Key Items for Evaluating the Web Design
Tools:
I assumed that the majority of users would be
relative novices in the field of switching power supply design. I noted the
difficulties I had encountered during the process of evaluating these sites.
Some of the factors I looked for are:
1. Ease of navigation.
2. Understandability of
terminology used.
3. Usefulness of information presented.
4. Detailed
documentation of results -paper copies.
5. User computer revisions of SW
needed to interface to the Web application
6. Ease of building first
prototype
7. Comparing the design with classic approaches and to other
simulation programs.
INTERSIL Web-based Design Program:
The system I ran was:
800 MHz P2, w/
explorer 6.0 & latest JAVA.
Minimum System Requirements are:
MAC System OS X with JAVA version 1.4.2.
Earlier
systems are not supported by Apple and Sun Microsystems.
PC: System 98, ME, XP, and 2000.
Must download most recent JAVA tools to your system (free).
NOTE:
The Intersil Web-based tools were
obviously designed by only IT people. There is no latitude for older
operating systems or JAVA tools. This is a PC tool only. Although MAC OSX
is somewhat supported, it is an Apple-only supported JAVA plug-in.
Procedure:
From The Home Page: http://www.intersil.com.
There are many choices that look like the choice
you may want to choose for the simulation program. But only one choice
leads you to the actual simulation tools. Select "Design iSIM Design Simulation
Tool" or go directly to: http://www.intersil.com/isim/
Here you are presented with several 2 to 4 Phase
VRM buck converters that are meant for the Pentium or Power PC applications.
However, there are five choices that involve other ICs and topologies.
Select the power topology desired: Click on
button "iS" adjacent to the desired design.
You are presented with a list of suggested
component values that can be changed.
IF you were to select "view
schematic", it presents a schematic that can be blown-up to fit the
screen. BUT, if one wants to print the entire schematic, it cannot be
done. The INTERSIL pop-up page set-up is for portrait, but their typical
schematic should be printed in landscape-mode. From schematic window, there is
no way to select the "page Set-up," unless the "print" window of your particular
print driver includes the print orientation buttons for the printer.
Otherwise, there is no way to print the right part of the schematic. Reducing
the scale will make no change in the printout content. (Apparently a bug or an
oversight in the program).
I would suggest printing the datasheet out before
this point, which may include this schematic (with the same component
designation numbers).
Select "Run Simulation":
This produces two Bode plots of the "open-loop"
(control-to-output) and the closed loop Bode plots of the final circuit
elements. The units are in the proper units but difficult to
understand because of the presentation. They do not include the -180 degrees of
phase lag added by the inverting (negative feedback) amplifier. So the
user must add this -180-degree phase lag to the closed-loop phase plot to view
the actual point where the closed loop approaches -360 degrees.
There is no print utility included on Bode plot
screens, so it cannot be printed or saved to the local computer for future
design documentation. Only the "print screen" utility can be used in this
option.
Comparing the simulation results against other
methods:
When comparing the component values presented in
the feedback loop compensation against those derived from my book (Power Supply
Cookbook) and from Ridley Engineering's POWER456, the values were within 10
percent of each other. Therefore, the INTERSIL simulation program uses the
straightforward method of determining open-loop poles and zeros and for placing
the compensating poles and zeros for making the relative optimum closed-loop
compensation.
In summary:
The INTERSIL ISIM tools cover less than 30 percent
of the power management parts in INTERSIL's product portfolio. I would
recommend that the user select the part that he wants to use first, printout the
datasheet, implement the design using the datasheet guidelines, then proceed
into the iSim utility. The designs offered by the simulation program are
for one output voltage, output current and input power system (not directly
changeable). It is good for verifying stability, but not as a design tool.
The user must still design the end-circuit manually.
The presented designs only present the individual
component values. So to change the operation of the selected switching power
supply, such as the output voltage, frequency of operation, overcurrent
settings, etc, the user must still manually perform the design equations or
refer to the datasheet graphs for determining the new values.
The feedback compensation presents the
straightforward approach of assigning the locations of the compensating poles
and zeros within the error amplifier. If you want to change the location of
these poles and zeros, the user must almost start from the beginning in
determining the open-loop pole/zero characteristics. (you can get the main
output filter pole from the open-loop plot ("power train transfer function)).
The zero related to the output filter capacitor cannot be determined from the
open-loop plot. Then the user must relocate the pole/zero frequencies,
then run the classic equations for the actual compensation component values,
which can then be placed within the simulator.
In short, if the user desires any changes to what
was initially presented, the process is completely manual. Without the needed
literary references on-hand, the effort would be a blind shot in the dark and be
very iterative.
It is also very inconvenient because the user
cannot properly print out the schematic and feedback simulator results. This
makes it very inconvenient to document the design for the user's internal design
reviews, if the part were to be included in an actual product.
I encountered some JAVA errors when running the
simulations that had to be re-run to finally get the desired results. This
was more a factor of the server loading than not having the actual required JAVA
within my desktop computer.
This web tool is for the seasoned power engineer
since the design must be completed before the user can derive any useful
information from the simulation tools. Also an accompanying design resource,
such as the "Power Supply Cookbook" might be in order, to quickly refer to the
various design areas within a switching power supply.
There
needs to be some additional work on these tools. They are not very useful for
the occasional power supply designer. Perhaps having a design team that
not only includes the IT department, but also some savvy applications engineers
might be in order.
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