Voltage Controlled Oscillator – Working Principle

What is an oscillator circuit?

Assume an electrical circuit produces the following waveform output (voltage or current output).

Voltage Controlled Oscillator Waveform
Voltage Controlled Oscillator Waveform

This output is a square wave. It can be considered to be a sequence of repeating the following wave at an interval of time period 4.

Voltage Controlled Oscillator
Voltage Controlled Oscillator

This circuit which is producing a waveform by repeating a wave after a specific time interval is an oscillator circuit. Another example can be of a circuit producing continuous sine wave by repeating one cycle of a sine wave.

What is voltage controlled oscillator (VCO)?

The produced continuous waveform produced by the oscillator circuit has a frequency. A circuit in which the frequency of the produced output can be varied by the magnitude of a separately applied external voltage (other than the main supply voltage VCC) is known as voltage controlled oscillator.

Types of VCO:

  1. Linear or harmonic oscillator: This type of oscillator produces a sine wave. It consists of an LC tank circuit or crystal oscillator. The frequency of a tank circuit can be varied by changing the value of the capacitor. Now, a varactor diode’s capacitance can be varied by varying the applied voltage across it. So a varactor diode if used in an LC circuit converts it to a VCO.
  2. Relaxation oscillator: The output signal is a saw tooth or triangularwaveform. This circuit employs the charging and discharging of a capacitor through a resistance. The output frequency depends on the time of charging and discharging of the capacitor.If it is desired to produce a square wave, a triangular wave can be differentiated to produce so. Also a periodic waveform can be passed through a Schmitt trigger to produce a square wave.

IC 566

The IC 566 (or LM566) is an integrated circuit that produces a triangular wave and a square wave output from two different output pins. It is an 8 pin IC shown below:

Pin Configuration

IC 566
IC 566

frequency fo = (2/(R1C1))*((Vcc-Vc)/Vcc)

  1. Ground
  2. No connection
  3. Square wave output
  4. Triangular wave output
  5. Modulating/Control voltage VC
  6. Timing resistor R1 (connected between pin 6 to supply voltage VCC)
  7. Timing capacitor C1 (connected between pin 7 to ground)
  8. Supply voltage VCC

A rough internal circuit is shown below:

Voltage Controlled Oscillator
Voltage Controlled Oscillator

Basically, the principle of operation is as such:

The Schmitt trigger switches the current source from charging and discharging the capacitor.

The IC charges and discharges the external capacitor C1 through the resistor R1. A triangular waveform is obtained by passing the voltage waveform across the capacitor C1 through Buffer Amplifier 2 and obtained as output through pin 4.

The voltage waveform across the capacitor when passed through a Schmitt trigger, produces a square wave which is passed through the Buffer Amplifier 1 and obtained as output through pin 4.

Modulating voltage VC should be in the range of  (3/4)Vcc < Vc < Vcc where VCC is the supply voltage.

VCC should be within 10 to 24 Volts.

The frequency modulation (by applying a varying modulating voltage VC) can be done in 10:1 ratio.

The frequency of the output waveform is f0 = (2/R1C1)*((Vcc – Vc)/Vcc) .

An example circuit is shown below:

Voltage Controlled Oscillator
Voltage Controlled Oscillator

Applications of VCO

  1. Tone generators
  2. Frequency modulation
  3. Function generator
  4. Phase Locked Loop

This article is written by Sayantan Roychowdhury.

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Series Voltage Regulator – Working Principle

We assume that the voltage across a zener diode remains constant.

i.e. DVZ = 0.

In all cases, we indicate load resistance by RL

Series voltage regulator circuit diagram
Series voltage regulator circuit diagram
  • Assume supply voltage increases by DVS

Current through resistance R is IR = (VS-Vz )/R

or, DIR = DVS / R                                (Equation 1.1)

Also IR = IB + IZ ;  or, DIR = DIB + DIZ ;            (Equation 1.2)

From Equation 1.1 and Equation 1.2, an increase in VS increases base current IB and zener current IZ. Since collector current IC = ß*IB so IC also increases.

