What is PWM DC motor speed control? (2023)

What is PWM DC motor control?

Pulse-width modulation (PWM) or duty-cycle variation methods are commonly used in speed control of DC motors. The duty cycle is defined as the percentage of digital 'high' to digital 'low' plus digital 'high' pulse-width during a PWM period. Fig. 1 shows the 5V pulses with 0% through 50% duty cycle.

If we switch the power on and off quickly enough, the motor will run at some speed part way between zero and full speed. This is exactly what a p.w.m. controller does: it switches the motor on in a series of pulses. To control the motor speed it varies (modulates) the width of the pulses – hence Pulse Width Modulation.

If such a signal is fed to a DC motor, we can change the speed of the motor by changing the duty cycle of the PWM signal. The change in pulse width is created by increasing the on-time (HIGH value) of the pulse while reducing the off-time (LOW value) by the same amount so that the frequency of the signal is constant.

Pulse width modulation turns a digital signal into an analog signal by changing the timing of how long it stays on and off. The term “duty cycle” is used to describe the percentage or ratio of how long it stays on compared to when it turns off.

Using PWM allows precise current control in the windings. Hence, the output torque, which is linearly proportional to the average winding current, can be correctly controlled in coreless motors.

The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on and power is being transferred to the load, there is almost no voltage drop across the switch.

A PWM waveform can, however, create issues within a motor. For example, it can cause a motor winding to experience voltage spikes that are well above the rated voltage of both the motor and standard motor winding limits.

As its name suggests, pulse width modulation speed control works by driving the motor with a series of “ON-OFF” pulses and varying the duty cycle, the fraction of time that the output voltage is “ON” compared to when it is “OFF”, of the pulses while keeping the frequency constant.

Pulse width modulation or PWM is a commonly used control technique that generates analog signals from digital devices such as microcontrollers. In PWM technique, the signal's energy is distributed through a series of pulses rather than a continuously varying (analog) signal.

Why use PWM instead of analog?

One of the advantages of PWM is that the signal remains digital all the way from the processor to the controlled system; no digital-to-analog conversion is necessary. By keeping the signal digital, noise effects are minimized.

PWM (Pulse Width Modulation) One method that is often used for DC motor control using a microcontroller is Pulse Width Modulation (PWM) method. The speed of the electric motor depends on the modulator voltage. The greater the voltage, the faster the rotation of an electric motor.

PWM has many advantages and is the most widely used solution for brushless DC drivers. Setting an adequate PWM voltage and using a high PWM frequency will help to reduce the ripple and can avoid the use of additional inductances.

Power Consumption

Due to the way PWM fans function, they're generally more efficient than DC fans and use less power. Consider the duty cycles of PWM fans. When a fan is on a 40% duty cycle, it's only using electrical power 40% of the time. In comparison, the DC fans, if anything, will use a slightly lower voltage.

PWM is used in many applications, ranging from communications to power control and conversion. For example, the PWM is commonly used to control the speed of electric motors, the brightness of lights, in ultrasonic cleaning applications, and many more.

A higher frequency will cause a shorter cycle time of the PWM; hence the current will have less time to rise. PWM frequencies not less than 50 kHz for brushless dc motors are recommended. PWM frequencies of 80 kHz or more would be even more appropriate for motors with a very small electrical time constant.

Thus the PWM is NOT affecting the torque (and the current) but only the speed (and the voltage).

If you have a 3-pin fan connector, pick DC mode. On the other hand, if you have a 4-pin fan connector, select PWM mode. If your motherboard fan header only has 3 pins, pick DC regardless of whether you have a 4-pin PWM or 3-pin DC fan.

Due to the way PWM fans function, they're generally more efficient than DC fans and use less power. Consider the duty cycles of PWM fans. When a fan is on a 40% duty cycle, it's only using electrical power 40% of the time. In comparison, the DC fans, if anything, will use a slightly lower voltage.

What is better PWM or DC?

Stroboscopic effect evident in fast moving environments when the driver frequency is low. Electromagnetic Interference (EMI) issues due to rise and fall of the current in PWM dimming.

Pulse Width Modulation (PWM), also known as pulse-duration modulation (PDM), is a technique for reducing the average power in an Alternating Current (AC) signal. PWM meaning is effectively chopping off parts of the waveform to reduce the average voltage without affecting the base frequency of the signal.