How To Use Transistors For Motor Control?

Image source Electronics Lab

Motor and transistors are two common components in the world of electronics. While they are designed to serve different purposes, do you know that they can work together? In this case, a transistor can be used to control the behavior and operation of the motor. For this to happen, both the electronic devices have to be put in a single electric circuit. So, how do you use a transistor to achieve effective and reliable motor control? We have the answer.  Keep reading as we discuss all the ways and techniques in which transistors are used for motor control.

Overview of transistors

Transistors are common electronic components that are used for two main functions which are switching and amplification. It is quite interesting that both functions are deployed when using transistors to control motors even though the switching functionality seems to be the most deployed function.

When used as a switch, the transistor can change the state of the circuit hence influencing or affecting the rotation of the motor. As a digital switch, it is possible to use transistors to control motors that have high power and voltage requirements.

The second functionality of transistors in relation to motor control is amplification. This is relevant when the transistor is connected to a low signal source and is supposed to amplify the signal that will run the motor. Amplification is also important when you want to increase the speed or frequency at which the motor will rotate. For example, a transistor with a high pulse width modulation value will result in a fast rotation speed of the motor. The lower the PWM the slower the motor spin.

Each transistor comes with a defined current and voltage rating. So, when integrated into motor circuits, they determine the current that will flow through. In doing so,  the transistor will be serving as a voltage and current regulator.

While there are different types of transistors, Bipolar Junction Transistors (BJTs) are the most preferred transistor types for the motor control function. This type of transistor has three terminals which are the base, the collector, and the emitter. When you apply current on the base terminal, it will close the circuit between the collector and the emitter pins.

Beyond the type, configuration matters when using transistors for motor control. The two common configurations for BJTs are the NPN and PNP. The configurations will define how you connect the transistor to the circuit that runs the motor.

Overview of motor control

Now that you know the basics of transistors, let’s look at some of the mechanisms of electric motors and how they are related to transistors.

The working principle of electric motors is based on the induction process. An induction is generated when an electric charge passes through a coiled electric wire which results in the creation of a magnetic field. The more the current that flows through the coiled wire the stronger the magnetic field.

In the middle of this coiled magnetic field is a motor shaft, which is responsible for executing the rotary action of the motor. The magnetic force that has been created by the surrounding field will make this shaft rotate continuously.

Take note that electric motors still rotate even after being turned off. This is mainly because there is a small amount of current that is generated by the rotating motor. Electronic components such as transistors and diodes are used to direct this generated current away from the circuit so that it does not cause any damage.

Also, motors tend to draw the most current at the start-up. The consumption will remain constant when the motor is in the running state. When you want the motor to spin faster, the consumption will go up again. Once you turn the motor off, it will be running on a stall current.

Each induction motor comes with a voltage rating which is always defined as the peak operating voltage for the motor. All the components such as transistors and resistors should be designed to deliver peak voltage to the motor for the optimum efficiency levels.

How to connect the transistor to the motor control circuit?

For a transistor to be used for motor control, here, you first have to make the right connections in the circuit. An Arduino board will provide a perfect platform for making the connection. Other that the transistor, you will also need a resistor and a temporary switch button.

The button is positioned at the center of the breadboard and is connected to one board of the breadboard. You should also connect the pin of this terminal to a resistor and the other terminal of the switch to a 5-volt power source.

When it comes to the transistor, the base is connected to the Arduino pin that is from te voltage source. The collector terminal of the BJT is connected to the motor while the emitter is to the ground. The other terminal of the motor is connected to the positive terminal of the voltage source.

Check out the image below for reference

Image source ITP/IMA

Transistors as pulse width modulation in motors

The most common way in which transistors are used in induction motors is through pulse width modulation (PWM). Pulse width modulation is a common feature in both digital and analog electronics. When it comes to the operation of an induction motor, PWM determines the speed and rate at which the duty cycles vary or change.

So, where do transistors come in? Switching is one of the essential functions of a transistor. The fact that transistors have a fast-switching speed makes them perfect for the pulse modulation functionality. PMW is responsible for regulating the speed of an electric motor. It also allows you to change the speed of a motor without affecting other components of the circuit. This is possible thanks to the rapid switching behavior of the transistor.

In conclusion, transistors are vital electronic components in motor control circuits. They had a direct impact on how the motors run or operate. If you are building such a project, it will be smart to buy quality transistors from reputable suppliers in China.

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