We know IE = IB + IC;

or,          (since IB is very small compared to IC)

DIE = DIC

As IC increases, IE will also increase through load RL, thus voltage output VO = IE*RL tends to increase.      (Effect 1: VO tends to increase)

Using KVL in output circuit, VO + VBE – VZ = 0; where VBE = base emitter voltage, VZ = zener voltage

DVO = -DVBE        (Equation 1.3)

Equation 1.3 suggests, an increase in output voltage VO decrease base emitter voltage VBE. As decrease in VBE causes decrease in IC , and conversely IEthrough RL , hence output voltage VO tends to decrease.             (Effect 2: VO tends to decrease)

Effect 1 and Effect 2 neutralise each other and VO is constant.

Opposite happens when VS decreases.

  • Assume supply current IS increases by DIS (keeping VS constant)

IS = IC + IR; or, DIS = DIC + DIR         (Equation 2.1)

IR = IB + IZ; or, DIR = DIB + DIZ         (Equation 2.2)

From Equation 2.1, IS increases IC (also IR). Also this is evident as from Equation 2.2, that increase in IR increases IB and hence increases IC.

As IE˜IC so IE increases through RL. Hence output voltage VO = IE*RL tends to increase.

(Effect 1: VO tends to increase)

Remaining analysis is similar to previous case. VO tends to increase decreasing VBE (like Equation 1.3). This decreases IC, consequently decreasing IE and this tends to decrease VO.

(Effect 2: VO tends to decrease)

Effect 1 and Effect 2 neutralise each other and VO is constant.

Short circuit protection

To prevent short circuit i.e. to prevent an excessive high flow of current, the following arrangement is made.

Short circuit protection
Short circuit protection

A very small resistance RSC is connected in series with the load. The base emitter terminals of BJT Q2 are connected across this RSC resistance. When a high current flows across the load, an appreciable amount of voltage is developed across RSC. Hence base emitter voltage of Q2 increases, collector current of Q2 increases, so IB is shunted away from Q1. As IE˜IC= ß*IB , hence IE decreases and a large current flow is prevented.

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Shunt Voltage Regulator – Working Principle

A zener diode forms an integral part of any voltage regulator. Before we go ahead, we know, that in all cases, the voltage across a zener diode will remain constant. i.e. ?VZ = 0. In all cases, we indicate load resistance by RL.

Regulator using zener diode only

Regulator using zener diode only
Regulator using zener diode only
  • Across RL we have: VO­ = VZ = ILRL                                            (Equation 1)
  • From current law: I = IZ + IL                                                          (Equation 2)
  • From KVL along indicated path: VS = I*R + VZ                             (Equation 3)

Equation 1 tells that output voltage VO will always be constant = VZ.

Assume two cases:

  • Assume supply current I change by dI
    From Equation 2: ?I = ?IZ + ?IL
    From Equation 1: ?VZ = ?ILRL ; or, ?IL = 0 (since ?VZ = 0)
    Thus ?I = ?IZ. This shows that excess current is bifurcated through the zener diode.
  • Assume load RL changes by ?RL (with VS constant)
    Output voltage VO will remain constant, but change in IL will be compensated by change in IZ
    From Equation 3: ?VS = ?I*R+ ?VZ ;      or, 0 = ?I*R + 0 ;               or, ?I = 0
    From Equation 2: ?I = ?IZ + ?IL ;            or, 0 = ?IZ + ?IL  ;             or, ?IL = – ?IZ

Thus if IL increases, IZ decreases and vice versa.

Regulator using transistor and zener diode

Regulator using transistor and zener diode
Regulator using transistor and zener diode

Few points:

Correlating VO and indicated path from point X to GND: VO = VX = VZ + VBE          (Equation 1)

I = IB + IC + IL ;   or, I = IC + IL(since IB is very small)                                                     (Equation 2)

The increase in VBE causes more collector current IC to flow.

