Here is a simple circuit with current-limiting to protect an N-Channel MOSFET. The comparator is set to limit current to 30 amps in order to protect the MOSFET that is rated 40 amps.
During normal operation a PWM signal is driving the Gate of the MOSFET, which in turn provides a path to GND for the electric motor. The comparator has an open-collector output and the voltage divider on the non-inverting input of the comparator is set to 3V. The comparator is not actually measuring current but measuring voltage across the 0.1 ohm resistor to provide current-limiting. The 0.1 ohm resistor is acting like a current to voltage convertor. Here's how it works.
When the electric motor is stalled or starting from a standstill, there is a tremendous amount of current that the motor sinks. The purpose of the current-limit is to protect the MOSFET and not the motor. Let's say the motor ramps up and starts to sink 30 amps. 30 amps through the 0.1 ohm resistor will give us, using ohms law...
V = IR
= (30A) x (0.1 ohm)
= 3V
Since the reference voltage on the non-inverting side of the comparator is set to 3V and the voltage measured across the 0.1 ohm is 3V, the output of the comparator will start to pull the Gate of the MOSFET to GND limiting the current.
More to come...
During normal operation a PWM signal is driving the Gate of the MOSFET, which in turn provides a path to GND for the electric motor. The comparator has an open-collector output and the voltage divider on the non-inverting input of the comparator is set to 3V. The comparator is not actually measuring current but measuring voltage across the 0.1 ohm resistor to provide current-limiting. The 0.1 ohm resistor is acting like a current to voltage convertor. Here's how it works.
When the electric motor is stalled or starting from a standstill, there is a tremendous amount of current that the motor sinks. The purpose of the current-limit is to protect the MOSFET and not the motor. Let's say the motor ramps up and starts to sink 30 amps. 30 amps through the 0.1 ohm resistor will give us, using ohms law...
V = IR = (30A) x (0.1 ohm) = 3VSince the reference voltage on the non-inverting side of the comparator is set to 3V and the voltage measured across the 0.1 ohm is 3V, the output of the comparator will start to pull the Gate of the MOSFET to GND limiting the current.