Zener Diode As Shunt Regulator

Voltage regulator provides regulated output whether load current or input voltage is changed or not . Zener Diode completes this task very well. As these diodes work in breakdown region that is why they are used as voltage regulators. A simple Zener Voltage regulators is shown in the diagram given below.

Here ‘Vin’ in input DC voltage in which the occurred changes are to regulate. Zener diode is installed across ‘Vin’ in reverse direction. And load resistance (RL) is applied across Zener diode . Constant Voltage are required across ( RL) when the value of supply voltage ‘Vin’ increases from zener voltages (Vz) then the diode conducts and a large Current flows through series resistance ( Rs) , that is equal to the sum of diode current ( Iz) and load current ( IL) .

I = IL + Iz

“At Every State “     Vout = Vz

And                                       Vin = IRs + Vout

Putting the value of V out

                                            Vin = IRs + Vz

1) 1st Condition:

      Suppose that (RL) is constant and supply voltage (Vin) is increased. is this condition the reverse current (Iz) flow in very low value until the breakdown voltage. But when the (Vin) increases then breakdown voltage then Internal resistance of zener diode decreases and (Iz) increases rapidly due to this , the total current I is also increases thus voltage drop across series resistance Rs also increase

Hence output voltage remains constant , because

V out =  V in – Irs

Opposite to this, if the value of (V in) is decreased then a low current flows through diode. In this way, the total current ‘I’ also decreases and as a result low voltages are dropped across ‘Rs’ so output voltage still remains constant .

2^nd Condition:

Suppose that (Vin) is constant but diode current (Iz) changes when load current (IL) increases then (Iz) decreases but current I doesn’t change an output voltage still remain constant in this condition because

V out = vin – Irs

=Vin – (Iz + IL) Rs since (I = Iz+ IL)

Similarly when IL decreases then (Iz) is increases but current I doesn’t change and output voltage still remains constant in this condition.

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Rating and Uses of Zener Diode

i)             Voltage Rating :

    Rating of zener diode is explained with respect to its zener voltage .(Vz).

Commonly , the zener diodes having zener rating of 1.8 volt to 2.00 volts are available in the market whose tolerance is 5 percent to 10 percent and sometimes upto 20 percent . anyhow , zener voltage depends upon doping level and temperature .

ii)            Power Rating :

Power rating of zener diode is a product of zener voltage and zener current .

Mathematically :

Pz = Vz   x  Iz

The power rating of common zener diode can be 150 m watt to 50 watt .

Uses of Zener Diode:

Zener Diode are used at a vast level in transistor circuitry , out of which few uses given below.

1. As a voltage regulator.
2. For protection from high voltage in meters.
3. To reshape a wave .
4. As peak clippers or voltage limiters .
5. For biasing and comparing in a network and to calibrate volt metes as a fixed reference.

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Zener diode

Zener diode

It is a heavily doped PN junction made of Germanium or Silicon and works

At the breakdown region  in reverse bias condition zener diodes are commonly made of Si instead of Ge because Si has the ability to bear more current and temperature. It is just like the common diode , only the two ends of the line that shows cathode are bended .As shown as figure.

Working Principle & V/I characteristics:

When the zener diode is forward biased , then the resistance o-f the circuit is low. And this works as a common silicon diode at a voltage of 0.7 v (0.3 v for Ge). Its Forward Current starts to increase rapidly. As shown in the curve given below.

When it is reverse biased then  the resistance of circuit is very high . and a low value of reverse current flows through it ( Leakage Current ).

When its reverse voltages are further increased then at a certain point the junction is break down and reverse current increases rapidly , whose value is limited by applying an external resistance in series o-f junction .

A critical value of voltage at which this condition occurs is known as breakdown voltage.

If the voltage is further increased  then the current increases rapidly while the voltages in the breakdown region , almost stable as shown in the curve.

Zener Biasing:

For the proper function of a zener diode , its biasing must be proper .thus , during the biasing of zener diode , following points should be taken care of :-

1. Zener diode must be always reverse biased .
2. Its parallel reverse voltages must be always higher than (Vz).
3. its should be installed in a circuits in which current flows less than ( Iz max).

