Voltage can be changed by raising the series resistance within the electrical circuit, which in turn lowers the current through the motor. PWM signal showing various duty cycles at a 250 Hz carrier frequency.ĭC motor speed and direction are dictated by the voltage applied - change or reverse the polarity of the voltage and the motor will respond in a similar fashion. If our PWM controller outputs a voltage of 12 volts DC, then a 50% duty cycle would provide the equivalent of 6 volts DC to power the load.įigure 2.

When controlling motors or heaters we use the duty cycle to dictate the power. If it is lowered to 50%, the signal will be on for half of the pulse and off for the other half. If the duty cycle is 100%, the signal will be on all the time. The duty cycle of a PWM signal is the relative amount of time the signal will be on and is expressed as a percentage. The key determining factor is the response rate of the load device. But for a solid-state device like a relay or LED, the frequency may need to be much higher - perhaps tens of thousands of hertz. For an electrical heater or motor, the frequency can be quite slow, perhaps in the tens to hundreds of Hz. The switching speed, or frequency, of the pulse depends on the load device that is using the signal. Understanding signals in AC and DC circuits is critical for proper operation of the devices. Two key parameters control the PWM signal - the frequency of the switching, and the relative duration of the on-time, called the ‘duty cycle’.įigure 1. This average voltage provides an equivalent lower power, while still maintaining full voltage for the on-state duration of the pulse. As the relative on-time of the signal increases or decreases, so does the average voltage of the signal. To provide variable control without sacrificing operating ability, a different method was needed.Ī PWM, or ‘pulse width modulation’ signal is used to reduce the electrical power supplied to an electrical device by switching the signal on and off at a high frequency. To change the parameters of the load, the voltage can be lowered, but this will often have negative effects, such as decreasing the torque of a motor, or lowering the voltage below the forward bias level of a transistor or LED series.

Load devices are designed to run efficiently and perform their respective tasks when provided with a certain voltage, consuming a particular amount of current.

How to increase pulse width