What is pulse width modulation pdf

The input to the differentiator is a PWM waveform. The differen-tiator generates positive and negative spikes corresponding to leading and trailing edges of the PWM waveform.

Diode Dl is used to bypass the positive spikes. The negative spikes are used to the trigger monostable multivibrator. The monostable multivibrator then generates the pulses of same width and amplitude with reference to trigger to give pulse position modulated waveform, as shown in figure 8.

One way to achieve this is illustrated in figure. As shown in figure 8. This reference pulse ,is generated by reference pulse generator of the receiver with the synchronization signal from the transmitter. The flip-flop circuit is reset or turned 'OFF' giving low output at the leading edge of the position modulated pulse. This repeats and we get PWM pulses at the output of the flip-flop. Disadvantages of PPM i Synchronization between transmitter and receiver is required.

These high frequencies of x t are affected. This type of effect is known as aperture effect. This is known as Reconstruction or Interpolation Filter. Open navigation menu. Close suggestions Search Search.

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If all three are on in equal amounts, the result will be white light of varying brightness. Blue equally mixed with green will get teal. The frequency of the square wave does need to be sufficiently high enough when controlling LEDs to get the proper dimming effect.

You can also use pulse width modulation to control the angle of a servo motor attached to something mechanical like a robot arm. Servos have a shaft that turns to specific position based on its control line. Our servo motors have a range of about degrees. With a 1. With a 1 ms pulse, the servo will be at the 0 degree position, and with a 2 ms pulse, the servo will be at degrees.

You can obtain the full range of motion by updating the servo with an value in between. PWM used to hold a servo motor at 90 degrees relative to its bracket. Pulse width modulation is used in a variety of applications particularly for control. You already know it can be used for the dimming of LEDs and controlling the angle of servo motors and now you can begin to explore other possible uses.

If you feel lost, feel free to check out the SparkFun Inventor's Kit which has examples using pulse width modulation. Rectification may serve in roles other than to generate direct current for use as a source of power.

As noted, detectors of radio signals serve as rectifiers. Rectifier Circuit Diagram In gas heating systems flame rectification is used to detect presence of flame. The simple process of rectification produces a type of DC characterized by pulsating voltages and currents although still unidirectional. It is a member of 78xx series of fixed linear voltage regulator ICs.

The voltage source in a circuit may have fluctuations and would not give the fixed voltage output. The voltage regulator IC maintains the output voltage at a constant value.

The xx in 78xx indicates the fixed output voltage it is designed to provide. Capacitors of suitable values can be connected at input and output pins depending upon the respective voltage levels. A voltage regulator IC is used to provide constant 5V dc supply to the microcontroller. Capacitors are used to remove the ripples. The following are the details about the PIC micro controller. The available features are summarized below Fig.

The Program Memory and Data Memory have separate buses so that concurrent access can occur. Accessing a location above the physically implemented address will cause a wraparound.

Table 4. Port B Functions Table 4. PORTC is multiplexed with several peripheral functions. Port C Functions Table 4. Each pin is individually configurable as an input or output. In this mode, the input buffers are TTL. Port D Functions Table 4. These pins have Schmitt Trigger input buffers. In this mode, the user must make certain that the TRISE bits are set, and that the pins are configured as digital inputs.

PORTE pins are multiplexed with analog inputs. The user must make sure to keep the pins configured as inputs when using them as analog inputs. Port E Functions Table 4. Figure 4. Up to bit resolution is available. This double-buffering is essential for glitch-free PWM operation. PWM is employed in a wide variety of applications, ranging from measurement and communications to power control and conversion.

Analog electronics: An analog signal has a continuously varying value, with infinite resolution in both time and magnitude. A nine-volt battery is an example of an analog device, in that its output voltage is not precisely 9V, changes over time, and can take any real-numbered value. Similarly, the amount of current drawn from a battery is not limited to a finite set of possible values. Analog voltages and currents can be used to control things directly, like the volume of a car radio.

In a simple analog radio, a knob is connected to a variable resistor. As you turn the knob, the resistance goes up or down. As that happens, the current flowing through the resistor increases or decreases.

