The LEDs must have different forward voltage drop specifications, as we have for red, orange, yellow, and green LEDs. You can add LEDs parallel to the motor for getting a quick speed indication. When it comes to controlling motor speed uniformly and efficiently, a PWM based controller becomes the ideal option, here we will learn more, regarding a simple circuit to implement this operation. This happens because the difference between the gate and the source pin of the mosfet must be always around 5V, in order to enable the mosfet to conduct optimally. Here we can clearly see that the mosfet source pin seems to be "following" the gate and hence the name source follower.
12 volt forward and reverse motor full#
When the gate voltage is around 7V, the source pin will supply the minimum 2V to the motor causing a very slow spin on the motor, and 7V will be available across the source pin when the pot adjustment generates the full 12V across the gate of the mosfet. It implies that the source will be always 4 or 5V lagging behind the gate voltage and vary up/down with this difference, presenting a varying voltage between 2V and 7V across the motor. In the above DC motor controller design, the pot adjustment creates a varying potential difference across the gate of the mosfet, and the source pin of the mosfet simply follows the value of this potential difference and adjusts the voltage across the motor accordingly.
Design#1: Mosfet based DC Motor Speed ControllerĪ very cool and easy DC motor speed controller circuit could be build using a just a single mosfet, a resistor, and a pot, as shown below:Īs can be seen the mosfet is rigged as a source follower or a common drain mode, to learn more about this configuration you may refer to this post, which discusses a BJT version, nevertheless the working principle remains the same. 3 easy to build speed controller circuits for DC motors are presented here, one using MOSFET IRF540, second using IC 555 and the third concept with IC 556 featuring torque processing.