Welcome to SW. This is a switcher design program that allows you to design switching power supply interactively. The
menu is accessed by pressing Alt-Space. All the other menus are accessed by pressing Alt-Z, where Z is the first letter of the menu. For example, the "File" menu is pulled down by Alt-F. All menus items are available when you are at the top menu level. )
Press ESC to put this help screen away.
(System) menu
(Alt-Spacebar)
The System menu appears on the far left of the menu bar and is represented by the
symbol. (
When you pull down the
menu, you see
About
About
When you choose the About command from the
(System) menu, a dialog box appears, showing copyright, author and version information.
Press ESC to close the box.
File (Alt-F)
The File menu offers choices for starting a new design, opening old files, save working files, save existing design to a new filename, exit to DOS and back and exiting the program.
Open FExit FDosShell
File
Open (F3)
The Open command displays the Open a File dialog box. In this dialog box you select the design file you want to work on. &
The Open
File dialog box contains:
an input
box with a history list
a list
box to browse the directory
the standard Cancel button
OK action button
an information panel that describes the
selected file
File
Save (F2)
The Save command saves the file that's in the active Edit window to disk. H
Use Save_As(F5) to define file name before executing Save(F2) command. &
The Save
File dialog box contains:
an input
box with a history list
a list
box to browse the directory
the standard Cancel button
Save action button
an information panel that describes the
selected file
File
SaveAs (F5)
The Save_As command opens up the Save File as dialog box with a file name *.SWI, where you can save the file in the active Edit window under a different name, in a different directory, or on a different drive.
Click or choose OK when the new file name, including the drive and directory, has been entered. The Save command will then use the file name defined in the Save_As command. &
The Save
File dialog box contains:
an input
box with a history list
a list
box to browse the directory
the standard Cancel button
Save action button
an information panel that describes the
selected file
File
DOS Shell
With the DOS Shell command, you can leave the program temporarily to perform a DOS command or run another program. Please keep in mind the memory available is the total space minus the SWcad program, and there is about 100K to 200K bytes left for DOS commands. 9
To return to this program, type EXIT at the DOS prompt.
File
Exit
(Alt-X)
The Exit command terminates this program.
Help on Open a File Dialog Box
The Open a File dialog box contains an input box, a file
list, a file information panel, the standard button Cancel, one other action button (Open), plus a history list that's attached to the Name
inputbox.
Name
The Name input box is where you enter the name of the file to load, or the file-name mask to use as a filter for the Files list box (for example, *.*).
Files
FILENM01.SWI
FILENM09.SWI
FILENM02.SWI
FILENM10.SWI
FILENM03.SWI
FILENM11.SWI
FILENM04.SWI
FILENM12.SWI
FILENM05.SWI
..
FILENM06.SWI
\DIR0
FILENM07.SWI
\DIR1
FILENM08.SWI
\DIR2.DIR
The Files list box lists the names of files in the current directory that match the file-name mask in the Name input box, plus the parent directory and all subdirectories.
C:\TP\EXAMPLES\*.SWI
BOOST.SWI 52 Mar 24,1991 12:00pm
The File information panel shows the path name, file name, date, time, and size of the selected file. =
None of the items on this information panel are selectable.
[ OK ]
The OK button opens or saves a new design file and invokes the SWitcher design screen in Open mode.
[ Cancel ]
If you choose Cancel, nothing changes and no action occurs, and the dialog box is put away. M
(Esc always cancels a dialog box, even if a Cancel button does not appear.)
[ Open ]
In the Open a File dialog box, if you choose the Open button SW opens a new design file and places the selected file in SWitcher Design screen.
Schematics
Switch to graphics mode and show schematics. The *.BGI drivers have to be in the same directory as the program directory for graphics to work. (Hardcopy not available)
PartsList
Show the list of parts.
OptimizeDsn
Fine tune input variables to optimize the design.
Close
Close current screen menu and go back to top level. F
SwitcherCAD selects all topologies which are capable of generating the required outputs from the stated input voltage range. A buck ( stepdown) converter for instance is only capable of generating outputs which are lower than the input. The following chart shows the capabilities and/or limitations of various topologies.
Buck (stepdown) L
Output can only be lower than input. Switch current must be at least
equal to output current. One inductor is required.
Boost (stepup) M
Output can only be equal to or higher than input. Output will remain
just below input if the switcher is shut off. Output cannot be shorted without dragging down the input. Switch currents must be at least equal to output current times output voltage divided by input voltage. One inductor is required.
Buck-boost (inverting) I
Output will be the reverse polarity of the input, but may have any
amplitude, limited only by switch breakdown voltage. Switch currents must be at least equal to output current multiplied by the sum of input and output voltage divided by input voltage. One inductor is required.
Flyback (using a transformer) M
Output can be any amplitude or polarity, independent of input voltage.
Switch current may be higher or lower than output current, depending on transformer turns ratio.
