• Author / Uploaded
• Rahul Agarwal

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CHAPTER 1 INTRODUCTION A digital thermometer is used to measure the atmospheric temperature.EThe

digital

-thermometer can measure temperatures up to 150°C with an accuracy of ±1°C.1 The temperature is read on a 1V full scale-deflection (FSD) moving-coil voltmeter or digital voltmeter. Operational amplifier IC 741 (IC3) provides a constant flow of current through the base-emitter junction of npn transistor BC108 (T1). The voltage across the base-emitter junction of the transistor is proportional to its temperature. The transistor used this way makes a low-cost sensor. You can use silicon diode instead of transistor. The small variation in voltage across the base-emitter junction is amplified by second operational amplifier (IC4), before the temperature is displayed on the meter. Preset VR1 is used to set the zero-reading on the meter and preset VR2 is used to set the range of temperature measurement. Operational amplifiers IC3 and IC4 operate off regulated ±5V power supply, which is derived from 3terminal positive voltage regulator IC 7805 (IC1) and negative low-dropout regulator IC 7660 (IC2). The entire circuit works off a 9V battery. Assemble the circuit on a general-purpose PCB and enclose in a small plastic box. Calibrate the thermometer using presets VR1 and VR2. After calibration, keep the box in the vicinity of the object whose temperature is to be measured. Operational amplifier IC 741 (IC3) provides a constant flow of current through the base-emitter junction of NPN transistor BC108 (T1). The voltage across the base-emitter junction of the transistor is proportional to its temperature. The transistor used this way makes a low-cost sensor. we can use silicon diode instead of transistor. The small variation in voltage across the base-emitter junction is amplified by second operational amplifier (IC4), before the temperature is displayed on the meter. Preset VR1 is used to set the zero-reading on the meter and preset VR2 is used to set the range of temperature measurement. Operational amplifiers IC3 and IC4 operate off regulated +_5V power supply, which is derived from 3-terminal positive voltage regulator IC 7805 (IC1) and negative low-dropout regulator

IC

7660

(IC2).

The

entire 1

circuit

works

off

a

9V

battery.

Assemble the circuit on a general-purpose PCB and enclose in a small plastic box. Calibrate the thermometer using presets VR1 and VR2. After calibration, keep the box in the vicinity of the object whose temperature is to be measured.

1.1 Circuit Diagram:-

Figure 1.1:- Project Circuit Diagram

2

1.2 Component list:-

Component

Value

Quantity

R1

100 ohm

1

R2,R3

10 K ohm

1,1

VR1

100K ohm

1

VR2

500k

1

C1

220nf

1

C2,C3

10µf

1,11

C4

1µf

1

IC1,IC2

741

2

IC 3

7660

1

IC 4

7805

1

Resistance

Capacitors

IC’S

Table 1.1:- Table of Components Required

CHAPTER 2 3

IC-7805

The MC78XX/LM78XX/MC78XXA series of three terminal positive regulators are available in the TO-220/D-PAK package and with several fixed output voltages, making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to .Obtain adjustable voltages and currents.

2.1 Pin Diagram:-

Figure2.1:- Pin diagram of 7805 IC

2.2 Data Sheet:4

Table 2.1:- Data Sheet of IC 7805

2.3 Note:Load and line regulation are specified at constant junction temperature. Changes in Vo due to heating effects must be taken into account separately. Pulse testing with low duty is used.

2.4 Internal Block Diagram of IC 7805:5

Figure 2.2:-Internal Block Diagram of IC 7805

CHAPTER 3 IC 741 (OPERATIONAL AMPLIFIER) 6

The term operational amplifier or "op-amp" refers to a class of high-gain DC coupled appliers with two inputs and a single output. The modern integrated circuit version is typeset by the famous 741 op-amp. Some of the general characteristics of the IC version are: _ High gain, on the order of a million _ High input impedance, low output impedance _ Used with split supply, usually +/- 15V _ Used with feedback, with gain determined by the feedback network. The operational amplifier (op-amp) was designed to perform mathematical operations. Although Now superseded by the digital computer, op-amps are a common feature of modern analog electronics. The op-amp is constructed from several transistor stages, which commonly include a differential input Stage, an intermediate-gain stage and a push-pull output stage. The deferential amplifier Consists of a matched pair of bipolar transistors or FETs. The push-pull amplifier transmits a large Current to the load and hence has a small output impedance. The op-amp is a linear amplifier with Vout / Vinp. The DC open-loop voltage gain of a typical op-amp is 103 to 106. The gain is so large that most often feedback is used to obtain a specific transfer function and control the stability. Cheap IC versions of operational appliers are readily available, making their use popular in any analog circuit. The cheap models operate from DC to about 20 kHz, while the high-performance models operate up to 50 MHz. A popular device is the 741 op-amp. It is usually available as an IC in an 8-pin dual, in-line package (DIP).

