Proyecto PWM (Inglés)
- 1. Index Pag. • Objetives 3 IPN • • ESCOM • Theoretical introduction 3-6 • • Circuit 7 • • Circuit Explain 8 • Final Project • Simulations 9-10 • • Proyect Images 11-15 Modulation PWM • • Diagram Ishikawa 16 • • Datasheets 17-21 Analogical Electronic • • Chronogram 22 • • Conclusions 23 Teachers: • • Bibliography 23 Felipe Figueroa del Prado Raúl Santillán Luna Student: Martínez Vargas Jonathan Arturo Group: 2CV9 Delivery Date: 01/ 12/ 11
- 2. - Objetive Across this final project for the material of Analogical Electronics, we seek to apply several of the concepts learned in class as well as to use correctly the devices that were learned to use in this subject. As well as such to design the final project there seeks to use each of the previous knowledge of circuits for the functioning of the same one, and to generate a practical application for our design. This latter expression can be fairly simplified in many cases where ymin = 0 as . In this case to use the configuration of the Operational Amplifiers as comparators of Voltage to From this, it is obvious that the average value of the signal ( ) is directly dependent on the duty realize a modulation of Width of Pulse, it will be in use for controlling speed and intensity of some cycle D. electronic elements, since they it can be ventilators, motors or incandescent lamps. The simplest way to generate a PWM signal is the intersective method, which requires only - Theoretical introduction a sawtooth or a triangle waveform (easily generated using a simple oscillator) and a comparator. When the value of the reference signal (the red sine wave in figure 2) is more than the modulation Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a commonly used waveform (blue), the PWM signal (magenta) is in the high state, otherwise it is in the low state. technique for controlling power to inertial electrical devices, made practical by modern electronic power switches. The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is. The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switchings have to be done several times a minute in A simple method to generate the PWM pulse an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor train corresponding to a given signal is the intersective PWM: the signal (here the red drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies. sinewave) is compared with a sawtooth The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; waveform (blue). When the latter is less than the former, the PWM signal (magenta) is in a low duty cycle corresponds to low power, because the power is off for most of the time. Duty high state (1). Otherwise it is in the low state cycle is expressed in percent, 100% being fully on. (0). 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, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle. PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications channel. Pulse-width modulation uses a rectangular pulse wave whose pulse width is modulated resulting in the variation of theaverage value of the waveform. If we consider a pulse waveform f(t) with a low value ymin, a high value ymax and a duty cycle D, the average value of the waveform is given by: As f(t) is a pulse wave, its value is ymax for and ymin for . The above expression then becomes:
- 3. Applications (typically less than 100 nanoseconds), the power dissipation in the switches can be quite low compared to the power being delivered to the load. In telecommunications, the widths of the pulses correspond to specific data values encoded at one end and decoded at the other. Modern semiconductor switches such as MOSFETs or Insulated-gate bipolar transistors (IGBTs) are well suited components for high efficiency controllers. Frequency converters used to control AC Pulses of various lengths (the information itself) will be sent at regular intervals (the carrier motors may have efficiencies exceeding 98 %. Switching power supplies have lower efficiency due frequency of the modulation). to low output voltage levels (often even less than 2 V for microprocessors are needed) but still more than 70-80 % efficiency can be achieved. _ _ _ _ _ _ _ _ Variable-speed fan controllers for computers usually use PWM, as it is far more efficient when | | | | | | | | | | | | | | | | compared to a potentiometer or rheostat. (Neither of the latter is practical to operate Clock | | | | | | | | | | | | | | | | electronically; they would require a small drive motor.) __| |____| |____| |____| |____| |____| |____| |____| |____ Light dimmers for home use employ a specific type of PWM control. Home-use light dimmers _ __ ____ ____ _ typically include electronic circuitry which suppresses current flow during defined portions of each PWM Signal | | | | | | | | | | cycle of the AC line voltage. Adjusting the brightness of light emitted by a light source is then | | | | | | | | | | merely a matter of setting at what voltage (or phase) in the AC halfcycle the dimmer begins to _________| |____| |___| |________| |_| |___________ provide electrical current to the light source (e.g. by using an electronic switch such as a triac). In Data 0 1 2 4 0 4 1 0 this case the PWM duty cycle is the ratio of the conduction time to the duration of the half AC cycle defined by the frequency of the AC line voltage (50 Hz or 60 Hz depending on the country). The inclusion of a clock signal is not necessary, as the leading edge of the data signal can be used These rather simple types of dimmers can be effectively used with inert (or relatively slow as the clock if a small offset is added to the data value in order to avoid a data value with a zero reacting) light sources such as incandescent lamps, for example, for which the additional length pulse. modulation in supplied electrical