Linear Actuators & Solenoids#
Not every actuator spins. Solenoids produce linear push or pull motion over short strokes (typically 5–30 mm), relays switch high-power contacts using a magnetic coil, and linear actuators extend or retract over longer distances using an internal DC motor and leadscrew. All of these are inductive loads — they store energy in a magnetic field that must be safely dissipated when the drive signal is removed. The flyback voltage spike from a de-energized solenoid or relay coil can destroy an unprotected MOSFET in a single switching event.
From the firmware perspective, solenoids and relays are on/off devices (or proportionally driven with PWM dithering), while linear actuators behave like DC motors with limit switches. The drive circuitry principles — flyback protection, current limiting, thermal management — are shared with rotary motor drives, but the mechanical constraints (end-of-travel impacts, holding force vs pull-in force, duty cycle limits) add their own failure modes.
Pages#
- Solenoid Drive Circuits — Pull and push solenoids, flyback protection, drive transistor selection, and hold-current reduction techniques.
- Linear Actuator Control — DC motor-based linear actuators, limit switch integration, and position feedback options.
- Proportional Solenoid Control — PWM dithering for proportional force, valve control applications, and current regulation.
- Relay Drive Patterns — Relay coil driving, contact protection, solid-state relays, and contact bounce management.