3.1 Circuit symbol:-

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Figure 3.1:- Circuit symbol and DIP circuit of IC 741

3.2 Inverting and non-inverting amplifier:Basic circuits for inverting and non-inverting amplifier are schematically shown in Fig. 2. The gain of the inverting amplifier is simply given by..

and the gain of the non-inverting amplifier is given by..

8

Figure 3.2:- Circuit for inverting and non-inverting amplifier

3.3 Offset voltage:A practical concern for op-amp performance is voltage offset. That is, effect of having the output voltage something other than zero volts when the two input terminals are shorted together. Remember that operational appliers are deferential appliers above all: they're supposed to amplify the deference in voltage between the two input connections and nothing more. When that input voltage deference is exactly zero volts, we would (ideally) expect to have exactly zero volts present on the output. However, in the real world this rarely happens. Even if the op-amp in question has zero common-mode gain, the output voltage may not be at zero when both inputs are shorted together. This deviation from zero is called offset. A perfect op-amp would output exactly zero volts with both its inputs shorted together and grounded. However, most op-amps of the shelf will drive their outputs to a saturated level, either negative or positive. Offset voltage will tend to introduce slight errors in any op-amp circuit. So how do we compensate for it? There are usually provisions made by the manufacturer to trim the offset of a packaged pomp. Usually, two extra terminals on the op-amp package are reserved for connecting an external potentiometer. These connection points are labeled offset null.

3.4 Input bias current:Inputs on an op-amp have extremely high input impedances. That is, the input currents entering or exiting an op-amp's two input signal connections are extremely small. For most purposes of op-amp circuit analysis, we treat them as though they don't exist at all. We 9

analyze the circuit as though there was absolutely zero current entering or exiting the input connections. This idyllic picture, however, is not entirely true. Op-amps, especially those opamps with bipolar transistor inputs, have to have some amount of current through their input connections in order for their internal circuits to be properly biased. These currents, logically, are called bias currents. Under certain conditions, op-amp bias currents may be problematic. The following circuit illustrates one of those problem conditions: Another way input bias currents may cause trouble is by dropping unwanted voltages across circuit resistances. Take this circuit for example:

Figure 3.3:- Calculation of Bias Current with IC 741

We expect a voltage follower circuit such as the one above to reproduce the input voltage precisely at the output. But what about the resistance in series with the input voltage source? If there is any bias current through the non inverting (+) input at all, it will drop some voltage across Rin, thus making the voltage at the non inverting input unequal to the actual Vin value. Bias currents are usually in the micro amp range, so the voltage drop across Rin won't be very much, unless Rin is very large.

10

3.5 Measurement of input bias current:As mentioned earlier, input bias current is very small in magnitude - so, measuring it directly is not a good idea. However, it can be measured cleverly using the following circuit.

Figure 3.4:- Circuits to measure input bias currents Ib1 and Ib2

Fig. 3.4(a) is just the circuit for an inverting amplifier, with the input grounded. So, the voltage at the inverting input terminal should be ideally zero. But from the circuit above, one can see that the voltage at the inverting input has two contributions - one, Vout reduced by the potential divider made out of Ra and Rb, i.e., Rb Ra+Rb Vout - two, the voltage drop over the R1 if there is a non-zero input bias current owing. Thus, we can write

If Ra = 10 k, Rb = 780 and R1 = 1 M, we get

Input bias current Ib2 can be similarly measured using the circuit in Fig. 3(b), which represents a non-inverting amplifier, with the input grounded through the resistor R2. The voltage at the 11

non-inverting terminal would be Ib2R2, which gets amplified to give Vout. Using the relation for non-inverting gain, one can write

3.6 Op-amp as integrator and differentiator:-

Figure 3.5:- integrator

12

Figure 3.6:-differentiator In the case of an integrator, the output voltage will be