energy which is caused by the dimmer causes only negligible additional fluctuations in the emitted light. Some other types of light sources such as light-emitting _ __ ___ _____ _ _____ __ _ diodes (LEDs), however, turn on and off extremely rapidly and would perceivably flicker if supplied | | | | | | | | | | | | | | | | with low frequency drive voltages. Perceivable flicker effects from such rapid response light PWM Signal | | | | | | | | | | | | | | | | sources can be reduced by increasing the PWM frequency. If the light fluctuations are sufficiently __| |____| |___| |__| |_| |____| |_| |___| rapid, the human visual system can no longer resolve them and the eye perceives the time |_____ average intensity without flicker. In electric cookers, continuously-variable power is applied to the heating elements such as the hob Data 0 1 2 4 0 4 1 0 or the grill using a device known as a Simmerstat. This consists of a thermal oscillator running at approximately two cycles per minute and the mechanism varies the duty cycle according to the knob setting. The thermal time constant of the heating elements is several minutes, so that the Power delivery temperature fluctuations are too small to matter in practice. Voltage Regulation PWM can be used to control the amount of power delivered to a load without incurring the losses that would result from linear power delivery by resistive means. Potential drawbacks to this PWM is also used in efficient voltage regulators. By switching voltage to the load with the technique are the pulsations defined by the duty cycle, switching frequency and properties of the appropriate duty cycle, the output will approximate a voltage at the desired level. The switching load. With a sufficiently high switching frequency and, when necessary, using additional noise is usually filtered with an inductor and a capacitor. passive electronic filters, the pulse train can be smoothed and average analog waveform One method measures the output voltage. When it is lower than the desired voltage, it turns on recovered. the switch. When the output voltage is above the desired voltage, it turns off the swit High frequency PWM power control systems are easily realisable with semiconductor switches. As explained above, almost no power is dissipated by the switch in either on or off state. However, during the transitions between on and off states, both voltage and current are non-zero and thus power is dissipated in the switches. By quickly changing the state between fully on and fully off
- 4. -Circuit -Explain To begin the diodes they will rectify the sign that goes out of our transformer that has diminished it to only 6V for phase, which later we will add in an alone rectified line, to be able to produce the positive of our operational amplifier. Later our voltage of reference will be the same of rectified entry, and will be compared with our another rectified phase. For which practically there will no be loss of voltage, with which we will be able to take her to our second operational operator, who with this sign will compare another sign, which will be regulated by the dimmer, to determine the level that will be the limit between lit and extinguished of our circuit. Being this also a divisor of voltage that as such establishes the voltage of reference that we need. And the Voltage of exit of our amplifier will come at the entry of the MOC to activate it, and to do the switcheo with the Triac, in order that it could activate the exits of our circuit, and this way change the sign of exit. But as the Triac he handles AC we must do a small bridge to our phase in order that the exit works like it must be.
- 5. -Simulations (View the potentiometer )
- 6. -Proyect Images In this part we can observe some images relating to the accomplishment of the printed plate, which he was carrying to iron the circuit in a phenolic plate and later to treat it with Ferric Chloride, to withdraw the copper that on in our plate.
- 7. Finally to stay of the following way: Removing the Tóner, and piercing the Pad's there will stay our plate ready to mount the components of our circuit, and to start welding.
- 9. - DATASHEET
- 11. -Chronogram November 2011 December 2011 7 9 18 20-30 1 2 Design of the Circuit It delivers of Offer Offer Accepted Accomplishment of the Project (Physicist and Writing) To raise File Delivery Project End
- 12. -Conclusions With this project we can check by means of the exit of signs, the seen previously in Comparators laboratory practice of Voltage. Having a voltage d reference in each of the terminuses of our AO we can stabilize and control certain level of activation for the following circuit, in order that it is a limit of "on" and "off". Being the ignition when this level is exceeded, and the subdued one when our voltage tends to come below our proposed limit. We can observe also since it is that the exit of our comparator of voltage, handled as PWM's sign also is in exit a square sign, which changes his extent. Depending on the value that takes our dimmer, which in this case together with the arrangement of resistances acts as divisor of voltage, to establish the parameters necessary for the last AO. Which gives us an idea of how this application can be used to determine the speed of draft of some engine, the intensity of some lamp or some another application that is compatible with the exit of our circuit PWM. That enclosed it is possible to say that these applications are very used in the projects, already is without the modulation, the comparison of voltages, to activate another circuit is very used in the applications of analogical circuits, or even in some applications of Digital electronics. -Bibliography "Electronic Devices and Circuit Theory," Prentice Hall, Boylestad, R and Nashelsky, L. 9th ed. 2005