Part IINTRODUCTION
1.1 Theories/Concept of the Design
A fixed variable transformer has an input of 220V and steps-down
to a wide variety of fixed AC Voltage, the outputs are 12V, 9V, 6V,
4.5V, and 3V. These voltages are the range needed by some
electronic devices. These ranges will be used to convert AC to DC
Voltage without the aid of voltage drop, potentiometer or any
devices that will alter the voltage to get the desired value.
Through these we could have a fixed variable DC Voltage.The desired
DC output voltages are 12V, 9V and 3V, these outputs are necessary
due to the design are made to supply a parallel set of LED. The
variety of DC Voltage is also been sighted in order to get the
desired amount of luminance in the LED. The luminance of the LED is
directly proportional to the output voltage of the power supply but
inversely proportional to the life span of the LED. So we came up
with the idea that it should be user-choice to manipulate the
output voltage of the power supply.From the transformer, we have a
supply of AC voltage 12V, 9V and 3V and we need 12V, 9V and 3V of
DC Voltage, so therefore the component or circuits needed are
rectifier (to rectify the AC wave), capacitor (to fill-out the
ripples), voltage regulator (to regulate the voltage output). 1.2
Previous Research and Studies
Creating a simple power supply based upon our studies is
possible, but in order to create an industry standard power supply,
we looked for some researches and studies that are probably related
to and connected to our design.These are some ideas that we had
considered to create our design:
Phase-controlled AC to DC power conversion has the disadvantages
of low power factor and harmonic pollution on the utility side,
particularly in the case where DC voltage regulation is required.
This paper presents a one-stage single-phase controlled rectifier
which has a wide output variation on the DC output maintaining
unity power factor and sinusoidal current on the input side. This
scheme also provides galvanic isolation which is required in most
of the industrial applications with a transformer of small size
compared to the ones used with the phase-controlled converters.
Three control strategies for the operation of the converter are
proposed and verified experimentally. The harmonic spectra on the
AC side is analytically derived and its low frequency harmonics up
to half of the switching frequency or higher orders have been
eliminated depending on the control strategies.AC TO DC POWER
CONVERSION WITH UNITY POWER FACTOR AND SINUSOIDAL INPUT
CURRENTGeunhie Rim and R.KrishnanDept. of Electrical EngineeringVPI
& SU. Blacksburg, VA 24061
The aim of this design is to present a theoretical and practical
analysis of one of the most popular AC-DC converter topology. This
topology is used to feed a DC-DC switchmode converter from dual
input voltage operation (230Vrms, 50Hz / 115Vrms, 60 Hz). Simple
expressions are obtained for all RMS and peak currents and
voltages, the mathematical analysis of this multifunctional AC-DC
converter becomes very simple if the suitable assumptions are made.
There is a good agreement between experimental results and the
mathematical analyis predictionsLine Input AC to DC Conversion and
Filter Capacitor Design
J. Doval-Gandoy, C. Castro, C. MartnezDpto. Tecnologia
ElectonicaUniversidad de VigoVigo, [email protected] basic
half-bridge topology provides some implicit problems for designers
who wish to create a high-linearity power converter. The power
stage switches are normally operated in strict time alternation.
The topology has an inherent fault path when both switches are
enabled. Therefore, it is common practice to add a third state to
the switching sequence with all switches off (dead time) to reduce
the probability of common-mode (shootthrough) currents. The
insertion of the dead-time state creates an inherent nonlinearity
in the conversion cycle for output currents near zero current as
the converter does not remain in continuous current mode (CCM). The
effects of a dead zone are additive to the distortion resulting
from switch and freewheel diode losses. When used as amplifiers,
wide-bandwidth dc-to-ac power converters often require relatively
high-switching frequencies to provide ample bandwidth for
processing and filtering a full-band signal. For example, audio
pulse width modulation (PWM) amplifiers can be designed to have
adequate 20- kHz bandwidth and acceptably low-output impedance when
switched at 500 kHz. The higher the operating frequency (shorter
conversion cycle), the larger the proportion of the switching cycle
that is lost by a given dead-time interval. This also increases the
amount of nonlinearity created by the dead zone in the conduction
cycle. A number of partial solutions have been suggested for
improving this problem. A better solution is to develop a topology
that eliminates the shoot hrough high current path and allows the
sum total switch duty cycle to be unity.Precision DC-to-AC Power
Conversion by Optimization of the Output Current WaveformThe Half
Bridge RevisitedGerald R. Stanley, Member, IEEE, and Kenneth M.
