PWM - Pulse Width Modulation

Pulse Width Modulation (PWM) technology is widely used for industrial applications such as measurement, motor control, power control and more. It offers a simple way for digital control logic to create an analog equivalence. By using Advantech¡¦s high-resolution counter cards, the duty cycle of a square wave can be modulated to encode specific analog signal levels so they can be used to control many electronic devices.

The following figures show the PWM signals of different duty cycles. Figure1 shows a PWM output at a 10% duty cycle; which means the signal is on for 10% of the period and off the other 90%. Figures 2 and 3 show PWM outputs at 50% and 90% duty cycles respectively. The PWM signals of different duty cycles stand for different analog signal values. For example, the power supply is 9V, so the PWM signal of 50 % results in equivalent 4.5V signal level.

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Figure1

Figure 2 shows a circuit that could be controlled by PWM signals. A bulb is powered by a 9V battery. If we close the switch connecting the battery and lamp for 50ms, the bulb would receive 9V during that interval. If we then opened the switch for the next 50ms, the bulb would receive 0V. If we repeat this cycle 10 times a second, the bulb will be lit as though it were connected to a 4.5V battery (50% of 9V). We say that the duty cycle is 50% and the modulating frequency is 10 Hz.

Figure2

The PWM signal is still digital because, in any given instance of time, the full DC supply is either fully on or fully off. The voltage or current source is supplied to the analog load by means of a repeating series of on and off pulses.

The popularity of PWM will continue to grow as its functionality becomes more popular in microcontrollers, and development tools make it easier to use. Having a good understanding of PWM will make it easier to incorporate in your designs.

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