Current Limit
It is the form of control that holds the current at a defined value instead of cutting it. When the current reaches the threshold the driver automatically reduces the duty ratio, so the motion continues, albeit at low speed. It is used to limit the starting surge and to prevent mechanical strain.
Its difference from cut-off protection is seen in its behaviour: overcurrent protection stops with a fault, whereas current limit turns the motor into a source producing constant torque. As the load gets heavier the speed falls but the current stays at the ceiling value.
Practical benefits:
- Start-up: the surge, which can rise to 5–8 times nominal, is held at the set value thanks to the limit; the voltage collapse on the battery and cable is reduced.
- Mechanical protection: an upper force limit is established; a door or shutter hitting an obstacle does not apply uncontrolled force.
- Thermal balance: the driver stays inside its own safe current window.
Running at the limit for a long time is still risky; because the motor draws full current although it is not turning, the winding heats up. That is why current limit is usually used together with a time limit, and the output is cut when the time expires. The current threshold settings on the KS250 and PT500 are likewise set with the same logic, above the real operating current and below the stall current.
Context where this term is used: DC Motor Driver Selection Guide