Bradshaw, Member, IEEE
Based on what weve researched it is possible to create an
adjustable power supply using a rotary switch that alter the source
and same way changes our output.
1.3 Applicable Standards Part II
Overview
ON Semiconductor was the first Semiconductor company to provide
an 80 PLUS open reference design for an ATX Power Supply in 2005.
This 1st generation reference design, was certified and met all the
requirements of the 80 PLUS program. Following on this successful
1st generation design, ON Semiconductor is introducing its improved
2nd Generation reference design. This 2nd generation design
utilizes newer ICs from ON Semiconductor that enable this design to
exceed 80% efficiency starting at 20% load across different line
conditions with ample margin to spare.This reference document
provides the details behind this 2nd generation design. The design
manual provides a detailed view of the performance achieved with
this design in terms of efficiency, performance, thermals and other
key parameters. In addition, a detailed list of the
bill-of-materials (BOM) is also provided. ON Semiconductor will
also be able to provide technical support to help our customers
design and manufacture a similar ATX power supply customized to
meet their specific requirements. The results achieved in this 2nd
generation design were possible due to the use of advanced new
components from ON Semiconductor. These new ICs not only speeded up
the overall development cycle for this new design, but also helped
achieve the high efficiencies while at the same time keeping a
check on the overall cost. With the use of these new ICs, ON
Semiconductor has proven again that the emerging requirements for
high efficiency desktop power supplies can be met and further, can
be optimized to meet specific performance vs. cost goals. This 2nd
generation design consists of a single PCB designed to fit into the
standard ATX enclosure along with a fan. Figure 1 below presents
the overall architecture employed in this design detailed
schematics are included later in this design manual. As seen in
figure 1, this design employed an Active Clamp forward topology
using the new, highly integrated Active Clamp Controller IC from ON
Semiconductor NCP1562. A Continuous Conduction Mode (CCM) Power
Factor Correction (PFC) IC was employed for the active PFC circuit.
This IC, the NCP1653 provides an integrated, robust and
costeffective PFC solution. The standby controller, NCP1027, is an
optimized IC for the ATX power supply and incorporates a
high-voltage MOSFET. On the secondary side, this architecture
employs a post regulator approach for generating the 3.3 V output.
This is an alternative approach to the traditional magnetic
amplifier (Mag Amp) approach. Though ON Semiconductor believes that
this post regulator approach provides the highest efficiency
amongst the different means of generating these outputs in the
power supply, it is important to note that if the customer desires
to use a different approach, that is possible i.e. a similar design
can be developed that utilizes all the other pieces of this
architecture without the post regulator and still achieve very good
results.With the introduction of this 2nd generation,
high-efficiency ATX Power Supply, ON Semiconductor has shown that
with judicious choice of design tradeoffs, optimum performance is
achieved at minimum cost.
Figure 1: Reference Design Architecture Block
DiagramSpecifications The design closely follows the ATX12V version
2.2 power supply guidelines and specifications available from
www.formfactors.org, unless otherwise noted. For instance, our
reference design had a target of +/- 5% tolerance for both the 5 V
and 5 Vstandby outputs. Further, the efficiency targets for the 80
PLUS program and the EPAs Energy Star specification Energy Star
Program Requirements for Computers, version 4.0 that is set to take
effect from July 20, 2007 were targeted. Key specifications are
included in Table 1 below.