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Photo Diode

Photo Diode

Photo diode is a PN junction device that works in the ‘reversed biased’ condition when light falls on it

Advantages

These are small in size and durable

Their life time is very long

These are more efficient

Circuit diagram:

Symbol:

Construction:

A photo diode is construct just like a semiconductor conventional PN junction diode. Except one thing, that a transparent Lenz is attached over its PN junction to focus light rays on it. Light passes through this transparent Lenz and falls on PN junction.

Operation of photo diode

Photo diode normally operates in reverse bias mode.

We know that when a junction is reverse biased than ‘reverse saturation current’ passes through the junction, that flows due to pairs of holes & electrons produced due to heat.

When small amount of is light is falling on the junction, then it resistance is very high, at this condition, a minor current passes through junction that is called ‘dark current’

But when the intensity of light increase, the minority carriers obtain thermal energy.

As a result, the resistance of junction is decreased and high quantity of covalent bond breaks, it means more pairs of holes and electrons are produced and reverse current is increase.

As the light intensity increases in same speed

Materials used for photo diode

(Photo diode _ conductive materials)

Cadium sulphide

Cadium selenoide

Cadium taloride

Lead sulphide

Thallium sulphide

Selenium

V/I Characteristics curves:

Uses

Detection

Demodulation

Switching

Optional communication devices

Encoder

CD players

Punched card readers

Movies devices

Logic circuit

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B.J.T as Voltage Amplifier

B.J.T as Voltage Amplifier

If a weak electrical signal is provided between the two input terminals of the transistor, then it amplifies the strength of the transistor, then it amplifies the strength of the signal. Thus an amplified signal is obtained across two output terminals of transistor. This process is known as amplification.

Thus, amplification is a process in which amplitude of an electrical signal over output of transistor is increased in linear style. However, diagram of output waveform is similar to diagram of input waveform. Only the amplitude of input signal is changed on reaching output.

Since the voltage amplification depends upon output resistance (its value is very low), so the value of output voltage is very high as compared to the value of input voltage. This should be kept in mind that when a transistor is to be used as amplifier, then it should be biased in its active or linear region.

There are three terminals of a transistor. Its one terminal is used for input, second for output, while third works as grouped, which is common for input & output terminals.

When a transistor is to be used as an amplifier, then it is connected in one of these three configurations.

                  i.        Common-Base Amplifier

                ii.        Common-Emitter Amplifier

               iii.        Common-Collector Amplifier

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Operation Modes of BJT

Operation Modes of BJT

There are two junctions in bipolar junction transistor (B.J.T), which are separately forward or reverse biased. So, in this way, four operating modes of a B.J.T are found. (It means a B.J.T can operate in four different modes). These modes are named as:

1-   Forward active

2-   Cut Off

3-   Saturation

4-   Reverse Active

1.          Forward Active.

 In This Mode of Operation of Transistor, Emitter-base junction is reverse biased. Due to this configuration the transistor works as a controlled source in its forward active or linear mode. Due to its controlled characteristics, a B.J.T can be used as an amplifier in analogue circuits.

2.          Cut-0ff.

When Both Junctions of Transistor are reverse biased, then this mode of transistor is known as cut-off. In this situation, transistor works as an open switch (means, turned to off condition) and value of the current passing through it is almost zero.

      In this mode of operation, a B.J.T can be used for switching in computer and

      digital circuits

3.          Saturation.

In this operation mode of transistor, its both junctions are forward biased. As a result, when low voltages are applied parallel to collector-base junction, a large amount of collector current passes through transistor. Thus, in saturation mode, a transistor works as a closed switch (means turned to ON condition) in this mode of operation; a B.J.T can be used for switching in computer and digital circuits.

4.          Reverse Active.

In a transistor, if emitter-base junction is reverse biased and collector-base junction is forward biased (operation to forward-active mode) then such operating mode of transistor is known as reverse-active. This mode is also called inverted-mode. Practically, this mode is not useful for amplification due to a large flow of collector current (because a transistor can become useless due to this type of biasing).

However, Reverse-active mode is used in digital circuits and certain switching analog circuits.

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LCD (Liquid Crystal Display)

Definition

Liquid Crystal is substances that have the ability of reflection and its ability change according to applied voltage to it.

LCD    (liquid crystal display)

LCD is a device that consist of liquid and it

Display information on liquid display.

Construction of LCD

A thin layer liquid crystal is sandwiched between two sheets of glass(the thickness of liquid crystal layer is 10 to 20um).To provide electric field parallel to crystal ,a transparent conducting materiel is applied to inner surface to glass sheet.