  • Assume current I increase by dI keeping VS constant (opposite analysis will take place of I decreases)?I is positive. VS – I*R = VX ;         or, 0 – ?I*R = ?VX ; (since VS is constant)
    i.e. VX = VO  decreases on increase in I.                                                                  (Effect 1: VO tends to decrease)Next, from Equation 1: ?VO = ?VZ + ?VBE ;            or, ?VO = 0 + ?VBE ;
    i.e VBE also decreases on decrease in VO
    As VBE decreases, IC decreases.From Equation 2: ?I = ?IC + ?IL
    If ?I = positive (assumed);           ?IC = negative (as VBE decrease);           so IL must increase.
    The voltage across load VL = IL*RL increases.                                                       (Effect 2: VO tends to increase)The Effect 1 and Effect 2 neutralize and VO is constant.
  • Assume supply voltage VS is increased keeping current I constantThe analysis will take place just as done previously.
    VS – I*R = VX ;    or, ?VS – 0 = ?VX ; (since I is constant)
    i.e. VX = VO increases on increase in VS.                                                                 (Effect 1: VO tends to increase)Next, from Equation 1: ?VO = ?VZ + ?VBE ;            or, ?VO = 0 + ?VBE ;
    i.e VBE also increases on increase in VO As VBE decreases, IC increases.From Equation 2: ?I = ?IC + ?IL
    If ?I = 0 (assumed);         ?IC = positive (as VBE increase);  so IL must decrease.
    The voltage across load VL = IL*RL decreases.                                                     (Effect 2: VO tends to decrease)
    The Effect 1 and Effect 2 neutralize and VO is constant.

This post is written by Sayantan Roychowdhury. If you like this article, please share it with your friends and like or facebook page for future updates. Subscribe to our newsletter to get notifications about our updates via email. If you have any queries, feel free to ask in the comments section below. Have a nice day!

Linear Voltage Regulator – Series and Shunt type

Hi friends, in this article, we will take a basic overview of a linear voltage regulator and its types. This includes the block diagram and working principles.

What is voltage regulator?

A voltage regulator prevents the varying of the voltage across a load in spite of variation in the supply. It is also used to regulate or vary the output voltage of the circuit.

Two terms:

  • Regulation: compensates for variation in the mains (line voltage)
  • Stabilization: compensates for variation in load current

However, in practice, both the terms loosely used for the same meaning of voltage regulation.

Types of voltage regulator

There are mainly two types:

  1. Series voltage regulator
  2. Shunt voltage regulator

Series voltage regulator:

A simple block diagram is as follows

Series voltage regulator
Series voltage regulator

The series voltage regulator controls variation in voltage (DVS) across the load by providing a voltage in series with the load.

A further more detailed block diagram is shown. A series regulator has its regulating unit in series with the load.

Series voltage regulator
Series voltage regulator

There is always a voltage drop in the regulating unit (VR). The output voltage VO (or VL) is:

VL = VS – VR

Series voltage regulator usually has a negative feedback system. If load voltage (VL) tends to fall, smaller feedback decreases controlling unit resistance thereby allowing more current to flow in the load (VR decreases) and increasing VL. Opposite happens when VL increases.

Shunt voltage regulator

Block diagram is as follows

Shunt voltage regulator
Shunt voltage regulator

Shunt voltage regulator controls the voltage across the load by varying the current flowing through the load (IL) and through the regulating unit (IR).

A further detailed block diagram is shown below. A shunt regulator has its regulating unit in parallel to the load.

I = IR + IL

The stability in the voltage across the load RL is brought about by ensuring a steady current flow through it.

When the current across RL tends to increase, regulating unit prevents it by allowing the excess current to flow through it. Since current I is constant, IL decreases.

Same happens when current IL tends to decrease. Regulating unit prevents it by decreasing current flow (IR) through it, thereby increasing IL.

This article is written by: Sayantan Roychowdhury

Tags: LM317, adjustable voltage regulator, zener diode voltage regulator, voltage regulator 7805, vrm, avr, ldo.

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How To Build Home Made Electric Fan Regulator – Mini Project

Hi friends, in this article we will see one simple mini project for electronics and electrical engineering students. We all are familiar with electric fan regulator which we use for varying the fan speed. The basic principle behind regulator is a change of resistance.

This article is written by Mohamed Maricar & Modified by Mayuresh Joshi

Cheap and Best Electrical Fan Regulator

Electric Fan Regulator

Fig (A): shows the full view of connection diagram of the product
full-view-of-electric-fan-regulator
Fig (B): shows full view of the product and external side
PCB-Without-Resistance
Fig (C): shows the PCB without resistance

 

Components required:

  1. One Resistance = Rs. 0.15
  2. 28 Resistances = Rs.4.20
  3. One PCB = Rs.5.00
  4. One Rotator Switch = Rs. 8.00
  5. One Plastics Cabinet = Rs.5.00
    Total Cost = Rs. 22.20 Rupees Only

Steps to build electric fan regulator:

