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Ac dc converter

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theory of AC-DC converter and it's usage.

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Ac dc converter

  1. 1. • Introduction • Types of converter • How to work converter? • Application • Future of AC-DC converter
  2. 2. Энэ удаагийн хичээлээр Бидний өдөр тутмын амьдралд хэрэглэгддэг AC-DC хувиргуурын талаар авч үзнэ. Оролтын хувьсах хүчдлийн түвшинг гаралтандаа тогтмол болгон хувиргадаг төхөөрөмжийг ерөнхийдөө AC-DC Хувиргуур гэж ойлгож болно. In this topic we will learn about which is the used in our daily life’s Alternating Current to Direct Current converter. Generally, We can understand Input’s Alternating current to output’s direct current converts by AC-DC converter easily. AC-DC converters are such common devices that no one pays much attention to them unless they go missing and you can’t get the DC power that you need. It’s u
  3. 3. •Half wave •Full wave •Full wave bridge rectifier •Three-phase full-wave rectifier
  4. 4. For most power applications, half-wave rectification is insufficient for the task. The harmonic content of the rectifier’s output waveform is very large and consequently difficult to filter. Furthermore, the AC power source only supplies power to the load one half every full cycle, meaning that half of its capacity is unused. Half-wave rectification is, however, a very simple way to reduce power to resistive load.
  5. 5. Some two-position lamp dimmer switches apply full AC power to the lamp filament for “full” brightness (fig.A) and then half-wave rectify it for a lesser light (fig.B) output. In “DIM” switch position, the incandescent lamp receives approximately one-half the power it would normally receive operating on full-wave AC. Because the half- wave rectified power pulses far more rapidly than the filament has time to heat up and cool down , the lamp does not blink. Fig. A Fig. B
  6. 6. • A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to pulsating DC (direct current), and yields a higher average output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed. Single semiconductor diodes, double diodes with common cathode or common anode, and four-diode bridges, are manufactured as single components.
  7. 7. The full wave rectifier circuit consists of two power diodes connected to a single load resistance (RL) with each diode taking it in turn to supply current to the load. When point A of the transformer is positive with respect to point C, diode D1 conducts in the forward direction as indicated by the arrows. When point B is positive (in the negative half of the cycle) with respect to point C, diode D2 conducts in the forward direction and the current flowing through resistor R is in the same direction for both half-cycles. As the output voltage across the resistor R is the phasor sum of the two waveforms combined, this type of full wave rectifier circuit is also known as a “bi-phase” circuit. As the spaces between each half-wave developed by each diode is now being filled in by the other diode the average DC output voltage across the load resistor is now double that of the single half-wave rectifier circuit and is about 0.637Vmax of the peak voltage, assuming no losses.
  8. 8. Where: VMAX is the maximum peak value in one half of the secondary winding and VRMS is the RMS (root-main- square) value.
  9. 9. • Another type of circuit that produces the same output waveform as the full wave rectifier circuit above, is that of the Full Wave Bridge Rectifier. This type of single phase rectifier uses four individual rectifying diodes connected in a closed loop “bridge” configuration to produce the desired output. The main advantage of this bridge circuit is that it does not require a special centre tapped transformer, thereby reducing its size and cost. The single secondary winding is connected to one side of the diode bridge network and the load to the other side as shown below.
  10. 10. THREE PHASE AC-DC CONVERTER • Single-phase rectifiers are commonly used for power supplies for domestic equipment. However, for most industrial and high-power applications, three-phase rectifier circuits are the norm. As with single-phase rectifiers, three- phase rectifiers can take the form of a half-wave circuit, a full-wave circuit using a center-tapped transformer, or a full-wave bridge circuit. • Thyristors are commonly used in place of diodes to create a circuit that can regulate the output voltage. Many devices that provide direct current actually generate three-phase AC. For example, an automobile alternator contains six diodes, which function as a full-wave rectifier for battery
  11. 11. • For a three-phase full-wave diode rectifier, the ideal, no-load average output voltage is: • If thyristors are used in place of diodes, the output voltage is reduced by a factor cos(α): • Where: • Vpeak, the peak value of the phase (line to neutral) input voltages, • α, firing angle of the thyristor (0 if diodes are used to perform rectification)
  12. 12. Here is working of converter cycle.
  13. 13. The positive half-cycle During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but diodes D1 and D2 switch “OFF” as they are now reverse biased. The current flowing through the load is the same direction as before.
  14. 14. The Negative Half-cycle • As the current flowing through the load is unidirectional, so the voltage developed across the load is also unidirectional the same as for the previous two diode full- wave rectifier, therefore the average DC voltage across the load is 0.637Vmax
  15. 15. • However in reality, during each half cycle the current flows through two diodes instead of just one so the amplitude of the output voltage is two voltage drops ( 2 x 0.7 = 1.4V ) less than the input VMAX amplitude. The ripple frequency is now twice the supply frequency (e.g. 100Hz for a 50Hz supply or 120Hz for a 60Hz supply.)
  16. 16. The smoothing capacitor The smoothing capacitor converts the full- wave rippled output of the rectifier into a smooth DC output voltage. Generally for DC power supply circuits the smoothing capacitor is an Aluminium Electrolytic type that has a capacitance value of 100uF or more with repeated DC voltage pulses from the rectifier charging up the capacitor to peak voltage. However, their are two important parameters to consider when choosing a suitable smoothing capacitor and these are its Working Voltage, which must be higher than the no-load output value of the rectifier and its Capacitance Value, which determines the amount of ripple that will appear superimposed on top of the DC
  17. 17. Bridge Rectifier Ripple Voltage: Where: I is the DC load current in amps, ƒ is the frequency of the ripple or twice the input frequency in Hertz, and C is the capacitance in Farads. Another more practical and cheaper alternative is to use an off the shelf 3-terminal voltage regulator IC, such as a LM78xx (where “xx” stands for the output voltage rating) for a positive output voltage or its inverse equivalent the LM79xx for a negative output voltage which can reduce the ripple by more than 70dB (Datasheet) while delivering a constant output current of over 1 amp. In the next tutorial about diodes, we will look at the Zener Diode which takes advantage of its reverse breakdown voltage characteristic to produce a constant and fixed output voltage across itself.
  18. 18. • if we see deeply, We will find AC-DC converters around us. • Used in our communication technology, automated factory,
  19. 19. WEB SOURCES: • www.allaboutcircuits.com • https://en.Wikipedia.org • http://www.electronics-tutorials.ws/diode/diode_6.html

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