This is implemented by connecting the motor high side and driving it with an N-channel MOSFET, which is driven again by a PWM signal. With a 0% duty cycle, the motor is off (no current flowing) with a duty cycle of 50% the motor runs at half power (half the current draw) and 100% represents full power at maximum current draw. In other words, the motor is powered for a small fraction of the time period – so over time the average power to the motor is low. The total power delivered is proportional to the duty cycle. Here, the motor is driven by a square wave with an adjustable duty cycle (the ratio of on time to the period of the signal). The solution to this problem is a method called PWM or pulse width modulation. The biggest drawback with this kind of setup is the efficiency – just like with any other load, the transistor dissipates all the unwanted power. If more current is needed, this circuit can be built discreetly with a few bipolar transistors. This can even be in the form of a variable linear regulator like the LM317 – the voltage across the motor can be varied to increase or decrease speed. It’s obvious that decreasing the voltage across the motor decreases the speed and a dead battery results in a slow motor but if the motor is powered from a rail common to more than one device, a proper driving circuit is needed. While this kind of setup is good for ‘static’ applications like a miniature windmill or fan, when it comes to a ‘dynamic’ application like robots, more precision is needed – in the form of variable speed and torque control.
And running it is as simple as connecting it to two cells – the motor fires up instantly and runs as long as the batteries are connected.
0 kommentar(er)
