FAMILIARISATION OF OP-AMP

Operational amplifier, in short , op-amp is a versatile device used to amplify AC and DC signal. Though it was originally designed for computing mathematical operations such as addition, multiplication, differentiation, integration etc., it is widely used for veriety of applications like oscillators ,fillters regulators, clipping circuits waveform generators etc.
The symbol of op-amp represent a circuit with two input , an output terminal and two bias supply points.
The 741 it is frequency compensated and shot circuit protected IC. 741C is its commertial version of the operating temperature range from 0 to +70degree C.
741 need +ve and -ve dc source for bias supply connections V+ and V- . This is provided by either a dual power supply or two power supplies. When dual power supplies used its positive terminal.is connected to V+ pin of the ic and -v terminal is connected to V- pin of the IC. The ground terminal of the dual power supply is connected to the ground point of the circuit. When two power supplies are used +ve terminal of the power one  supply and -v terminal of other supply are connected to V+ and V- pins of IC rspectivly. Remaining trminals of the power supplies are connected ti the groun point.of the circuit. When several op-amp are used in a circuit, one power supply is enough to drive all op-amps because of the low power consumption of op-amps.
The output saturation voltages in general are about 2V below the magnitude of the dc power supply levels.

MONSTABLE MULTIVIBRATOR USING 741 OP-AMP

Monostable multivibrator is also called one shot. It has a tsable state and a quasi stable state . The circuit remains in the stable state until triggering signal causes a transition to quasi stable state after a time intervell , it returns to the stable state so a single pulse is generated when a trigger is applied.
consider the instant at which the output Vo=Vsat . Now the diode D1 clamps the capacitor voltage Vc at 0.7V feed back voltage available at nin inverting terminal is +betaVsat . When the negative going triger is applied   such that the potential of non inverting terminal become less than 0.7V , the output switch to -Vsat . Now the capacitor charges through R towards -Vsat , because the diode become reverse biased. When the capacitor voltage become more negtive than -betaVsat , the comparator switches back to +Vsat , and capacitor C starts charging to +Vsat through R until Vc reaches 0.7V and C become clamped to 0.7V . The pulse width is given by T=RCln(1/1-beta) approximately. If beta=0.5 T=0.69RC . The time period of a trigger must be larger than the output pulse width T. The circuit does not respond to a trigger that appears before the specified output pulsewidth and hence it is called non-retriggerable monoshot .
Components for wiring the circuit
IC 741
D1=D2 = 1N4001
R1 = 10K
R2 =10K
Cd = 0.01μF
R = 15K
Rd = 100K
C = 0.1μF
Vin = 2Vpp

SIMPLE AUTOMATIC STREET LIGHT CIRCUIT

It is the circuit for automatic street light. The main part is a photodiode. And light activated relay. It is nothing but a circuit which operate a relay according to the light input. This circuit set up such a way that the LIGHT will glow until the ligth is incident on the photo diode.
In the absence of light, current into the transistor through the base is sufficient enough to turn the transistor on. This makes the 5V relay operate and the LIGHT gets 230V ac  and it glows. When the light falls on photo diode , its resistance decreases and the current through it increases. This cause the current through the transistor to decrease and the transistor turns off. Then the current through the relay stops and it gets deactivated . In turn , LIGHT turn by the absence of 230V ac.
Componets for wiring this circuit
SL100
R1 = 10K
photo diode
5V relay
lamb
230V ac

LIGHT ACTIVATED RELAY

A light activated relay is nothing but a circuit which operate a relay according to the light input. This circuit set up such a way that the LED will glow until the ligth is incident on the photo diode.
Photo diode is special semiconductor diode operated in reverse biased condition. In no light condition it offer very high resistance. Only current existing in it is the reverse satuaration current due to the minority carriers. When the light falls on it reverse through it will increase.
In the absence of light, current into the transistor through the base is sufficient enough to turn the transistor on. This makes the relay operate and LED circuit gets completed and it glows. When the light falls on photo diode , its resistance decreases and the current through it increases. This cause the current through the transistor to decrease and the transistor turns off. Then the current through the relay stops and it gets deactivated . In turn , LED circuit opens and it glowing.
Components for wiring this circuit
SL100
R1 = 10K
R2 = 100Ω
Relay 5V
photo diode
LED
Vcc = 10V

