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PI Expert FAQs

The following information provides helpful tips on the installation and use of the PI Expert Power Supply Design Software.

  1. General
  2. Setup and Installation
  3. Frequently Asked Questions for PI Expert 6.6 Users
  4. Power Supply Design
  5. Optimization

I. General

  • What's new in the PI Expert Suite v7.0?
    • Multiple Output (MO) Optimization has been added. This new feature allows for fully optimized designs with up to six outputs, including one negative output. Using your specifications, MO optimization takes into account the key operating parameters, transformer stacking arrangements, secondary turns, and output diodes to produce the best possible design with the smallest margin of error, device, and core.
    • Transformer designer is now available as a part of PI Expert, which allows a more convenient transformer design right within PI Expert. Transformer parameters are now updated as your design changes in PI Expert.
    • PI Expert now makes recommendations for the clamp circuit. PI Expert will choose a clamp circuit type based on the output power and calculate all the necessary component values as well as provide the appropriate part numbers.
    • PI Expert makes recommendations for input EMI filtering. PI Expert will choose from a number of EMI filter designs based on the output power and provide filter component values and part numbers.
    • TOPSwitch-HX is now supported in PI Expert, which means that fully automated and optimized designs can be generated using devices from the TOPSwitch-HX family.
    • DPA-Switch is now supported in the Flyback topology in PI Expert.
    • PI Expert now estimates whether or not all of the transformer’s windings will fit in the winding window of the chosen core and bobbin combination. If the windings do not fit, alternate solutions are considered.
    • Custom Component Library and Custom Component Sets are fully supported. This allows you to add your own components to the library and create a set of preferred components for the software to use during optimization and include in your design manually. For example, you can specify the software to only use components (such as transformer cores, capacitors, and diodes) that are readily available in your geographical area.
  • What is contained on the PI Expert Suite v7.0 CD-ROM?

The PI Expert Suite contains complete installation for PI Expert, PI Xls and PI Viewer applications. In addition to the PI Expert Suite software (available through web download), the CD-ROM also contains Power Integrations product and design collateral.Back to TopII. Setup and Installation

  • How do I upgrade previous versions to PI Expert v7.0?

The installation program will detect previous versions of PI Expert and ask you if you want to delete the previous version. You must select "YES" to uninstall all previous PI Expert versions to install PI Expert v7.0.

  • How do I get upgrades to PI Expert v7.0 after I install it on my computer?

Make sure you are connected to the internet . Please use the auto update feature which can be found under Help - Check Latest Updates in the PI Expert, PI Xls, and PI Viewer menus.

  • I am having trouble properly installing PI Expert on my system. What should I do?

Verify that your system meets the minimum requirements: Windows 2000/XP/ Vista, Pentium, 2 GHz processor recommended, at least 90 MB free space, 256 MB system memory is required. 512 MB system memory is recommended.You will need administrator privileges to install on your system. Please contact your system administrator for more details.

  • The new version doesn’t have support for old products. What should I do?

 PI Expert supports devices recommended for new designs.  PI Expert designs created using legacy products can be viewed using the included PI Viewer application.  For PI Xls designs or for additional guidance please contact technical support at PIExpert@powerint.comBack to TopIII. Frequently Asked Questions for PI Expert v.6.6 Users

  • Where is the PI Transformer Designer application?

PI Transformer Designer applications has now been incorporated as part of the PI Expert and PIXls applications. 

  • What is PI Viewer?

This application allows you to conveniently view *.UDS, *.UDX or *.UDF design files created with current and previous versions of  PI Expert. *UDX, *.UDF files are not compatible with PI Expert version v7.0.The PI Viewer allows the user to print or export design files into HTML format

  • What is PI Xls?

PI Xls is included to assist engineers already familiar with Power Integrations earlier excel transformer design spreadsheets.  This tool provides early support for new products and topologies in a familiar spreadsheet format.

  • Is the design file format different in PI Expert v7.0?

No, PI Expert v.6.6 has the same file format as version 6.6. PI Expert v7.0 uses the *.UDS file format. The *UDX and *.UDF formats were used with previous versions, prior to 5.5 and 6.1, and must be converted to work with PI Expert v7.0. This conversion may slightly modify the original *.UDX, *.UDF file results. The PI Viewer is available to review the original content of *.UDX, *.UDF files.

  • Can I open the *.UDX, *.UDF design files created using previous versions of PI Expert?