Tapped inductor buck converter L
Output voltage can only be lower than input voltage. Switch currents
are lower than output current by an amount dependent on tap ratio and input voltage. N
In some applications there will be several possible topologies. Those
using a simple inductor will usually have higher efficiency, but may require significantly higher switch currents than a transformer or tapped inductor topology. A flyback or buck-boost circuit can generate multiple outputs, with one well regulated, and the others moderately regulated. A buck convertor can also generate multiple outputs, but the total power of the extra outputs must normally be less than one-half of the main output power. The box below the topology list area shows the estimated minimum peak switch current for the selected topology. This can be used as a guide to select an appropriate topology, along with other considerations such as short circuit protection (boost cannot be shorted), simplicity, or personal taste. L
Device selection is based on the capability to operate in a specific
topology and the estimated worst case peak switch currents. This criteria may still yield several devices in many applications. SwitcherCAD makes the final selection by choosing the highest frequency device with the lowest switch current rating, to minimize cost. Lower frequency devices may yield higher efficiency, as will devices with higher-than-required switch current rating. You may override the selected device by clicking on the desired device. The following chart lists the characteristics of each device, grouped by family and ordered by frequency and switch current. ]
Device Frequency Switch Input Switch
Current Voltage Voltage
LT1270A 60KHz 10A 35V 60V
LT1270 60KHz 8A 35V 60V
LT1170HV 100KHz 5A 60V 75V
LT1170 100KHz 5A 40V 65V
LT1171HV 100KHz 2.5A 60V 75V
LT1171 100KHz 2.5A 40V 65V
LT1172HV 100KHz 1.25A 60V 75V
LT1172 100KHz 1.25A 40V 65V
LT1070HV 40KHz 5A 60V 75V
LT1070 40KHz 5A 40V 65V
LT1071HV 40Khz 2.5A 60V 75V
LT1071 40KHz 2.5A 40V 65V
LT1072HV 40KHz 1.25A 60V 75V
LT1072 40KHz 1.25A 40V 65V
LT1074HV 100KHz 5.5A 60V 75V
LT1074 100KHz 5.5A 40V 60V
LT1076HV 100KHz 2A 60V 75V
LT1076 100KHz 2A 40V 75V
Next
Done with input data entry and continue with topology and part selection.
Close
Close current screen menu and go back to top level.
Input Voltages. I
Proper definition of input voltage range is important because many
switching regulator parameters are dependent on input voltage. Ripple current in the output capacitor for instance is maximum for high input voltage on a buck converter, and for low input voltage on a boost convertor. SwitcherCAD calculates most parameters at low input voltage because this is where switch currents are highest, and switch current is the limiting factor for moderate to high current designs. Several parameters in each topology may be calculated at nominal input voltage, and a few, such as peak operating voltages, are calculated at maximum input voltage. SwitcherCAD uses strict interpretation of voltages. Therefore, for negative input voltages use a minus sign in front of the value and enter the largest negative number in the min column. The actual calculations and printout are done using absolute values. N
Minimum and maximum input voltages will define topology and peak switch
currents, so care should be exercised in using accurate numbers. Transient low input voltage conditions on the input must be allowed for, because the capacitors used on the input and output of a switching will normally only allow a [hold-up] time of a few switching cycles (30 to 100 microseconds). Maximum input voltage is usually limited by breakdown voltages, which must never be exceeded, even for times less than 1 microsecond. J
The switcherCAD printout of operating conditions states which input
voltage is used for each parameter. If there is any question about [worst case] conditions, that input voltage should be set to several conditions for additional printouts to guarantee that worst case conditions are covered. For instance, ripple current in the input capacitor of a buck convertor will maximize at an input voltage of approximately twice output voltage, and average diode current will maximize at the highest input voltage. Thought should be given to which input voltages affect thermal conditions. A short transient will probably have to be considered if peak switch current or breakdown voltage is exceeded, but for times less than 30 seconds, it may be ignored for thermal calculations.
Output Currents L
Most switching regulator designs in switcherCAD will operate from the
maximum load current down to zero. They will all shift to [discontinuous] mode operation at some low value of load current, but in general this is not a problem. SwitcherCAD assumes that the maximum stated load current is to be used for calculating worst case switch currents, and that the nominal output current is to be used for calculating thermal conditions and efficiency. If maximum load currents will exist for longer than 30 seconds the nominal current should be set equal to maximum load current. Minimum load current is not used in any of the calculations, but may be compared in the printout with the current where the switcher shifts from continuous to discontinuous mode to see if indeed discontinuous mode is entered.
OptimizeDsn
Help file for optimize design
User will be prompted to specify the Design-Screen first, and then all allowed topologies and parts will be chosen automatically on Selection-Screen. Schematics and parts list are also available for each topology. User can further optimize the design by fine tuning each input variables. Once in SWdesign menus, all top level commands are not accessable anymore, only F1(Help key) is still available for all levels. Hit ESC key to quit SWdesign and go back to top level.
Print
Print design data to printer or text file.
Watch
Highlight the line of interest and click the button or press the W key to put it into watch window for monitoring use. The new line is inserted from the top of the window and will push out the bottom line if three lines have been selected before.
Yes
Go back to previous screen and correct the error.
No
Continue with the erroneous input for topology and part selection. Warning: Results might not be meaningful !!!
Print input, output lines and parts list to printer or file. k
()Input_Eqs : All input variables.
()Output_Eqs : All output variables.
()PartsList : List of parts.
Click OK to print, CANCEL to quit.
Define sorting criteria for capacitor database selection. a
[Set Limits]
()Yes use the entered data as sorting criteria.
()No Ignore sorting criteria.
Select inductor, capacitor or resistor database.
EnableAll
Ignore input data and make all topologies and parts available for selection. Warning: Expect to see garbage outputs and divide by zero errors !!!
(.txt)