With a H-bridge there is also a 'dead time' between switching of the top transistor off and switching the bottom transistor on. With very low PWM rates the motor gets a current ( = Torque) 'jolt' each time the PWM turns on which helps to overcome static friction.Īn then during the off part of the PWM cycle the motor will coast a bit.Ībove a PWM frequency of 10Hz to 50Hz these 'jolts' and 'coast' phases are usually not noticable because they are averaged (integrated) by the inertia of the motor. This averaged current is not enough to overcome static friction at low PWM duty cycles. The PWM voltage is averaged (integrated) by the inductance of the motor.

With a high PWM rate you almost have constant current through the motor. Second I've had better experiences with very low Frequencies. Ka7ehk wrote: You probably want the PWM frequency above 20KHz (to make it harder to hear).įirst the old designs of the L293 and L298 are probably not fit for such high PWM frequencies. What's the reason for this to happen and how can I make the motor to move at slower speeds if I can't use low values? I'm trying to make a PID controller to control the motor position and I need those small values. The power supply I used shows the current aswell and the motor needs around 0.4A (measured when the motor is directly connected to the power supply) to start rotating but when driving the motor through the h-bridge and giving it a PWM with a duty cycle below 45% the motor doesn't move and the power supply shows around 0.13A. I even changed the L293D for a L298N that has lower voltage drops (I fed it with 6V and the motor was receiving the 6V) and is capable of driving higher currents, but it also made no difference. I noticed that the L293D circuit drops some voltage, and instead of receiving 6V the motor was receiving a bit over 3V, so I fed the L293D with 9V instead of 6V and the motor was receiving around 5.8V, but it made no difference (beside moving faster).

I've tried all PWM frequencies that the microcontroller can create and the higher the frequency the higher the duty cycle has to be to make the motor rotate.īut if I use a power supply, directly connected to the motor, it works perfectly, for any voltage. For duty cycles between 40%-45% if I give it a push with my hand it rotates. I'm controlling a 6V DC motor using a microcontroller (Atmega328) that creates a PWM signal that is fed to a H-bridge (L293D), the problem is that the motor only moves when I set the PWM with a duty cycle of 45% or higher, if it has a lower duty cycle it doesn't move and makes a noise.

L298n motor driver not working