H2 - AC to DC - DEUkisi.deu.edu.tr/aytac.goren/ELK2018/h2.pdf · 2013-03-21 · • Yrd. Doç. Dr. Aytaç Gören2 W01 Basic Concepts in Electronics W02 AC to DC Conversion W03 Analysis

Yrd. Doç. Dr. Aytaç Gören

H2 - AC to DC

2• Yrd. Doç. Dr. Aytaç Gören

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.

ELK 2018 - Contents

ELK 2018 – W01 Contents

1. AC – Form and values of grid

2. Potentiometer

3. Transformers

4. Semi Conductors

5. Diodes

6. Conversion to DC1. Half Wave Rectifier

2. Half Wave Rectifier with Smoothing Capacitor

3. Using full wave rectifier

4. Using diode bridge rectifier

7. 7805 Voltage Regulator IC

8. Switch Mode Power Supply Selection


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.


Potentiometerhttp://mechatronics.poly.edu/


Potentiometer

Transformers

7

Yrd. Doç. Dr. Aytaç GörenRef: http://www.physics.sjsu.edu/becker/physics51/ac_circuits.htm

Transformers

8


S

P

P

S

P

Strafo

I

I

V

V

N

NK

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 boundsHowever, their ability to conduct electricity can be

greatly improved by adding certain "impurities" to this crystalline structure thereby, producing more free

electrons than holes

Semi ConductorsThe most commonly used semiconductor basics material by far is silicon. Its

atomic number is 14

Silicon has four valence electrons in its outermost shell

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.


Semiconductors- Silicon

Semi Conductors


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

Semiconductor N-type

Semi ConductorsAnother way to make silicon crystal conduct electricity is to add impurity

atoms such as Aluminium, Boron or Indium, which have only three valence electrons

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 "P-type" material with the positive holes

Semiconductor P-Type

Semi Conductors

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


Semiconductor –

PN Junction

Semi ConductorsThis process continues back and forth until the number of electrons which

have crossed the junction have a large enough electrical charge to repelor prevent any more carriers from crossing the junction. Eventually a state of equilibrium (electrically neutral situation) will occur producinga "potential barrier" zone around the area of the junction This areaaround the junction is now called the Depletion Layer.(gerilim seti)


This layer produces a potential difference vallue

of for silicon about 0.6 - 0.7 volts and for germanium

about 0.3 - 0.35 volts. This potential barrier will

always exist even if thedevice is not connected to

any external power source.

Semiconductor –

PN Junction

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 simplestsemiconductor devices, which has the

characteristic of passing current in one direction only

However, unlike a resistor, a diodedoes not behave linearly with respect

to the applied voltage as the diodehas an exponential I-V relationship

PN Junction Diode

Semi ConductorsThere are two operating regions for a diode: Forward biased and Reverse

biased.


When a diode is connected in a Reverse Bias condition, a positive

voltage is applied to the N-typematerial 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 theN-type material and a positivevoltage is applied to the P-type

material.

Operation of a Diode


Diodes

Diodes(open door/closed door)


Diodes(more…)


Leds arealso diodeswhich emitlight.

Diodes

20


The power semiconductor diode, known simply as the Power Diode,has a much larger PN junction area compared to its smaller signaldiode cousin, resulting in a high forward current capability of up toseveral hundred amps (KA) and a reverse blocking voltage of up toseveral thousand volts (KV). Since the power diode has a large PNjunction, it is not suitable for high frequency applications above1MHz, but special and expensive high frequency, high current diodesare available. For high frequency rectifier applications SchottkyDiodes are generally used because of their short reverse recoverytime and low voltage drop in their forward bias condition.


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

Diodes


Half Wave Rectifier

Ref: http://www.electronics-tutorials.ws

Power diodes can be used individually as above or connectedtogether 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 multi-phase supply with the simplest of all the rectifier circuits beingthat of the Half Wave Rectifier. The power diode in a half waverectifier circuit passes just one half of each complete sine waveof the AC supply in order to convert it into a DC supply. Thenthis type of circuit is called a "half-wave" rectifier because itpasses only half of the incoming AC power supply.


Half Wave Rectifier


During each "positive" half cycle of the AC sine wave, the diode is forwardbiased as the anode is positive with respect to the cathode resulting incurrent flowing through the diode. Since the DC load is resistive (resistor,R), the current flowing in the load resistor is therefore proportional to thevoltage (Ohm´s Law), and the voltage across the load resistor willtherefore 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 onlysoVout = Vs.

http://www.electronics-tutorials.ws/dccircuits/dcp_2.html






Half Wave Rectifier


During each "negative" half cycle of the AC sine wave, the diodeis reverse biased as the anode is negative with respect to the cathodetherefore, No current flows through the diode or circuit. Then in thenegative half cycle of the supply, no current flows in the load resistor asno voltage appears across it soVout = 0.


Half Wave Rectifier


The current on the DC side of the circuit flows in one direction onlymaking the circuit Unidirectional and the value of the DCvoltage VDC across the load resistor is calculated as follows.Where Vmax is the maximum voltage value of the AC supply, and VS isthe r.m.s. value of the supply.


Half Wave Rectifier with Smoothing Capacitor


When rectification is used to provide a direct voltage power supply froman alternating source, the amount of ripple can be further reduced byusing larger value capacitors but there are limits both on cost and size. Fora given capacitor value, a greater load current (smaller load resistor) willdischarge the capacitor more quickly (RC Time Constant) and so increasesthe ripple obtained. Then for single phase, half-wave rectifier circuits it isnot very practical to try and reduce the ripple voltage by capacitorsmoothing alone, it is more practical to use "Full-wave Rectification"instead.

http://www.electronics-tutorials.ws/rc/rc_1.html






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.


Full Wave Rectifier


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.


Full Wave Rectifier


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.

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.



The four diodes labelled D1 to D4 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.

• Yrd. Doç. Dr. Aytaç Gören


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. 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)


Typical Diode Bridge Rectifier


Using Diode Bridge Rectifierwith 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 AluminiumElectrolytic 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.



As a general rule, we are looking to have a ripple voltage of less than 100mV peak to peak.

The main advantages of a full-wave bridge rectifier is that it has a smallerAC ripple value for a given load and a smaller reservoir or smoothingcapacitor than an equivalent half-wave rectifier. Therefore, thefundamental frequency of the ripple voltage is twice that of the AC supplyfrequency (100Hz) where for the half-wave rectifier it is exactly equal tothe supply frequency (50Hz).

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.




Using Diode Bridge Rectifier with Smoothing Capacitor

7805 Voltage Regulator IC

Ref: http://www.ti.com/lit/ds/symlink/lm340-n.pdf

http://powersupplycircuit.net/lm7805.html



Ref: http://www.ti.com/lit/ds/symlink/lm340-n.pdf


SMPS Selection

41


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]


Documents

H2 - AC to DC - DEUkisi.deu.edu.tr/aytac.goren/ELK2018/h2.pdf · 2013-03-21 · • Yrd. Doç. Dr. Aytaç Gören2 W01 Basic Concepts in Electronics W02 AC to DC Conversion W03 Analysis