Whenever it needed to change the molecular structure of liquid crystal, then this crystal is connected to external voltage through that conducting material.

       Stannic Oxide (Sn02) and Oxide (In2O3) are used to make electrodes.

     Whenever the electric field is present at liquid,

It because opaque.

Thus when voltages are applied to liquid crystal .it does not reflect light.

Display patterns similar LEDs can be created by organizing the molecular into circles. So for application of LEDs the LCD can be also used.

Comparison between LED and LCD

            LED                                                                        LCD

1 It is PN junction diode. 2    It works on the principle of emission light()it produce and emit light). 3  It required more current for operating(nearly 20mA). 4  it works on DC voltage. 5 Consume more power. 6 Response time is less, usually 100 nano second. 7   These are speed. 8 These have lower life. 9  These can be used where power consumption is not a problem. 10  Heavier in weight.

1  It is not a diode. 2  It  works on the principle of reflection of light(it only reflect of light or change its condition). 3  it required less current (about 30 uA). 4  It works on AC voltage of the form of sin wave or square wave (30Hz) . Because if DC is provided, then its life decreases. 5 Consume less power. 6 response times is longer, ussally100 to 300 mile – second. 7 There speed very low. 8 These have longer life. 9  Mostly used in less power devices watch, clocks etc. 10   Lighter is weight and smaller.

Uses of LCDs

Due to consuming very low power to produce electric field, LCDs are commonly used in

1 Pocket size calculators.

2 Digital clocks.

3  Portable computers.

4  Electric type – write display.

5 Small television screens.

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Switch logic: OR and AND

The following diagrams are the first circuits we explore: an OR circuit and an AND circuit.
While the diagrams are drawn as if these are electrical circuits (a light goes on if the correct
switches are closed), we actually demonstrated these with a water circuit, consisting of a
reservoir on top, a catch basin at the bottom, tubes instead of wires, and valves for switches.
George Boole’s switch logic works for water just as it does for electricity!
For the diagrams below, imagine a teacher asking a question. If they think the answer is “Yes”,
then the students press a switch on their desk.
In the OR circuit, if either Annie or Bert say “Yes” (press their switch) then the light goes on.
(It also works if they both press their switch).
In the AND circuit, both Annie and Bert have to agree that the answer is YES, and both have to
press their switches for the light to go on.


Examples of OR circuits:
Ÿ Electric car windows: either the driver or a passenger can open the passenger’s side window.
Ÿ Interior light in a car: goes on when any door is opened (driver’s side door or passenger’s
side door or driver’s side back door or ...). But you have to think a little: when the car door
is opened, an electrical switch (usually in the door jamb) is actually closed to allow the
current to flow to light up the lamp. Can you find those light switches on your car?


Example of AND circuit:
Ÿ Again the electric car window: a master switch (at the driver’s seat) has to be on and a local
switch needs to be pressed for the window to operate.


The “SAME” circuit above is a combination of AND and OR. The effect is that the light will be
on if Annie and Bert both say “yes”, or both say “no” to a teacher’s question, in other words, if
they both agree. The logic is: (yes_A AND yes_B) OR (no_A AND no_B).
This is also known as an “equivalence” circuit.
If the yes_A and no_A switches were reversed, then this would be a “NOT-THE-SAME” circuit
(no_A AND yes_B) OR (yes_A AND no_B). Such a circuit is also known as an
“exclusive OR”: The light goes on if Annie OR Bert says yes, but not both (they disagree -- just
as you would expect from Annie and Bert!). An abbreviation for “exclusive or” is XOR, and it
turns out that this is a very handy circuit to have around.
“Same” or “not-the-same” circuits are used wherever a computer makes comparisons.
Another example of a “SAME” circuit (though wired differently): hall lights in a house with an
upstairs and downstairs switch.
The other circuit, above on the right, looks very similar. The difference is who controls the
switches. In the “CHOICE” circuit, the top two switches are controlled by the teacher, who
makes to choice to listen to Annie or to listen to Bert. If the teacher switches on Annie, then
Annie can answer a question by pressing her switch, and Bert’s answer is ignored. And the other
way round.
The fancy name for such a circuit is a “multiplexer”, and it is used wherever a choice is made in
a logic circuit.

