on) at gate voltages driven from NE555 (≈12V gate is okay, but IRLZ/logic-level is safer).
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Diode: 1N5819 (Schottky) or 1N4007 for flyback
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Potentiometer: 100k linear for duty control (can drop to 10k for faster response)
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Resistors / Caps 1k 10k 100Ω gate resistor 0.01µF 0.1µF 1µF timing cap 100µF supply cap
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Power 12V DC supply motor (rated near 12V)
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Proteus tips: attach correct PCB packages (DIP-8 for 555 TO-220 for MOSFET) Use probes/oscilloscope to capture Pin 3 (555 output) and MOSFET drain waveforms
Simulation checklist (Proteus)
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Turn on current flow animation (System → Set Animation Options → Show Current Flow)
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Place scope probes: Channel A → Pin 3 (PWM), Channel B → MOSFET drain
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Watch for switching spikes — add flyback diode or RC snubber if needed
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Sweep the potentiometer and record duty vs RPM behavior
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If MOSFET heats up in simulation, switch to a logic-level MOSFET or add heatsink in design
PCB & Real-build tips (manufacturable & reliable)
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Footprints: ensure MOSFET footprint has thermal pad and mounting hole if needed Verify capacitor lead pitch and connector footprints
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Trace width: motor +12V and ground traces must be wide for >2A use 1mm+ or add multiple pours/traces. Use a ground plane where possible
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Placement: MOSFET close to motor output trace decoupling caps close to 555 Vcc and to motor supply
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Thermal use a heatsink and thermal vias for MOSFET if motor draws high current
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EMI place 0.1µF across motor terminals and add ferrite bead on motor positive lead for noise suppression
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Test points add TP for gate, drain Vcc — helps debugging
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Gerber export in Proteus ARES run DRC then Output → Generate Gerber & Drill files. Verify with a Gerber viewer before sending to fab
Common improvements & variants
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Use logic-level MOSFET (IRL-series) for lower conduction loss
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Add current sensing (shunt + op-amp) for overload protection / closed-loop speed control
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Replace NE555 with microcontroller (Arduino) for advanced features: soft-start, braking, ramp-up profiles, reverse, or speed feedback via tachometer
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For quieter operation: change PWM frequency (higher frequency reduces audible noise but increases switching losses)
Real-world use cases / Applications
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Hobby robotics speed control
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Small conveyor belts, pumps, axial fans
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Lab benches and educational demos (showing PWM principle)
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DIY power tools (low-power) and prototyping motor driver stages