SCHMITT TRIGGER CIRCUIT USING BC107

The schmitt trigger is an emitter coupled bistable multivibrator with its cross-coupling is removed . It is comparator that is used to convert a periodical random analog wave to square wave having the same frequency of the analog wave. Due to this schmitt trigger is called a squaring circuit.
In this circuit diagram output of this circuit goes high level whan the amplitude of the input goes have above a predetermined level called upper treshold point(utp) output of this circuit goes low level when the amplitude of the input signal goes below a predetermined level called lower treshold point (ltp). The schmitt trigger compares the input analog wave form  with respect to the preset values of UTP and LTP . So it is known as two level comparator.
Without any input signal , transistor Q1 stays in state and Q2 in saturation state. Current Ie2 flows trougth the common emmiter resistor Re causing a potential drop equal to Ie2Re. This point called UTP. When the input amplitude increase and reaches UTP Q1 turns ON. Subsequently Q2 turns OFF and the output raises to Vcc. Now current Ie2 become zero and Ie2 starts flowing through Re. The minimum voltage required to hold the transistor Q1 ON is equal to Vbe cut in + Ie1Re1. When the amplitude of the input sinwave become lessthan this, Q1 turns off, in turns Q2 turns on and the output voltage drops. The value of the input voltage at which transistor Q2 turns on is called LTP. 
components for wiring this circuit
Q1 = Q2= BC107
Rb = 47K
Rc1 = 4.7K
Rc2 = 1.5K
R1 = 10K
R2 = 33K
Re = 3.3K
C1 = 4.7pF
Vin = 20Vpp
Vcc = 8V
Vo= output

SELECTIVE FILTER CIRCUIT

Filters are networks designed to pass only certain desired frequency band. It can be broadly classified as passive or active filtes according to the device used to implement them. High pass and low pass filters are there.
It is a combination of low pass and high pass filtes. For the selection of particular frequency. Low pass filter passes low frequency readily and attenuates high frequencies. High pass filtes passes high frequency and attenuate low frequencies.
     
This circuit is designed by the equation f=1/2 pi RC .
f= input signal frequency.
Low pass filter passes a frequency less than f1 and high pass filtes passes frequency greater than f2.  R1, C1 is for low pass and R2, C2 for high pass. By selection  frequency in between two frequency application, high frequency taken as f1 and low frequency taken as f2. And finding the different values C1 for f1 and C2 for f2. And design the circuit like this.   Input is 5Vpp.
R1=6.8K
R2=6.8K

Jones chopper

Jones chopper is an example of class D commutation in which a charged capacitor is switched by an auxilary SCR to commutate the main SCR. In this circuit SCR1 is the main switch and SCR2 is the auxilary switch which is of lower capacity than SCR1 and is used to commutate SCR1 by a reverse voltage developed across the capacitor C. "The special feature of the circuit is the tapped autotransformer T through a portion of which the load current flows".
Working   
        When T1 is ON, capacitor C discharges resonantly through T1, L1, D1 . This discharge current doesnot flow through L2 and back to the battery because of transformer action of T. The load current is picked up by T1 and the freewheel diode D1 is reverse biased. As the capacitor voltage swings negative, the reverse bias on diode D2 decreases.  This continues upto a time  pi(L1C)^1/2.
            When T2 is on the negative voltage on capacitar C is applied across T1 and it becomes OFF.The load current which is normally constant starts to flow in T2 and capacitor C. The capacitor C charged positively at first upto a voltage equal to supply voltage Vdc.The freewheel diode become forward bias and begins to pickup load current. And capacitor current starts to reduce. After this the energy 1/2LI^2 is the inductance L2 is forced in to the capacitor C.Charging is positively to 1/2CV^2  the capacitor current continues to decrease as a result current through T2 decreases gradually become OFF. The cycle repeat when T1 is again turned ON.
Advantage
The main advantage of JONES chopper over other  the circuit is that
* It allows the use of higher voltage and lower microfarad commutating capacitor. This is because the trapped energy of inductor L2 can be forced in to the commutating capacitor rather than simply charging the capacitor by supply voltage.
* In this circuit there is no starting problem and anyone of the SCR can be turned on initialy there is great flexibility in condrol also.

