PWMdrift

PWMdrift is a term used to describe the deviation between the commanded duty cycle of a pulse-width modulation PWM signal and the actual average duty cycle observed at the load over time or under changing conditions. It can manifest as a slow drift in effective duty or as rapid fluctuations due to jitter. In practice, PWMdrift affects any system that relies on PWM for control, including motor drivers, DC-DC converters, and LED drivers.

Causes of PWMdrift include clock frequency instability in the PWM timer or peripherals, timer interrupt latency, resolution limits for high-frequency PWM, dead-time and switching delays in half-bridge configurations, and the nonideal response of the load or measurement chain. Temperature, supply voltage variation, aging of components, and PCB parasitics can also shift the effective duty cycle.

Measurement and modeling involve comparing commanded duty with measured average duty using an oscilloscope or high-resolution ADC, often across a range of load conditions. Models may treat drift as a function of time, temperature, supply, or duty; some approaches use state estimation methods to predict and compensate for drift.

Mitigation strategies include increasing PWM resolution or frequency, using hardware with a more stable clock, calibrating the PWM output as part of a feedback loop, implementing temperature compensation, and adding closed-loop control that adjusts the duty cycle based on measured output.

See also: pulse-width modulation, clock drift, jitter, closed-loop control, sensor calibration.