List of Experiments.1. BJT Current Series Feedback.2. Op-Amp Voltage Shunt Feedback.3. Wien Bridge Oscillator with Op-amp.4. Hartley Colpitts Oscillators with Op-amp.5. Square & Triangular Wave Generator with Op-

Amps.6. First Order Band Pass Active Filter.7. Class-AB Push-Pull Power Amplifier.8. Buck Switch mode Power Supply.9. Boost Switch mode Power Supply.

10. Analog to Digital Converter using ADC 0808.11. Digital to Analog Converter DAC 0808.

CURRENT-SERIES FEEDBACK AMPLIFIER

AIM: To measure the voltage gain of current - series feedback amplifier.

CIRCUIT DIAGRAM:

R = 100, RE = 1.5K, RS= RL = 4.7K R1 = 1M (Set Ic = 1ma), CC = 10µF,

CE = 100µF, VCC = 10V, Transistor - BC 547

1. To remove feedback, Short R.

2. By varying R, one can change the feedback.

Procedure

1. Determine the Voltage Gain, Input, Output Impedances and BW,

with and without Feedback. Observe the changes in values.

2. Find the gain at 5 KHz. Multiply it with 0.707. Increase the

frequency till you get the same value. It is f2. Repeat the same till

you get low frequency f1.

Current Shunt Feedback

R = 100, RE = 1.5K, RS = RL = 4.7K, R1 = 1M (Set Ic = 1ma), CC = 10µF, CE

= 100µF, VCC = 10V, Transistors - BC 547

Follow the same procedure as shown above.

Voltage-shunt feedback amplifier (Inverting Amplifier with Feedback).

You cannot find the Gain without Feedback in this case. But you can vary the amount of feedback by changing RF. Ri& Ro cannot be determined.

Voltage Shunt

RF = 47K,RE = 1.5K, RS = RL = 4.7K, R1 = 1M (Set Ic = 1ma)

CC = C = 10µF, CE = 100µF, VCC = 10V

Follow the same procedure as shown above.

Wien- Bridge Oscillator

R1 = R2 = 1.5k, C1 = C2 = 0.1µF, f0 = 1KHz. Ri= 1K, RF = 4.7K Pot.

1. Adjust the Pot till you get a clean Sine Wave.2. For various values of R or C determine the frequency of oscillation.3. The Wien Bridge will produce “Zero” phase shift at only at

resonance frequency determined from above formula. At all other frequencies, a different phase angle which will not satisfy the Barkhausen criteria hence all other frequencies oscillations die down.

The Colpitts oscillator

The Hartley oscillator

Triangular/rectangular wave generator.

R3 = 1K, R1 = 12K, R2 = 180Ω, C = 0.1µF, f = 1KHz.

f=R3

4 R1R2C

A is a comparator. Assume that the comparator output is +Vsat. The voltage at point P = Vsat×(R2/R1). During this time, the integrator output is steadily falling. When the ramp voltage at P equals with Vsat X R2/R1, comparator switches to opposite saturation level.

(R2/R3) = βP/P Vramp = 2VSat× β. The P/P swing of both the waveforms is as shown in fig. Square wave between +Vsat to –Vsat, & Triangular wave is between +βVsat to –βVsat.

P

Sawtooth wave generator:The difference between the triangular and sawtooth waveform is that the rise time of the triangular wave is always equal to its fall time while in sawtooth wave generator, rise time may be much higher than its fall time, or vice versa. The triangular wave generator can be converted into a sawtooth wave generator by injecting a variable dc voltage into the non-inverting terminal of the integrator. This can be done by using a potentiometer as shown in figure. When the wiper of the potentiometer is at the Centre, the output will be a triangular wave since the duty cycle is 50 %. If the wiper moves towards -V, the rise time of the sawtooth becomes longer than the fall time. If the wiper moves towards +V, the fall time becomes more than the rise time.

Procedure:

1. Vary C & find out the frequency.2. Vo1 is Square wave & Vo2 is Sawtooth/Triangular Wave.

P

R3=1K

R1

5 Volt Output Switching Regulator using LM2575

Aim: Design and verify the operation of 5 volt output switching regulator using LM2575.

Apparatus: LM2575, 47 uF, 330 uF, 120 uH, varactor diode ERB81-004, 0-30 v power supply.

The LM2575 series of regulators are monolithic integrated circuits that

provide all the active functions for a stepdown (buck) switching regulator, capable of driving a 1A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V, 15V, and an adjustable output version. Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation and a fixed-frequency oscillator.

The LM2575 series offers a high-efficiency replacement for popular three-terminal linear regulators. It substantially reduces the size of the heat sink, and in many cases no heat sink is required. A standard series of inductors optimized for use with the LM2575 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies.

