2. 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
3. Passive Regulators
Passive 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 Operation
A 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 Loop
The 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 Sensitivity
The 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.
4. 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
5. Components Function In The Circuit
Transistors:
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 curren
flows through an LED it is destroyed. So a resistor is used to limit the
current.
10. 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.
