This now forms a very good basis from which to begin a power supply design.
This specification is now at a point that it can dictate which design paths must
be pursued in order to meet the above specifications and will help to guide the
designer during the design process.
1.5 A Generalized Design Approach to Power Supplies:
Introducing the Building-block Approach to Power
Supply Design
All power supply engineers follow a general pattern of steps in the design of
power supplies. If the pattern is followed, each step actually sets the foundation
for subsequent design steps and will guide the designer through a path of least
resistance to the desired result. This text presents an approach that consists
of two facets: first it breaks the power supply into distinct blocks that can be
designed in a modular fashion; secondly, it prescribes the order in which the
blocks are to be designed in order to ease their “pasting” together. The reader
is further helped by the inclusion of typical industry design approaches for each
block of various applications used by power supply designers in the field. Each
block includes the associated design equations from which the component
values can be quickly calculated. The result is a coherent, logical design flow in
which the unknowns are minimized. The approach is organized such that the
typical inexperienced designer can produce a “professional” grade power supply
schematic in under 8 working hours, which is about 40 percent of the entire
design process. The physical design, such as breadboarding techniques, low-
noise printed circuit board (PCB) layouts, transformer winding techniques, etc.,
are shown through example. The physical factors always present a problem, not
only to the inexperienced designer, but to the experienced designer as well. It
is hoped that these practical examples will keep the problems to a minimum.
All power supplies, regardless of whether they are linear or switching, follow a
general design flow. The linear power supplies, though, because of the maturity
of the technology and the level of integration offered by the semiconductor
manufacturers, will be presented mainly via examples. The design flow of the
switching power supplies, which are much more complicated, will be covered in
more detail in the respective chapters dealing with the selected power supply
technology. The generalized approach is as follows.
1. Select the appropriate technology and topology for your application.
2. Perform “black box” approximations knowing only the design specification
requirements. This results in estimates of semiconductor power losses,
peak currents and voltages. It may also indicate to the designer that the
chosen topology is inappropriate and a different choice is necessary. It also
allows the designer to order any semiconductor samples that may be
required during the breadboarding phase of the program.
3. Design the power supply schematically, guided by the design flowcharts.
4. Build the breadboard using the techniques outlined in the physical layout
and construction sections in the text.
5. TEST, TEST, TEST! Test the power supply against the requirements stated
in the design specification. If they do not meet the requirements, some
design modifications may be necessary. Make “baseline” measurements so
8 Role of the Power Supply within the System and Design Program