What does PWM mean

Pulse width modulation (PWM) is the abbreviation of English "Pulse width modulation", referred to as pulse width modulation.

It is a very effective technology to control analog circuits by using digital output of microprocessor, which is widely used in many fields such as measurement, communication, power control and transformation. A simulation control mode, according to the change of the corresponding load to modulate the transistor gate or base pole bias, to achieve the switching voltage regulator output transistor or transistor conduction time change, this way can make the output voltage of the power supply in the working conditions to maintain a constant.

Pulse width modulation (PWM) is a method of digitally encoding analog signal levels. Using the high resolution counter, the duty ratio of square wave is modulated to encode the level of a specific analog signal. The PWM signal is still digital, because at any given moment, the full amplitude of the DC power supply is either fully (on) or completely free (off). The voltage or current source is added to the simulated load by a repetitive pulse sequence with a pass (on) or a break (off). When the pass is the DC power is added to the load, when the break is the power is disconnected. As long as the bandwidth is sufficient, any analog value can be encoded using PWM.

Most of the load (whether inductive or capacitive) requires a modulation frequency higher than 10Hz, usually with a modulation frequency of 1kHz to 200kHz.

Many microcontrollers contain a PWM controller inside them. For example, the microchip company's pic16c67 contains two PWM controllers, each of which can choose the time and cycle to connect. The duty cycle is the ratio of the switching time to the period, and the modulation frequency is the reciprocal of the cycle. Before performing a PWM operation, this microprocessor requires that the following work be done in the software:

* Set the cycle of on-chip timer/counter with modulated square wave

* Set the time of the switch in the PWM control register

* Set the direction of the PWM output, this output is a general-purpose I/O pin

* Start Timer

* Enabling PWM Controller

One advantage of PWM is that the signal from the processor to the controlled system is in digital form, without the need for a numerical conversion. Keeping the signal in digital form minimizes the noise impact. Noise can affect digital signals only if it is strong enough to change logic 1 to logical 0 or to change logical 0 to logical 1 o'clock.

The enhancement of noise resistance is another advantage of PWM relative to analog control, and this is the main reason why PWM is used for communication at some times. Switching from analog to PWM can greatly prolong the communication distance. At the receiving end, the modulated high-frequency square wave is filtered through the appropriate RC or LC network, and the signal can be restored to analog form.

In short, the PWM is economical, space-saving, strong anti-noise performance, is a kind of useful engineers in many design applications of effective technology.