Yrd. Doç. Dr. Aytaç Gören

Transcription

1 H2 - AC to DC Yrd. Doç. Dr. Aytaç Gören

2 ELK Contents W01 Basic Concepts in Electronics W02 AC to DC Conversion W03 Analysis of DC Circuits W04 Transistors and Applications (H-Bridge) W05 Op Amps and Applications W06 Sensors and Measurement (1/2) W07 Sensors and Measurement (2/2) W08 Midterm W09 Basic Concepts in Digital Electronics (Boolean Algebra, Decimal to binary, gates) W10 Digital Logic Circuits (Gates and Flip Flops) W11 PLC s W12 Microprocessors W13 Data Acquisition, D/A and A/D Converters. 2

3 ELK 2018 W01 Contents 1. AC Form and values of grid 2. Potentiometer 3. Transformers 4. Semi Conductors 5. Diodes 6. Conversion to DC 1. Half Wave Rectifier 2. Half Wave Rectifier with Smoothing Capacitor 3. Using full wave rectifier 4. Using diode bridge rectifier Voltage Regulator IC 8. Switch Mode Power Supply Selection 3

4 Why conversion? Electricity is transferred from power plants to houses or business as alternate current because of decreasing losses during transfer. On the other hand, semi conductors use direct current. Thus, it is needed to be changed to direct current. A rectifier is a circuit which converts the Alternating Current (AC) input power into a Direct Current (DC) output power. Yrd. Doç. Dr. Aytaç Gören

5 Yrd. Doç. Dr. Aytaç Gören Potentiometer

6 Potentiometer Yrd. Doç. Dr. Aytaç Gören

7 Transformers Ref: 7 Yrd. Doç. Dr. Aytaç Gören

8 Transformers K trafo N N S P V V S P I I P S 8 Ref: Yrd. Doç. Dr. Aytaç Gören

9 Semi Conductors Semiconductors materials such as silicon (Si), germanium (Ge) and gallium arsenide (GaAs), have electrical properties somewhere in the middle, between those of a "conductor" and an "insulator". They are not good conductors nor good insulators (hence their name "semi"-conductors). They have very few "fee electrons" because their atoms are closely grouped. That is due to the strength of the molecular bounds However, their ability to conduct electricity can be greatly improved by adding certain "impurities" to this crystalline structure thereby, producing more free electrons than holes 9

10 Semi Conductors The most commonly used semiconductor basics material by far is silicon. Its atomic number is 14 Silicon has four valence electrons in its outermost shell Semiconductors- Silicon The structure of the bond between the two silicon atoms is such that each atom shares one electron with its neighbour This bound is very stable and called as co valent bound crystals of pure silicon (or germanium) are therefore good insulators. 10

11 Semi Conductors Semiconductor N-type In order for our silicon crystal to conduct electricity, we need to introduce an impurity atom such as Arsenic, Antimony or Phosphorus These atoms have five outer electrons in their outermost orbital to share with neighbouring atoms. This allows four out of the five orbital electrons to bond with its neighbouring silicon atoms leaving one "free electron" to become mobile when an electrical voltage is applied. The resulting semiconductor material has extra electrons, each with a negative charge, and is therefore referred to as an "N-type" material 11

12 Semi Conductors Another way to make silicon crystal conduct electricity is to add impurity atoms such as Aluminium, Boron or Indium, which have only three valence electrons Semiconductor P-Type Therefore, a complete connection is not possible, giving the semiconductor material an abundance of positively charged carriers known as "holes" in the structure of the crystal where electrons are effectively missing. The doping of such atoms causes conduction to consist mainly of positive charge carriers resulting in a "Ptype" material with the positive holes 12

13 Semi Conductors Semiconductor PN Junction These semiconductor N and P-type materials do very little on their own as they are electrically neutral, but when we join (or fuse) them together these two materials behave in a very different way producing what is generally known as a PN Junction. When the N and P-type semiconductor materials are first joined together a diffuusion phenomena occurs. The free electrons from the N-type impurity atoms begin to migrate across this newly formed junction to fill up the holes in the P-type material 13

14 Semi Conductors This process continues back and forth until the number of electrons which have crossed the junction have a large enough electrical charge to repel or prevent any more carriers from crossing the junction. Eventually a state of equilibrium (electrically neutral situation) will occur producing a "potential barrier" zone around the area of the junction This area around the junction is now called the Depletion Layer.(gerilim seti) This layer produces a potential difference vallue of for silicon about volts and for germanium about volts. This potential barrier will always exist even if the device is not connected to any external power source. Semiconductor PN Junction 14

15 Semi Conductors However, if we were to make electrical connections at the ends of both the N-type and the P-type materials and then connect them to a battery source.this additional energy source overcomes the barrier resulting in free charges being able to cross the depletion region from one side to the other. The behavior of the PN junction with regards to the potential barrier width produces an asymmetrical conducting two terminal device, better known as the Junction Diode. A diode is one of the simplest semiconductor devices, which has the characteristic of passing current in one direction only However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential I-V relationship PN Junction Diode 15

16 Semi Conductors There are two operating regions for a diode: Forward biased and Reverse biased. Operation of a Diode When a diode is connected in a Reverse Bias condition, a positive voltage is applied to the N-type material and a negative voltage is applied to the P-type material. When a diode is connected in a Forward Bias condition, a negative voltage is applied to the N-type material and a positive voltage is applied to the P-type material. 16

17 Diodes 17

18 Diodes (open door/closed door) 18

19 Diodes (more ) Leds are also diodes which emit light. 19

20 Ref: 20 Yrd. Doç. Dr. Aytaç Gören Diodes The power semiconductor diode, known simply as the Power Diode, has a much larger PN junction area compared to its smaller signal diode cousin, resulting in a high forward current capability of up to several hundred amps (KA) and a reverse blocking voltage of up to several thousand volts (KV). Since the power diode has a large PN junction, it is not suitable for high frequency applications above 1MHz, but special and expensive high frequency, high current diodes are available. For high frequency rectifier applications Schottky Diodes are generally used because of their short reverse recovery time and low voltage drop in their forward bias condition.