MONOSTABLE MULTIVIBRATOR USING BC107

Monostable multivibrator also called monoshot, has only one stable state as its name implies. It has also one quasi-stable state. Monostable multltivibrator are used for generating a pulse of desired time period when a trigger voltage is applied. An external trigger forces this circuit to go to quasi-stable state from its stable state and remain in that state for an amount of time determined by the discharging time of the capacitor. R and C are the timing elements and C1 is the speed up capacitor.
This circuit shows a monostable multivibrator using single bias supply. As soon as the power supply is switche ON, transistor Q1 goes to cut off state ane Q2 goes to saturation state due to regeneraive action. The stable state voltages are Vc1=Vcc, Vc2=Vce(sat)+Vre, Vb2=Vbe(sat)+Vre and Vb1<Vbe(cutin)+Vre . 
The moment a negative trigger is applied at the collector of the transistor Q1, transistor Q2 goes to the cut off state resulting Vc2 jumps to Vcc. This sudden rising of the voltgae gets coupled to the base of the transistor Q1 through the commutating capacitor C1 because capacitor acts as a short circuit for instantaneous change of voltage. Therefore, the transistor Q1 goes to ON state. The collector voltage of the transistor Q1 suddenly drops by an amount Ic1Rc1, where Ic1 is the current though the resistance Rc1.
The base voltage of Q2 suddenly drops by an equal amount. Now the  polarity of the voltage across the capacitor C is such a wax that the negative is at its rigit side. Now it charges from this negative potential to +Vcc through R and Q1. When the potential at the right side of the capacitor reaches the cut in voltages, Q2 turns ON. Due to the surge of base current, a momentary overshoot of voltgae occurs, but soon it settles at satuaration voltage+Vbe(sat). Thus the circuit comes back to the stable state. It will continue till the next trigger comes at the collector of Q1. The time duration of the quasi-stable state is given by the expression T=0.69RC.
Components for wiring this circuit
Q1=Q2= BC107
R1 = 47K
R2 = 56K
Rd = 6.8K
Rc1 = 4.7K
Rc2 = 4.7K
R = 100K
Re = 1K
Cd = 0.01μF
C1 = 4.7pF
D = 1N4001
Vcc = 12V
trigger - squre waves
Vc1, Vc2 are outputs

BISTABLE MULTIVIBRATOR USING BC107

Bistable multivibrator circuit is nothing but a cross coupling of two transistor switches. It has two stable states. An external higher switches this circuit from one stable state to the other. Another trigger is needed to switch this circuit back to the old state. Bistable multivibrator is also called a flip-flop or binary circuit. It is nothing but two inverters connectde back to back.
It is the circuit bistable multivibrator using single bias supply. As soon as the circuit is powerf, one transistor goes to OFF state and other to ON state due to the imbalance of circuit parameters. Both the transistors cannot remain in the same state at same time. The collector voltage of the ON transistor will be (Vce)sat +Vre and base voltage will be (Vbe)sat + Vre.
Reverse will be the case for the other transistor. The collector voltage of the OFF transistor will be Vcc. Its base voltage is a samll positive voltgae but less than the voltage at its emitter, to keep it indeed in OFF state.
Suppose transistor Q1 is turned ON and transistor Q2 is turned OFF as soon as the Vcc supply is switche ON. When a negative going trigger appears at the collector of the transistor Q2, it goes to ON state.
Due to the regenerative action, transistor Q1 goes to OFF state. The bistable multivibrator will continue to remain in this state until  a negative going trigger appears at the colletor of Q1.
A speed up capacitor is connected in parallel with the resistor R2 to couple the transition of the voltage at the collector of one transistor to the base of the other transistor.
Components for wiring thia circuit
Q1=Q2= BC107
D1=D2= 1N4001
Rc1=Rc2= 4.7K
R2 = 39K
R1 = 18K
Re = 470Ω
C1 = 4.7pF
C = 220pF
Vcc = 10V
trigger- square waves
Vc1,Vc2 are outputs

