A.2-Constant Current and Constant Voltage Regulator

8/11/2019 A.2-Constant Current and Constant Voltage Regulator

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CONSTANT CURRENT AND CONSTANT

VOLTAGE REGULATOR

GUIDE NAME:

D.RAMYA BY

SRAVANTHI (07241A0219)UJWALA (07241A0222)

SUSHEELA (08245A0201)


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INTRODUCTION

o CONSTANT VOLTAGE REGULATOR

o CONSTANT CURRENT REGULATOR


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INTRODUCTION

CONSTANT CURRENT:

Constant current is a term most often used in

electronics to describe a system that can vary the

voltage across an electronic circuit to maintain a

constant electric current.

An important usage of constant current power supplies

are LEDs, Fluorescent lamps that have very dynamic

electrical resistance and optimally must be operated

within a short range of currents.


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The circuitry which provides a constant current output is

called a constant current regulator or just CURRENT

REGULATOR.

The variable resistor shown on the schematic is used to

illustrate the concept of current regulation.


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In this case the variable resistor (RV) compensates for changes in

the load or dc input voltage. Adequate current regulation results in

the loss of voltage regulation.

Any increase in load resistance causes a drop in current.To maintain a constant current flow, the resistance of RVmust be reduced whenever the load resistance increases.

This causes the total resistance to remain constant.


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CONSTANT VOLTAGE REGULATOR:

A voltage regulator is an electrical regulating device that is

made to automatically sustain a constant level.

Voltage regulators vary in design. Some use passive or active

components, while others use electromechanical mechanisms.

The voltage regulator is designed to maintain a constantvoltage level.

7812,7912 constant regulators

LM137 variable regulator


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Regulator with an operational amplifier:

The zener diode Vz acts as a voltage reference for the circuit,

and is fed into the non-inverting input of the operational

amplifier. The voltage divider formed by R1 and RF sets the

voltage level of the inverting input of the op amp, which is

basically a feedback from the circuit output to the op

amp. The NPN transistor is used to boost the output current of

the circuit.


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The voltage at the non-inverting input of the op amp is at the

zener voltage, while the voltage at the inverting input is

always a fraction of the output voltage as defined by RF and

R1.

When the output exceeds the set level, the inverting input

voltage exceeds that of the non-inverting input, causing the

output of the op-amp to go 'low'. This turns off the NPNtransistor, causing the output voltage to dip.

When the output goes below the set level, the reverse

happens, i.e., the op-amp's output goes 'high', causing the NPNtransistor to turn on and pull the voltage up.


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BLOCK DIAGRAM


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OP-AMP LM124


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CHARACTERISTICS OF AN IDEAL OP-AMP

Voltage gain, input impedance and band width are infinity.

Output impedance is zero.

When equal voltage are applied at the two input terminals, theoutput is zero.

There is no change in the characteristics features, with changes

of temperature


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CIRCUIT DIAGRAM


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CIRCUIT DESCRIPTION

The circuit shown in the above figure is CCCV regulator. It works from source

voltage of 20V to 35V. It provides constant current(settable below 500mA) and

constant voltage output (settable below 15V). The CC value is settable by the POT

R12. The CV value is settable by POT R3. The main power device M1 is a p

channel MOSFET. The current feedback is through R17. The voltage feedback is

through R21 and R22. the housekeeping power is from zener D1 biased with the

resistor R1.Current signal is amplified with U2C (gain of 10).U1B is the current

controller working as PI amplifier(proportional integrator)amplifier.R3 sets the

voltage reference (full pot setting 15V). The voltage controller output is attenuated

through R9 and R13 and serves as the current reference. R12 sets the current limit

(full pot setting 0.5A).

Current feedback:

iR

RiIfeedback 75.1

19

20


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Current reference is variable from 0 to 04.75V (saturation level of U1A through R9,R13

and R12. the corresponding current limit is variable between 0 and 650mA).

voltage feedback:

Voltage references is variable from 0 to 5V (zener D1 voltage through R2,R3 and R4. the

corresponding set is variable between 0 to 15V)

32221

22 outoutfeedback

V

RR

RVV


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SIMULATION CIRCUIT


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SIMULATION WAVEFORMS


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TIME INPUTVOLTAGE OUTPUT

VOLTAGE

OUTPUT

CURRENT

2ms 20V 15V 0.75A

4ms 30V 15V 0.75A

6ms 35V 15V 0.75A


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LIST OF MAJOR COMPONENTS

S.NO NAME OF THE

COMPONENT

SYMBOL SPECIFICATION

1. LINEAR IC U1A LM124

2. MOSFET M1 IRFZ44N,2A,

40V, P channel

3. TRANSISTOR Q1 2222A


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ADVANTAGES

OF LM124

Eliminates need for dual supplies

Four internally compensated op amps in a single

package Compatible with all forms of logic

Power drain suitable for battery operation

APPLICATIONS


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APPLICATIONS:

Constant current and constant voltage:

In adapters

battery chargers

pannel lighting

used in SMPS


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HARDWARE RESULTS


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20V INPUT


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25V INPUT


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30V INPUT


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THANK YOU

A.2-Constant Current and Constant Voltage Regulator

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