  1. First, we have to take PCB as shown in Fig (C)
  2. Then we put the Resistance and solder in PCB holes as shown in fig(A)
  3. Now we connect PCB ends with rotator switch as in fig (A)
  4. We connect rotator switch with AC supply
  5. Now if we vary the rotator switch we can get the different speed of motor
    1. The Resistance network is used to drop the voltages in five steps that are level
    2. The first step 13 volts dropped second steps 26 v third step 39v fourth step 53v
    3. By dropping the five level used to vary the speed of motor
    4. By dropping voltages we can vary the speed of electrical fan motor
  • What is my idea?
    My idea is to design a new circuit to reduce the cost and increase the performance of the product
  • What does it do?
    It regulates the speed of electric fan motor by dropping a.c. voltage in different level
  • How does it work?
    It is working by Ohms law and circuit theory principles
  • What makes my idea Unique?
    Cheap and best

Advantages of my product

  1. Cheap cost
  2. Low care
  3. Low power loss
  4. Low heat loss
  5. Good performance

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Fastest Finger First Circuit Without using Microcontroller

Now a days quiz-type game shows are increasingly becoming popular on television. In such quiz games, fastest finger first indicators (FFFIs) are used to test the contestant’s  reaction time. The player’s designated number is displayed with an audio alarm when the player presses his entry button.

Fastest Finger First Project

The fastest finger first circuit presented here determines as to which of the four contestants first pressed the button and locks out the remaining three entries of other three members. Simultaneously, an audio alarm (buzzer) and the correct decimal number display of the corresponding contestant are activated.

Fastest finger first
Fastest finger first

Components used

  1. Resistors: 1KO, 330O, 100KO, 10O, 10KO
  2. Ceramic Capacitors: 0.033uF, 0.01uF, 0.047uF
    Electrolytic Capacitors: 47uF (35V)
  3. Miscellaneous: Common anode seven segment LED display
  4. S1-S5: Push button (Switches), Speaker (8O, 1W)
  5. Integrated circuits:
    IC 7805     ….voltage regulator
    IC 74LS75 …. 4-bit bistable latch
    IC 74LS20 …. Dual 4 input NAND gate
    IC 74LS147 …. 9 lines to 4 lines priority encoder
    IC 74LS04 …. HEX inverter
    IC 74LS47 …. BCD to seven segment decoder
    IC NE555 …. Timer

Working of Fastest Finger First Indicator:

When a contestant presses his switch, the corresponding output of latch IC2 (7475) changes its logic state from 1 to 0. The combinational circuitry comprising dual 4-input NAND gates of IC3 (7420) locks out subsequent entries by producing the corresponding appropriate latch-disable signal. Priority encoder IC4 (74147) encodes the active-low input corresponding audio oscillator.binary coded decimal (BCD) number output. The outputs of IC4 after inversion by inverter gates inside hex inverter 74LS04 (IC5) are coupled to BCDto-7-segment decoder/display driver IC6 (7447). The output of IC6 drives common anode 7-segment LED display (DIS.1, FND507 or LT542). The audio alarm generator comprises clock oscillator IC7 (555), whose output drives a loudspeaker.

The oscillator frequency can be varied with the help of preset VR1. Logic 0 state at one of the outputs of IC2 produces logic 1 input condition at pin 4 of IC7, the audio oscillator IC7 needs +12V DC supply for sufficient alarm level. The remaining circuit operates on regulated +5V DC supply, which is obtained using IC1 (7805). Once the organizer identifies the contestant who pressed the switch first, he disables the audio alarm and at the same time forces the digital display to ‘0’ by pressing reset pushbutton S5. With a slight modification, this circuit can accommodate more than four contestants.

Conclusion:

This project is an electronic quiz buzzer. Fastest finger first indicators are used to test the player’s reaction time. The player’s designated number is displayed with an audio alarm when the player presses his entry button. In the buzzer round of quiz contest, the question is thrown to all the teams. The person who knows the answer hits the buzzer first and then answers the question. Sometimes two or more players hit the buzzer almost simultaneously and it is very difficult to detect which of the team has pressed the buzzer first. In television shows, where the whole event is recorded, the actions are replayed in slow motion to detect the first hit. Such slow motions are possible only where huge funds are available to conduct the show. For this reason, buzzer rounds are avoided for quiz contests held in colleges.

But this indicator reduces the probability of any error in detecting who pressed the buzzer first. Thus, in this project, we have concluded all the components for the setup of this indicator.

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Tags: Fastest Finger First Project report pdf. ppt.