Other features include a guaranteed ±4% tolerance on output voltage within specified input voltages and output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring 50 μA (typical) standby current. The output switch includes cycle-by-cycle

current limiting, as well as thermal shutdown for full protection under fault conditions.

5V to 12V Boost Converter using LM2577

Aim: Design and verify the operation of 5v to 12v boost converter using LM 2577.

Apparatus: LM2577, IN5822, 220 uF/35v, 0.33 uF, 2.2 K, 100 uH, 18 K, 2K, 1000uF/50v, 0.1 uF, Power supply.

The LM1577/LM2577 are monolithic integrated circuits that provide all of the power and control functions for step-up (boost), flyback, and forward converter switching regulators. The device is available in three different output voltage versions: 12V, 15V, and adjustable. Requiring a minimum number of external components, these regulators are cost effective, and simple to use.

Pin Diagram

Operation

The LM2577 turns its output switch on and off at a frequency of 52 kHz, and this creates energy in the inductor (L). When the NPN switch turns on,

the inductor current charges up at a rate of VIN/L, storing current in the inductor. When the switch turns off, the lower end of the inductor flies above VIN, discharging its current through diode (D) into the output capacitor (COUT) at a rate of (VOUT − VIN)/L. Thus, energy stored in the inductor during the switch on time is transferred to the output during the switch off time. The output voltage is controlled by the amount of energy transferred which, in turn, is controlled by modulating the peak inductor current. This is done by feeding back a portion of the output voltage to the error amp, which amplifies the difference between the feedback voltage and a 1.230V reference. The error amp output voltage is compared to a voltage proportional to the switch current (i.e., inductor current during the switch on time). The comparator terminates the switch on time when the two voltages are equal, thereby controlling the peak switch current to maintain a constant output voltage.

Digital to Analog Converter

Typical DACs are available in either current output (IDAC) or voltage output (VDAC) configurations. While the voltage output VDACs are more convenient to implement, they tend to be slower and more expensive than their current output counterparts (refer to figure 3-1 for a VDAC example). Therefore, for high-speed applications, circuit designers usually choose current output IDACs and then use a high-speed op-amp to provide the I-V conversion at the output of the DAC. For some low cost applications, an IDAC with a simple RC filter on its output is often enough to meet certain non-demanding, high-input impedance applications.

Mathematical analysis of the DAC circuit is as follows:Resolution of the DAC:

1. Number of bits2. Vref

Equation #1: DAC resolution = Vref/( 2n-1)Vref = the DAC reference voltagen = No. of bits (e.g., 8-bit DAC)

Resolution = 5V / 256 = 19.5 mV

This means that the smallest analog voltage step size that can be represented by the DAC with aVref = 5V is 19.5 mV.To determine Vout for any binary value input:

Equation #2: Vout = Vref (N / 2n)

Where: Vout is the DAC’s output voltage(After I–V conversion with an IDAC or the Vout of a VDAC)Vref = the DAC reference voltageN = is the decimal equivalent to the binary input valuen = No. of bits accommodated by the DAC (e.g., 8-bit DAC=256)

If we close the switch for only the LSB (S0 in figure 3-1, binary value = 00000001) we should see approximately 20 mV at the output, because:

5V (1/256) = 19.5 mV

With all 8 switches closed (i.e., binary value = 11111111) we should see approximately5V (255 / 256) = 4.98V at the output (this is illustrated in figure)

Result:

Review Questions:

1) What is the name for this type of DAC?

2) The output voltage is the ---------- sum of all the input voltages in this circuit.

3) List the other types of DAC’s that are available?

Analog to Digital Converter

Aim: To design and verify Analog to digital converter operation

Apparatus: ADC 0808, LED’s, Function generator, connecting wires

Theory: The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding A, B and C address lines.

1. The input control signals OE, PIN-9 and VREF PIN-12 are tied to Vcc PIN-11(+5 volts).

2. Start Conversion (SC) - PIN-6, & End of conversion (EOC) - PIN-7 are shorted to have continuous conversion.

3. 0 to +5V can be applied to PIN-26. For each value of input voltage, note down the 8 digital output (LED's) in tabular form.

4. Pin-10 is clock input (Max.550KHz). Observe the effect of clock. If no clock, no conversion and output will not vary with change in the input voltage. If low frequency is applied say 10Hz, conversion time increases and output (LED's) changes very slowly. So put sufficient higher frequency say 1KHz.

The maximum level of analogue input voltage should be appropriately scaled down below positive reference (+5V) level. The ADC 0808 IC requires clock signal of typically 550 kHz, which can be easily derived from an astable multivibrator, constructed using 7404 inverter gates.

In order to visualize the digital output, the row of eight LEDs (LED1 through LED8) have been used, wherein each LED is connected to respective data lines D0 through D7. Since ADC works in the continuous mode, it displays digital output as soon as analogue input is applied. The decimal equivalent digital output value D for a given analogue input voltage Vin can be calculated from the relationship.