1. by using a voltage-controlled current source


The most electronic circuit is assumed to
operate some supply voltage that is usually expected to be constant. The voltage
regulator is the electronic circuit which maintains a constant output voltage
irrespective of change in load current or line voltage

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Background Study

2.1  Applications
of DC-DC Converters

DC Converters can be used in regenerating the braking of dc
motors, thereby returning the energy back into the supply and resulting in energy
savings for the transportation systems that have very regular stops, such as; Trolley
cars, Forklifts trucks, my Haulers and
many more. The DC voltage regulator can also be used in conjunction with an inductor
to generate the dc current source for the current source inverter.  

Linear Regulator

The linear regulator (Shown in Fig.2) is the basic circuit background
for nearly every power supply used in electronics, and is also sometimes known
as a series regulator because of its control on elements are arranged in series
between the input and output. It is a very straightforward regulator to use and
very inexpensive. It operates by using a voltage-controlled current source to power
the fixed voltage to appear as the regulator output. The control circuit board
helps to monitor the output voltage, and adjust the current source so it holds
the output voltage at the desired value. Most linear regulators have a built-in
compensation which is stable with
external components to help control the output voltage, however, some regulators do require some external components
connected from the output lead to the ground to assure that the regulator is

3.2  Zener
Shunt Regulator

The Zener Shunt Regulator is one of the most common and
simplest forms of the shunt regulator, it
is also very easy to function. Once it has gone over the small minimum current the
Zener diode maintains at an almost constant voltage across its terminals, which
allows the series resistor to drop the voltage from the source across to the Zener diode and load. As it continues to hold
the voltage, any differences shown in the load current will not affect the voltage
across the Zener taking up the current differences required, ensuring an
accurate drop across the series regulator.  


3.3  Transistor


Switching Regulator

The switching regulator (Shown in Fig.5) is a voltage regulator
which uses a switch element instead to transform the input power supply into a pulsed
voltage which is then leveled using some eternal
parts, such as; Capacitors, Inductors, and any other components needed. The power
is supplied from the input into the output by switch on the MOSFET (Shown in
Fig.6) switch until the desired voltage has been reached. Once the output
reaches the programmed value, the switch is turned off, thereby no input power
can be consumed. Experiments show that repeating
this operating at a higher speed makes it
possible to supply a more efficient voltage and with less heat.

4.2  Synchronous
Buck Converter 1

A Synchronous Buck Converter is the modified version of the basic
buck converter circuit. The Buck converter (Shown in Fig.7) also known as the
Step-Down Converter is widely used in circuits that step down the voltage levels
from the input voltage, thereby it down converts a DC voltage to a lower DC voltage
of the same division. It uses a transistor as the switch which then alternately
connect and disconnects the input voltage to an inductor.

When the switch is on the input voltage is connected to the
inductor, the change between the input and output voltage is then forced across
the inductor which then causes the current to flow into both the load and
output capacitor as it increases. However, when the switch is turned off the
input voltage that has been applied is then removed, but because the current in
the inductor cannot change instantly, the voltage across the inductor will then
adjust to hold the current at a constant level. This also means a decreasing in
the current flow pushing the input end of the inductor to move negatively till it
reaches the peak where the diode it turned back on, allowing the inductor
current to flow through the load and back through the diode. The capacitor releases
into the load when the switch is off, adding to the total current that has been
supplied to the load.

(Input image here)

In most of the Buck regulator applications, the inductor
current never drops to zero during the full load operation, also known as the continuous
mode operation. The overall performance is better when using the continuous
mode and it also allows a maximum output power to be read from the given input
voltage. Other applications where the maximum load current is quite low can be beneficial towards the discontinuous
mode resulting in a smaller overall converter size. The discontinuous mode
operates at a lower current value, which is stated as harmless because even using
the continuous at a full load can become discontinuous the current decreases.

4.3  Boost
Converter 2

The Boost Converter (Shown in Fig.8) is the opposite of the buck
converter, it is also known as the Step-Up Converter. The regulator takes the
DC input voltage to produce a DC output voltage that is higher than the input.
Much like the buck converter, when the switch is on the input voltage is forced
across the inductor, which thereby causes the current flow through it to
increase. Although when the switch has been turned off, the decreasing inductor
current forces the input end of the inductor to move positively thereby moving
the diodes forwards and allowing the capacitor to charge up to a voltage which is
higher than the input voltage. However, during a steady run, the inductor current
then flows through into both the output capacitor and the load whilst the switch
was off, so when the switch is back on the load current is then supplied only
by the capacitor.   

(input image here)

An important design consideration in the boost regulator is
that the output load current and the switch current are not equal, and the maximum
available load current is always less than the current rating of the switch
transistor. The maximum total power available for conversion in the regulator
is equal to the input voltage multiplied times the maximum average input
current. Since the output voltage of the boost is higher than the input voltage,
the output current must be lower than the input current.


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