This changes the amount of current driving the speakers, thus increasing or decreasing the volume. An analog circuit is one, like the radio, whose output is linearly proportional to its input. As intuitive and simple as analog control may seem, it is not always economically attractive or otherwise practical. For one thing, analog circuits tend to drift over time and can, therefore, be very difficult to tune. Precision analog circuits, which solve that problem, can be very large, heavy just think of older home stereo equipment , and expensive.

Analog circuits can also get very hot; the power dissipated is proportional to the voltage across the active elements multiplied by the current through them. Analog circuitry can also be sensitive to noise. Because of its infinite resolution, any perturbation or noise on an analog signal necessarily changes the current value.

Digital control : By controlling analog circuits digitally, system costs and power consumption can be drastically reduced. In a nutshell, PWM is a way of digitally encoding analog signal levels.

Through the use of high- resolution counters, the duty cycle of a square wave is modulated to encode a specific analog signal level. The PWM signal is still digital because, at any given instant 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 on-time is the time during which the DC supply is applied to the load, and the off-time is the periods during which that supply is switched off. Given a sufficient bandwidth, any analog value can be encoded with PWM. The duty cycle is the ratio of the on-time to the period; the modulating frequency is the inverse of the period. Communication and control: 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. Noise can only affect a digital signal if it is strong enough to change a logic-1 to a logic-0, or vice versa. Increased noise immunity is yet another benefit of choosing PWM over analog control, and is the principal reason PWM is sometimes used for communication.

Switching from an analog signal to PWM can increase the length of a communications channel dramatically. At the receiving end, a suitable RC resistor-capacitor or LC inductor-capacitor network can remove the modulating high frequency square wave and return the signal to analog form. PWM finds application in a variety of systems. As a concrete example, consider a PWM- controlled brake. To put it simply, a brake is a device that clamps down hard on something. In many brakes, the amount of clamping pressure or stopping power is controlled with an analog input signal.

The more voltage or current that's applied to the brake, the more pressure the brake will exert. The output of a PWM controller could be connected to a switch between the supply and the brake.

To produce more stopping power, the software need only increase the duty cycle of the PWM output. If a specific amount of braking pressure is desired, measurements would need to be taken to determine the mathematical relationship between duty cycle and pressure.

And the resulting formulae or lookup tables would be tweaked for operating temperature, surface wear, and so on. To set the pressure on the brake to, say, psi, the software would do a reverse lookup to determine the duty cycle that should produce that amount of force.

It would then set the PWM duty cycle to the new value and the brake would respond accordingly. If a sensor is available in the system, the duty cycle can be tweaked, under closed-loop control, until the desired pressure is precisely achieved.

PWM is economical, space saving, and noise immune. Pulse Width Modulation Techniques: 4. Single Pulse Width Modulation: In single pulse width modulation, only one pulse per half cycle is generated and the width of the pulse is varied to control the inverter output voltage. The gating signals are generated by comparing a rectangular reference signal with a triangular carrier signal. The figure 4. The frequency of the reference signal determines the fundamendal frequency of the output voltage.

Fig 4. Multiple Pulse Width modulation: The harmonics can be reduced by using several pulses in each half cycle of output voltage. The frequency of the reference signal sets the output frequency f0, and the carrier frequency fc determines the number of pulse per half cycle p. The modulation index controls the output voltage. This type of modulation signal is also known as uniform pulse width modulation UPWM.

Sinusoidal Pulse Width Modulation: Instead of maintaining the width of the pulses same as in the case of multiple pulse width modulation, the width of each pulses is varied in proportion to the amplitude of a sine wave. The gating signals are generated by comparing sinusoidal reference signal with a carrier triangular wave. The frequency of the reference signal fr determines the inverter output frequency f0 and its peak amplitude Ar controls the modulation index,M. The number of pulses per half cycle depends on the carrier frequency.

This sinusoidal pulse width modulation is commonly used in industrial applications. Sinusoidal Pulse Width Modulation 4. Harmonic Injected Modulation: The. Harmonic Injected Modulation is generated by injecting harmonics to the sine wave. This results in flat-topped waveform and reduces the amount of overmodulation.