GOVERNMENT ENGINEERING

COLLEGE MODASA

Group - 19

SUBJECT: ANALOG ELECTRONICS

SUBMITTED BY:

SWETA RAJPUT

KUNJ PATEL

GUIDED BY:

PROF. M.N PRIYADARSHI

CERTIFICATE This is to certify that group……………………. Of rollno……............ and ……………… of electrical department has satisfactorily completed the course in ……………………………………………………….

Within four walls of Govt. Engg College Modasa year 2013-14.

Submission date………....

Sign of professor………..

V-I CONVERTER

Abstract:

In this project a study of a voltage to current converter (VtoI) is given. A conventional VtoI converter converts input voltage into an appropriate current with the use of op-amp ic 741. On the basis of connection of resistors, there are two types of VtoI converters the one with floating load and the other with grounded load. In which we are going to study a floating load VtoI converter. The construction of a floating load V2I converter is same as a non-inverting amplifier. A simple and low cost V2I converter design and its performance analysis is the main objective of this thesis.

Name/abbreviations:

V= voltage

I= current

L=load

In = input

O = output

Vid = difference between two voltages

List of figures:

2 figures

6 picture

2 simulations.

Content:

Title page: Certificate: Abstract:

Abbreviations: List of figures: Chapter 1:

Introduction and survey Chapter 2: Basic theory Chapter 3:

Simulations

Chapter 4:

Hardware implementation

Chapter 5:

Conclusion and future work

INTRODUCTION AND SURVERY

V-I converter is a device which uses IC 741(op/-amp) to convert voltage into current. There are basically two types of v-I converter

(I)V-I converter with floating load

(II)V-I converter with grounded load

Basic relation of v-i converter is output voltage is equal to supplied voltage divided by resistance. The circuit of floating load is similar to the circuit of non-inverting op-amp and the circuit of grounded load is a bit complicated which is explained later.

The reference of the project and the theory of the report has been referred from the reference book “Op-amp and linear integrated circuits” by Shri Ramakand A. Gayakward, Page number 223 to 227.

BASIC THEORY

Voltage to current (V-I) converters:

V-I converter is a device which uses IC 741(op/-amp) to convert voltage into current. There are basically two types of v-I converter

(I)V-I converter with floating load

(II)V-I converter with grounded load

(I) VOLTAGE TO CURRENT CONVERTER

WITH FLOATING LOAD: Figure 1 shows a voltage to current converter in which load resistor RL is floating (not connected to ground). The input voltage is applied to the non-inverting input terminal, and the feedback voltage across R1 drives the inverting input terminal. This circuit is also called a current series negative feedback amplifier because the feedbac voltage across R1 (applied to the inverting terminal) depends on the output current Io and is in series with the input difference voltage Vid. Writing Kirchoff’s voltage for the input loop, Vin= Vid + Vf

But Vid is almost equal to 0, since A is very large ; therefore,

Vin = Vf

Vin = R1io Or Io = vin/R1

This means that in the circuit of figure 1 an input voltage Vin is converted into an output current of Vin/ R1. In other words, input voltage Vin appears across R1. If R1 is a precision resistor, the output current (io = Vin/R1) will be precisely fixed.

The voltage to current converter can be used in such applications as low voltage dc and ac voltmeters, diode match finders, light-emitting diodes (LEDS), and zener diode testers.

FIGURE:“Voltage to current converter with floating load.”

VOLTAGE-TO-CURRENT CONVERTER WITH GROUNDED LOAD:

Another version of the voltage-to-current converter is shown n figure 2. In this circuit, one terminal of the terminal of the load is grounded, and load current is controlled by an input voltage. The analysis of the circuit is accomplished by first determining the voltage V1 at the non inverting input terminal and then establishing the relationship between v1 and the load current.

Writing kirchoffs current equation at node V1.

I1 +I2 = IL

Vin – V1/R + Vo – V1/R = IL

Vin + Vo – 2V1 = IL

Therefore,

V1= Vin + Vo – ILR/2

Since the op-amp is connected in the non inverting mode, the gain of the circuit in figure 2 is 1+ R/R = 2. Then the output voltage is

Vo = 2V1

= Vin + Vo – ILR

That is,

Vin = ILR

IL = Vin/R

This means that the load current depends on the input voltage Vin and resistor R. Notice that all resistor must be equal in value.

The voltage – to – current converter of figure may be also be used in testing such devices as zenners and LEDS forming a ground load. However the circuit will perform satisfactorily provided that load size greater than or equal to R value.

FIGURE:

“Voltage to current converter with grounded load.”

SIMULATION OF CIRCUIT:

V to I converter with floating load:

HARDWARE IMPLEMENTATION:

V TO I CONVERTER WITH FLOATING LOAD:

Input voltage Output current

CONCLUSION AND FUTURE WORK: The basic idea behind the circuit containing op-amp compensates the external losses caused by the load adding

as much voltage to the input voltage source as it loses across the load.

In the circuit of an op amp voltage to current converters the op amp adds much voltage to the voltage of the input source as it losses across the external load. The op amp compensates the local losses caused by this external load (conversely, in the opposite op amp inverting current to voltage converter, the op amp compensates the losses caused by the internal resistor).

“APPLICATIONS OF V TO I CONVERTERS:”

Once we created a perfect v to I converter we may use it as a building block to build more complex compound circuits.

For this purpose, we have only to connect consecutively the separate building blocks.

Examples

Op amp RL integrator = op-amp V to I converter + I to V C integrator

Op amp RL differentiator = op amp V to I converter +I to v L differentiator

Etc....