With AND and OR gates, almost any logic can be made. The missing element is a NOT.
For example, in the choice circuit above, a NOT circuit could be connected between the
Listen_A and listen_B switches, so that at any time one is closed, and the other is open
(thus, the teacher listens to Annie or to Bert, but cannot switch them both off).
With just AND, OR and NOT, any logic circuit can be made!

Look Ma, no fingers...
How does this work in electronics, without lots of fingers to push lots of switches?
Well, the switches are special. They are called transistors, and work with electrical voltages
acting as the “fingers” pushing them open or closed.
As if, in the circuits above, the light from the lamp would push on a switch in the next circuit,
and that one on the next, and the next.... Only, no lamps either. Only voltages and currents.
Exactly how all that works does not matter, though. Switch logic works as well with water valves
as it does with finger-actuated switches, as it does with transistors.
(It is just that transistors are faster.... much, much faster...).

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What do computers do?

We use computers for a lot of things. Playing games, writing book reports, calculating math
problems... It actually all started with math problems.
Ÿ So these boxes can calculate quite well. Very well.
Ÿ We do know that they do what they are told. You push a button, and the computer does it.
It does exactly what you tell it to do (which is not necessarily what you meant it to do...).
It follows instructions.
Ÿ Computers move information, for example your book report from the disk to the printer.
Or a file from the Internet to your display screen, or to your own hard disk. They store
information (all the book reports you have written are stored on the hard disk), and they
manage it (you can find it again).
How do those silicon switches we talked about actually make all this happen?
This class is going to explore just that: how we can do cool things, such as writing text, making
pictures and calculating with switches. Just like computers do.
This is called switch logic, or Boolean logic, after George Boole (English mathematician,
1815-1864), who was the first to think of it -- long before electronics existed!

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How are computers made?

We started by showing the stuff that computers are made of. It all begins with common sand,
which consists mostly of silicon dioxide (quartz). Using chemical methods, the sand is converted
to pure silicon. Very pure silicon, 99.999 999% -- you can’t get anything more pure.
Pure silicon is a funny material. It shines like a metal, but is breakable like a ceramic. It is a
semiconductor. That means it is on the edge: does it conduct electricity or doesn’t it? Well, we
can make it do both: make it conduct, or make it stop conducting.We can switch an electrical
current in silicon on or off, at will, and very, very fast. From silicon, we make fast switches!
A whole bunch of those switches together make a chip, which is put inside a plastic cover.
A bunch of chips are mounted on a printed circuit board.
A bunch of boards make an electronic box: a VCR, a TV, a radio, a computer.
Well, of course you need more stuff, like a power supply, a display, a hard drive, and a box to fit
it all in. But the heart of anything electronic is those silicon switches.

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The OR and XOR Gates

The OR gate is also a two-input, single-output gate. Unlike the AND gate,

the output is 1 when one input, or the other, or both are 1. The OR gate

output is 0 only when both inputs are 0.

A	B	Q=A AND B
0	0	0
0	1	1
1	0	1
1	1	1

A related gate is the XOR, or eXclusive OR gate, in which the output is 1

when one, and only one, of the inputs is 1. In other words, the XOR output

is 1 if the inputs are different.

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The AND Gate

A basic AND gate consists of two inputs and an output. If the two inputs

are A and B, the output (often called Q) is “on” only if both A and B are

also “on.”

In digital electronics, the on state is often represented by a 1 and the off state

by a 0. The relationship between the input signals and the output signals is

often summarized in a truth table, which is a tabulation of all possible inputs

and the resulting outputs. For the AND gate, there are four possible

combinations of input states: A=0, B=0; A=0, B=1; A=1, B=0; and A=1, B=1.

In the following truth table, these are listed in the left and middle columns.

The AND gate output is listed in the right column.

Table 1Truth Table for AND Gate

A	B	Q=A AND B
0	0	0
0	1	0
1	0	0
1	1	1

In LabVIEW, you can specify a digital logic input by toggling a Boolean

switch; a Boolean LED indicator can indicate an output. Because the AND

gate is provided as a basic built-in LabVIEW function, you can easily wire

two switches to the gate inputs and an indicator LED to the output to

produce a simple VI that demonstrates the AND gate.