21 Diodes If an alternating voltage is applied across a power diode, during the positive half cycle the diode will conduct passing current and during the negative half cycle the diode will not conduct blocking the flow of current. Then conduction through the power diode only occurs during the positive half cycle and is therefore unidirectional i.e. DC as shown. 21

22 Half Wave Rectifier Power diodes can be used individually as above or connected together to produce a variety of rectifier circuits such as "Half- Wave", "Full-Wave" or as "Bridge Rectifiers". The input power supply may be either a single-phase or a multiphase supply with the simplest of all the rectifier circuits being that of the Half Wave Rectifier. The power diode in a half wave rectifier circuit passes just one half of each complete sine wave of the AC supply in order to convert it into a DC supply. Then this type of circuit is called a "half-wave" rectifier because it passes only half of the incoming AC power supply. Ref: Yrd. Doç. Dr. Aytaç Gören

23 Half Wave Rectifier During each "positive" half cycle of the AC sine wave, the diode is forward biased as the anode is positive with respect to the cathode resulting in current flowing through the diode. Since the DC load is resistive (resistor, R), the current flowing in the load resistor is therefore proportional to the voltage (Ohm s Law), and the voltage across the load resistor will therefore be the same as the supply voltage,vs (minus Vf), that is the "DC" voltage across the load is sinusoidal for the first half cycle only sovout = Vs. Ref: Yrd. Doç. Dr. Aytaç Gören

24 Half Wave Rectifier During each "negative" half cycle of the AC sine wave, the diode is reverse biased as the anode is negative with respect to the cathode therefore, No current flows through the diode or circuit. Then in the negative half cycle of the supply, no current flows in the load resistor as no voltage appears across it sovout = 0. Ref: Yrd. Doç. Dr. Aytaç Gören

25 Half Wave Rectifier The current on the DC side of the circuit flows in one direction only making the circuit Unidirectional and the value of the DC voltage V DC across the load resistor is calculated as follows. Where V max is the maximum voltage value of the AC supply, and V S is the r.m.s. value of the supply. Ref: Yrd. Doç. Dr. Aytaç Gören

26 Half Wave Rectifier with Smoothing Capacitor When rectification is used to provide a direct voltage power supply from an alternating source, the amount of ripple can be further reduced by using larger value capacitors but there are limits both on cost and size. For a given capacitor value, a greater load current (smaller load resistor) will discharge the capacitor more quickly (RC Time Constant) and so increases the ripple obtained. Then for single phase, half-wave rectifier circuits it is not very practical to try and reduce the ripple voltage by capacitor smoothing alone, it is more practical to use "Full-wave Rectification" instead. Ref: Yrd. Doç. Dr. Aytaç Gören

27 Full Wave Rectifier In a Full Wave Rectifier circuit, two diodes are used, one for each half of the cycle. A transformer is used whose secondary winding is split equally into two halves with a common centre tapped connection, (C). This configuration results in each diode conducting in turn when its anode terminal is positive with respect to the transformer centre point C producing an output during both half-cycles, twice that for the half wave rectifier so it is 100% efficient. Ref: Yrd. Doç. Dr. Aytaç Gören

28 Full Wave Rectifier The full wave rectifier circuit consists of two power diodes connected to a single load resistance (R L ) 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 D 1 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 D 2 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. Ref: Yrd. Doç. Dr. Aytaç Gören

29 Full Wave Rectifier As the spaces between each halfwave 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 halfwave rectifier circuit and is about 0.637V max of the peak voltage, assuming no losses. Ref: Yrd. Doç. Dr. Aytaç Gören

30 Yrd. Doç. Dr. Aytaç Gören Using Diode Bridge Rectifier Another type of circuit that produces the same output waveform as the full wave rectifier circuit 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.

31 Using Diode Bridge Rectifier The four diodes labelled D 1 to D 4 are arranged in "series pairs" with only two diodes conducting current during each half cycle. During the positive half cycle of the supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the current flows through the load as shown above. 31

32 Using Diode Bridge Rectifier 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 0.637V max. 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 V MAX amplitude. The ripple frequency is now twice the supply frequency (e.g. 100Hz for a 50Hz supply)

33 Typical Diode Bridge Rectifier

34 Using Diode Bridge Rectifier with 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, there 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 voltage.

35 Using Diode Bridge Rectifier with Smoothing Capacitor As a general rule, we are looking to have a ripple voltage of less than 100mV peak to peak. 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. The main advantages of a full-wave bridge rectifier is that it has a smaller AC ripple value for a given load and a smaller reservoir or smoothing capacitor than an equivalent half-wave rectifier. Therefore, the fundamental frequency of the ripple voltage is twice that of the AC supply frequency (100Hz) where for the half-wave rectifier it is exactly equal to the supply frequency (50Hz).

36 Using Diode Bridge Rectifier with Smoothing Capacitor

37 Using Diode Bridge Rectifier with Smoothing Capacitor 37

38 7805 Voltage Regulator IC Ref:

39 7805 Voltage Regulator IC Ref: 39

40 7805 Voltage Regulator IC

41 41 Yrd. Doç. Dr. Aytaç Gören SMPS Selection What is the voltage and power of the system that you will use it? Voltage: What is the DC voltage needed to run your machine/circuit? Power: DC P [Watt] = V [Volt] x I [Ampere]

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