Table 1: Target SpecificationsTarget specifications for other
key parameters of the reference design include:- Efficiency:
Minimum efficiency of 80% for 20%, 50% and 100% of rated output
load conditions as defined by the 80 PLUS requirements as well as
the Energy Star specification. - Power Factor: Power factor of 0.9
or greater at 100 % load. - Input Voltage: Universal Mains 90 Vac
to 265 Vac, 47 63 M Hz. - Output Power: Total maximum output power
is 305 W. - Safety Features: As per the ATX12V specification, this
design includes safety features such as OVP, UVP, and OCP. - This
design meets the IEC1000-3-2 requirements over the input line range
and under full load conditions. - This converter was designed for a
20 ms minimum Hold-up time.- Physical dimensions: This converter is
designed to fit into the standard ATX enclosure with dimensions of
150 mm x 140 mm x 86 mm.Architecture OverviewBefore discussing the
power supply architecture of the Generation 2 design, it is worth
reiterating the design goals. We are tasked with providing a
flexible power platform, which is required to have the lowest cost
and highest efficiency that can be packaged in a small volume. The
architecture must deliver a minimum of 80% efficiency over a wide
range of operating conditions (high-line and low-line) as well as
rated output load conditions (20% load and above). In addition we
require a robust design solution having low parts count to provide
the same performance on a unit to unit basis in a high volume
manufacturing environment. The architecture selected follows a
traditional two stage conversion approach as illustrated in Figure
1. It is worth noting that in order to achieve 80% efficiency
overall, the efficiency of each of the two conversion stages must
exceed 90 %. The front-end is a universal input, active power
factor boost stage delivering a constant output voltage of 385 V to
the active clamp stage. The second stage consists of two, dc-dc
converters. The first down-stream converter processes 290 W
required by the system in the form of tightly regulated +/-12 V, +5
V and +3.3 V outputs. The second converter delivers 15 W of standby
power to another isolated 5 V rail. ON Semiconductor has developed
multiple power management controllers and MOSFET devices in support
of the ATX program. Web based data sheets, design tools and
technical resources are available to assist design optimization.
The ICs, supporting the ATX Generation 2 platform, are the NCP1653
PFC controller, the NCP1562 active clamp controller, the NCP4330
post regulator, the NCP1027 standby controller, and the NTP48xx
family of MOSFET synchronous rectifiers. It is not possible to
discuss the tradeoffs involved in each conversion stage at length,
but the selection of the active 9 clamp forward converter topology
is a key one and will be covered in depth. Each controller is
highly integrated and offers the lowest external parts count
available.
Part IIDESIGN SPECIFICATION
2.1 Design Simulation Lay-out
Rectifier (3N246)
Voltage Regulator (MC7815CT)AC Input
DC Output
Capacitor
ItemValueQuantity
Rectifier3N2461
Capacitor100F1
RegulatorMC7815CT1
2.2 Block Diagram
TransformerInputAC Voltage
Bridge Rectifier
Smoothing Capacitor
OutputDC VoltageVoltage Regulator
The design is composed of many steps; transformer, step down the
level of AC current from the wall current. Full-wave bridge
type-rectifier provides a full-wave rectified voltage. Capacitor
Filters, produce a DC Voltage supply but it still has some ripples
voltages. IC Regulator, removes and varies the voltage output.2.3
Schematic Diagram
2.4 Circuit Description and Operation
Firstly let us discuss about the need for the smoothing
capacitance. As you know the output of the bridge rectifier will be
as follows
Output of Brige Rectifier
As you can see, although the waveform can be considered to be a
DC voltage since the output polarity does not invert itself, the
large ripples that exist in the output makes sit almost impossible
to be used in any powering applications. So it is to remove these
ripples that the smoothing capacitor is used. Now the output after
thecapacitorwill be
Output of Capacitor FilterNow all we need to know is the value
of Vr which can be selected according to our need. Normally we take
it as 0.4V which means that the maximum size of ripples in the
output waveform will be 0.4v. One dis advantage of thismethod is
that the ripple factor depends in output current, ie. the ripples
may become larger or smaller while we vary the load. This is the
reason why it is absolutely necessary for the capacitor to be
followed by a voltage regulator IC.The most important part of this
circuit is the MC7815CT variable voltage regulator. The MC7815CT is
amonolithic integrated circuit with adjustable
3-terminalpositive-voltage regulator designed to supply morethan
1.5 A of load current with an output voltage adjustableover a 1.2 V
to 37 V range. It also comes with internal currentlimiting, thermal
shutdown, and safe areacompensation. All this makes it a very good
candidate for a regulator if we need a moderately accurate supply
with medium power output. For more details you may refer its data
sheet. As you can see it has three pins, INPUT This is where we
give the unregulated input OUTPUT This is where we will get the
regulated output ADJUST The variable resistor connected to this
pin, controls the output voltage
AC TO DC POWER CONVERSION
By
Amparo, Veenee GraceCezar, SeanImam, MohamadRodriguez,
YvenRosero, LeomerPlacidas, Sarah
A Project Report Submitted to the Electronics Engineering
Departmentin Partial Fulfilment of the Requirements for the
courseELECRONIC DEVICES AND CIRCUITS (ECE 001)
Technological Institute of the Philippines