Wein bridge oscillator using JFET

The wein bridge osillator employs as balanced wein bridge as the feedback network. Two stage common source amplifier provide 360 degree phase shift to the signal.
  The attenuation of the bridge is calculated to be 1/3 at resonant frequency. There for the amplifirer stage should provide a gain of 3 to.make loop gain unity. Gain preferred to slightly greater than 3 to compensate for the losses occuring in the circuit. Since gain of two stage amplifier is the product of individual stages, over all gain may become very high.
components for wiring the circuit
J1=J2= BFW10
Rd1 - 2.2K
Rd2 - 2.2K
Rs1 - 1K
Rs2 - 1.2K
Rg - 1M
R - 1.5k
Cc1 - 10F
Cc2 - 10F
C - 0.01F
Vdd - +12V

Oscillators

An oscilletor is an electronic device which convert dc power from the supply into ac power in the load. An oscillator generates a signal with out any external input. These are classified in different ways.
According to the principle involved: the oscillations can occur either through +ve feed back mechanism or negative resistance effect.
According to the type of wave form produce: oscillator can generate either sinwave as output or any waveform other than sinusoidal.
According to the feed back circuit: The feed back circuit may contain resistors or capacitors or may contain inductors or capacitors for frequency varietion.
According to the frequency of output signal: the oscillation can be audio frequency AF oscillator (upto 20Kz) or radio frequency oscillators (upto 300MHz) or ultra high frequency UHF oscillators (upto 3GHz) or microwave oscillators (above 3GHz).

Frequency response of an Amplifier

It is a high pass RC circuit. Frequency response indicates the variation of gain of an amplifier for different signal frequencies. Usually , an amplifier can't respond uniformly for all freqencies. Depending on the type of the amplifier the variation differs. In general, the performance of an amplifier remains uniform for mid frequencies. This is because coupling capacitors , bipass capacitors and junction capacitors have negligible effect at mid frequencies. At, low frequencies, the gain of the amplifier is limited by coupling capacitors and emitter by pass capacitors whereas at high frequencies, it is limitted by junction capacitance ot the transistor.
  In general, the low frequency response of an amplifier is governed by the high pass circuit.
Specifications
Vi - input voltage
Vo - output voltage
C - capacitor
R - resistor

simple electronic choke test

                    The 4 tube holder wires are short circuiting as per the circuit diagram. Do not inter change the holder wires. After that one of the supply wire is connected with one point of lamp holder (230/60V ) . And remaining lamp wire and supply wire of choke are connected to the 230V supply.
               If the 230/60V bulb is glow the choke is in working condition , otherwise it is complient.

Principle of chopper circuit

It is a simple chopper circuit.
In this manner, a chopped load voltage is obtained from a constant dc supply of magnitude Vs . In this chopper is represted by a switch SW inside dotted rectangle, which may be turned-on or turned-off as desired. For the sake of highlighting the principle of choper operation The circuitry used for controlling the on,off periods of this switch is not shown. During the period Ton, chopper is on and load voltage is equal to source voltage Vs. During the interval Toff, chopper is off, load current flows through the freewheeling diode FD. As a result, load terminals are short circuited by FD and load voltage is therefore zero during Toff. In this manner, a chopper dc voltage is produced at the load terminals. The load current is continuous. During Ton, load current rises whereas durin Toff load current decays.
The load voltage controlled by varying duty cycle.