Various kinds of input waves can be given as input. The rectangular wave, for example, will produce the following output:

Figure 3.7:-Output and Input Waveforms of a Integrator 13

CHAPTER 4 IC 7660 (NEGATIVE VOLTAGE REGULATOR IC) The MAX1044 and ICL7660 is monolithic, CMOS switched-capacitor voltage converters that invert, double, divide, or multiply a positive input voltage. They are pin compatible with the industry-standard ICL7660 and LTC1044. Operation is guaranteed from 1.5V to 10V with no external diode over the full temperature range. They deliver 10mA with a 0.5V output drop. The MAX1044 has a BOOST pin that raises the oscillator frequency above the audio band and reduces external capacitor size requirements. The MAX1044/ICL7660 combines low quiescent current and high efficiency. Oscillator control circuitry and four power MOSFET switches are included on-chip. Applications include generating a -5V supply from a +5V logic supply to power analog circuitry. For applications requiring more power, the MAX660 delivers up to 100mA with a voltage drop of less than 0.65V.

4.1 Typical circuit description:-

Figure 4.1:- IC 7660

14

Figure 4.2:-pin configuration of IC 7660

4.2 APPLICATION OF 7660 VOLTAGE REGULATED IC:•

-5V Supply from +5V Logic Supply

•

Personal Communications Equipment

•

Portable Telephones

•

Op-Amp Power Supplies

•

EIA/TIA-232E and EIA/TIA-562 Power Supplies

•

Data-Acquisition Systems

•

Hand-Held Instruments

•

Panel Meters

15

4.3 FEATURES OF IC 7660:•

Miniature μMAX Package

•

1.5V to 10.0V Operating Supply Voltage Range

•

98% Typical Power-Conversion Efficiency

•

Invert, Double, Divide, or Multiply Input Voltages

•

BOOST Pin Increases Switching Frequencies (MAX1044)

•

No-Load Supply Current: 200μA Max at 5V

•

No External Diode Required for Higher-Voltage Operation.

4.4 ORDERING INFORMATION:-

Table 4.1:- Ordering Information of IC 7660

16

4.5 ELECTRICAL CHARACTERISTIC OF IC 7660:-

Table 4.2:- ELECTRICAL CHARACTERISTIC OF IC 7660

17

4.6 PIN DESCRIPTION:-

Table 4.3:- Pin Description of IC 7660

18

CHAPTER 5 ZENER DIODE A zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "zener knee voltage" or "zener voltage." The device was named after Clarence Zener, who discovered this electrical property. Many diodes described as "zener" diodes rely instead on avalanche breakdown as the mechanism. Both types are used. Common applications include providing a reference voltage for voltage regulators, or to protect other semiconductor devices from momentary voltage

Figure 5.1:- Zener diode

19

Figure 5.2:- Output characteristics of zener diode

5.1 Operation of Zener Diode:A conventional solid-state diode will not allow significant current if it is reverse-biased below its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode will be permanently damaged due to overheating. A zener diode exhibits almost the same properties, except the device is specially designed so as to have a greatly reduced breakdown voltage, the so-called zener voltage. By contrast with the conventional device, a reverse-biased zener diode will exhibit a controlled breakdown and allow the current to keep the voltage across the zener diode close to the zener breakdown voltage. For example, a diode with a zener breakdown voltage of 3.2 V will exhibit a voltage drop of very nearly 3.2 V across a wide range of reverse currents. The zener diode is therefore ideal for applications such as the generation of a reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low- applications. Current another mechanism that produces a similar effect is the avalanche effect as in the avalanche diode. The two types of diode are in fact constructed the same way and both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a positive temperature coefficient. In a 5.6 V diode, the two effects occur 20

together and their temperature coefficients nearly cancel each other out, thus the 5.6 V diode is the component of choice in temperature-critical applications. Modern manufacturing techniques have produced devices with voltages lower than 5.6 V with negligible temperature coefficients, but as higher voltage devices are encountered, the temperature coefficient rises dramatically. A 75 V diode has 10 times the coefficient of a 12 V diode. All such diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of "zener diode".

5.2 Construction of Zener Diode:The zener diode's operation depends on the heavy doping of its p-n junction. The depletion region formed in the diode is very thin (