                      Figure 1 LabVIEW AND Function Wired to I/O Terminal Boxes

Run AND gate.vi from the Chap 1.llb VI library. Push the two input buttons

and note how the output indicator changes. Verify the above truth table.

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Introduction to Digital Electronics

Digital electronics is one of the fundamental courses found in all electrical

engineering and most science programs. The great variety of LabVIEW

Boolean and numeric controls/indicators, together with the wealth of

programming structures and functions, make LabVIEW an excellent tool to

visualize and demonstrate many of the fundamental concepts of digital

electronics. The inherent modularity of LabVIEW is exploited in the same

way that complex digital integrated circuits are built from circuits of less

complexity, which in turn are built from fundamental gates. This manual

is designed as a teaching resource to be used in the classroom as

demonstrations, in tutorial sessions as collaborative studies, or in the

laboratory as interactive exercises.

The order of the labs follows most electronic textbooks. The first six labs

cover the fundamental circuits of gates, encoders, binary addition,

D-latches, ring counters, and JK flip-flops. Many of the VIs are suitable for

both classroom demonstration and laboratory exploration.

The second set of six labs cover advanced topics such as DACs, ADCs,

seven-segment displays, serial communication, and the CPU. These are best

done in the context of a digital electronics lab, comparing the LabVIEW

simulations with real integrated circuits. In each case, you can enhance

simulations presented in the text by using a National Instruments DAQ

board to interact with the real world through LabVIEW digital I/O, analog

out, analog in, and serial VIs.

Labs 2, 5, and 12 are application oriented and are designed to demonstrate

encoding schemes, digital encryption, and the operation of a CPU. These

labs could be presented as challenging problems in a tutorial setting or in a

workshop environment.

The labs can also be grouped to demonstrate special relationships of

advanced devices on certain basic gates. For example, the CPU operation is

dependent on the concept of registers and two input operations.

This manual includes a complete set of LabVIEW VIs. The text is also

included on the CD so that you can customize the material.

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Characteristics of a Common Emitter (CE) Amplifier

(1)             Its input resistance is less up to a specific limit (1K to 2K)

(2)             Its output resistance is high up to a proper limit (50K or above)

(3)             Its current gain (B) is high (50 to 300 times)

(4)             Its voltage gain is very high (1500 or more)

(5)             It produces a big power gain (10,0000 times or 40 db)

(6)             It produces “Phase Reversal” of input signal. It means that input signal and output signal are produced at a difference of 180 degree to each other.
Related:
Common Emitter (CE) Amplifier
Circuit Operation of Common Emitter (CE) Amplifier

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Circuit Operation of Common Emitter (CE) Amplifier

When the positive half-cycle of signal is provided

(1)             As the base of transistor is already positive relating to biasing, so voltage (VBC) increases.

(2)             Due to increase in VBE , the forward bias of Emitter-base junction also increases.

(3)             IB is also slightly increased.

(4)             As a result of increase in IB (Base Current), the IC (Collector Current) increase up to B times as (IC = BIB).

(5)             Due to increase of IB , a large increase in ICRC drop occurs.

(6)             VCE decreases according to following equation.

VCE = VCCICRC

Thus, negative half-cycle of input is achieved. It means that when positive input signal is provided to such circuit, then the amplified output signal is negative, (as shown in figure)

When negative half-cycle is provided to input then the achieved output cycle is positive.

    Related:

      Common Emitter (CE) Amplifier

       Characteristics of a Common Emitter (CE) Amplifier

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Common Emitter (CE) Amplifier

When a transistor is added to a circuit such that, input signal is provided parallel to its emitter-base junction and output is obtained from collector-emitter junction while emitter is common or grounded then such circuit is called common-emitter circuit. This circuit is the most popular method to use transistor as an amplifier.

In other words, “common-emitter circuit” is a circuit in which:

        1.     Emitter is grounded

        2.     Input signal is provided across base

        3.     And output signal is obtained across collector

A signal stage CE amplifier circuit is shown, in the figure, in which NPN transistor is used.

Base is ‘driven element’ in it (it means that base current plays the role of input)

 Input current is provided through base-emitter circuit while, output signal is obtained through collector-emitter circuit.

Emitter base junction is forward biased with battery VB and collector-base junction is reverse-biased with battery VCC. 

       Related:

         Circuit Operation of Common Emitter (CE) Amplifier

          Characteristics of a Common Emitter (CE) Amplifier

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