Edwin Shankar

Damon Reckley

Ryan Wells

Joe S

Robert C

VOLTAGE REGULATORWITH CONSTANT

CURRENT LIMITING

03/04/2015

Voltage Regulator Theory of Operation

A voltage regulator is a device that maintains a relatively constant output voltage even though its input voltage may be highly variable. There are a variety of specific types of voltage regulators based on the particular method they use to control the voltage in a circuit. In general, a voltage regulator functions by comparing its output voltage to a fixed reference and minimizing this difference with a negative feedback loop.

• It limits current into a circuit.• It lets a circuit maintain a certain voltage• It stabilizes the circuits voltage

Passive RegulatorsPassive voltage regulators are a very simple design that can only be used when the input voltage will always be greater than the output voltage. It contains a resistor that reduces the output voltage to the desired level. The resistor simply dumps the excess voltage as heat. Circuits that may require an increase in voltage will need an active voltage regulator.Basic OperationA basic voltage regulator relies on a simple electromechanical design. A wire connected to the circuit is coiled so that it forms an electromagnet. As the voltage in the circuit increases, so does the strength of the electromagnet. This causes an iron core to move towards the electromagnet which is connected to a power switch. When the moving magnet pulls the switch, it reduces the voltage in the circuit.Negative Feedback LoopThe iron core is held back from the electromagnet by some force, such as a spring or gravity. When the voltage in the circuit decreases, the electromagnet gets weaker. This allows the iron core to move back towards its resting position which turns the switch back on and increases the voltage of the circuit. This produces a negative feedback loop, meaning that the voltage regulator reduces the voltage when it's too high and increases the voltage when it's too low.Increasing SensitivityThe sensitivity of a voltage regulator can be increased substantially with a design that allows the iron core to move along a range of resistances or windings. As the position of the iron core changes, it contacts the circuit at different points, which alters the circuit's voltage as required. This design allows the voltage regulator to respond to very small changes in the circuit's voltage.

Parts List And Specification

• Input Voltage Range: +9V DC TO +15V DC• Q1: 2N3055 Power and Q2: 2N3904 Transistor• D1: 1N4733 Zener Diode• R1=1.0kΩ, R2=10KΩ, R3=10KΩ, R4=1.0 Ω• Nominal Output Voltage: +10V DC• Max Output Current: 500mA

Components Function In The CircuitTransistors:It can amplify and switch electrical power and electronic signals. Transistors are made of semiconductor material with three or more terminals used to connect to an external circuit. By applying a current or a voltage to one of the pairs of the terminals, there is a change in current through another pair of terminals.Diode:Function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be viewed as an electronic version of a check valve.Resistors:The main function of resistors in a circuit is to control the flow of current to other components. Take an LED (light) for example. If too much current flows through an LED it is destroyed. So a resistor is used to limit the current.

Schematic

9v 10v 11v 12v 13v 14v 15v

02468

10121416

VoutVin

Vin/VoutLine Regulation *100%=0.03%/V

150ohm 150ohm 150ohm 150ohm 150ohm

02468

101214

VoutVin

150ohm RL

No load150ohm

220ohm560ohm

750ohm

11.38

11.4

11.42

11.44

11.46

11.48

11.5

11.52

11.54

12Vin

Improvement Of The Voltage Regulator

It appears that Q2 will have to fight with the op-amp output to achieve rollback. Thus stressing both Components. I suggest adding a resistor between the op-amp output and the Q1 base.

Parts