During load testing, I noticed different behavior depending on the type of load connected to the PWM output.
When using a coil and operating the output in current-control mode, the requested current is regulated correctly.
However, when an incandescent light bulb is connected, the measured current is approximately 30% higher than the requested value, particularly at setpoints above 1 A. The measurement was taken using a True RMS current clamp.
The current also appears to fluctuate significantly instead of remaining stable.
What could cause this behavior when using an incandescent bulb as the load?
The PWM output can operate in different control modes: duty-cycle control, current control, and voltage control.
This means the same RX command interface can be used while selecting the output-control method that is most suitable for the connected load.
For inductive loads such as coils, current-control mode is generally appropriate because the load characteristics allow the current regulation loop to operate as intended.
An incandescent lamp, however, behaves as a strongly resistive and nonlinear load. Its filament resistance changes significantly with temperature, especially during heating and cooling within the PWM cycle. This can cause current-control mode to behave differently and may result in current oscillation or measurements that differ from the requested value.
For resistive loads such as incandescent lamps, using duty-cycle mode or voltage-control mode is therefore recommended instead of current-control mode.