The user has two choices when opening an old (*.UDX, *.UDF) design file: Review the file in read-only format with the PI Viewer. PI Viewer is also available within the PI Expert Tools menu. Open the file and select the "Yes" option at the startup prompt to automatically convert to PI Expert v7.0 *.UDS format. This file is no longer read-only and may be modified and re-saved. This conversion may modify the original *.UDX, *.UDF file contents. See "Opening a *.UDX, *.UDF file" for more information.

  • I changed the Preferences settings (Main Menu Tools option), but my active design has not changed. What have I done wrong?

The Preferences setting changes you have made will only take effect on your New designs and does not affect your active design. To alter the active design, use the Design Defaults form available through the navigation tree.

  • How do I save my custom power supply input specifications and custom transformer settings?

Use the "Save Custom Settings" option in the Active Design menu to save your custom power supply input specifications and custom transformer settings.

  • Where can I specify custom transformers?

In PI Expert v7.0 the Component library has been expanded to support custom components of all types, including transformers. Users can enter any number of custom cores and bobbins in the component library for the software to use. Additionally you can specify diodes, capacitors, zeners and inductors in the component library. This library can be accessed under the Tools menu, by clicking the Custom Library tab. Users can share individual libraries or all libraries by using the import or export buttons provided.

  • What are component sets?

PI Expert uses component sets to define a collection of components to use when creating, optimizing and documenting a design. Component sets allow you to choose exactly the components that you want to use in a design. A component set is a subset of the Component Library and includes all of the component types including Transformers (composed of Cores and Bobbins), Capacitors, Diodes, Zeners/TVS and Inductors. To use a component added to the component library you must add it to a component set unless you are using the All Records set.PI Expert supports multiple component sets which allows you to have different sets to select from when creating designs for different applications and customers. The Default Library Set, which is composed of all the components included in the Default Component Library, is the default component set that is used when PI Expert is installed.

  • What is the difference between setting up the Preferences and saving the Custom settings?

Saving Preferences works only on your new designs and does not affect active designs. When initiating a new design the Saved Custom settings will be automatically entered into all applicable forms.

  • I have a question that is not answered here. How do I contact PI Expert technical support?

For more information on using PI Expert v7.0 please visit our web site at: www.powerint.com/en/design-support/pi-expert-design-software or send us an e-mail, piexpert@powerint.com, describing the problem (if possible, please attach your design *.UDF, *.UDX or *.UDS design file).Back to TopIV. Power Supply Design

  • Why does PI Transformer Designer use multiple parallel wires in transformer constructions?

PI Expert and PIXls both use multifilar windings. This means that rather than use one thick wire it uses two or three (or more) parallel stands of thinner wire. This minimizes skin effect losses, fills the bobbin width, lowers leakage inductance, and thus provides a more optimized design.

  • In PI Expert and PIXls, what is “maximum terminations per pin”?

PI Expert and PIXls both use multifilar windings in the transformer design. This means that rather than use one thick wire it uses two or three (or more) parallel stands of thinner wire. As more and more parallel wires are used, it becomes difficult to terminate all these wires onto a single pin especially if the wires are thick and the pin is thin as is the case with small bobbins. In this case it is better to split the wires between 2 or 3 different pins for the terminations. The “maximum terminations per pin” specifies how many wires can be terminated onto a single pin and the default is set to 4 wires per pin. For thinner wires this number may be as high as 6 and for thicker wires this number may be as low as 2.

  • The terminology used within PI Expert is unfamiliar to me. Where are the definitions for these terms?

There is a Help button located on the toolbar and pop-up window within PI Expert or you can press F1 function key at any time. Selecting the Help button will launch the Help Utilities consistent with that form or window. You will find answers to common questions, terminology and guidelines to software usage within the individual Help sections.For further details on general power supply terminology we recommend that the user read the applicable Application Notes for the selected devices. (See Help for details).

  • What is the basis for the algorithms used within PI Expert?

For details of the calculations, see the applicable design methodology documents. The PI Expert algorithms are consistent with these references. See application note AN-23 and AN-32 for detailsThe new multiple output optimization algorithm is an exhaustive algorithm that considers several combinations of design variables and then then presents top solutions to choose from. Please see the help system’s documentation on optimization for more information.

  • How can I specify a design with a negative DC output?

PI Expert allows one negative output when the total number of outputs is 2 or more (the negative output cannot be the main output). To work around a design where a single negative output is required simply enter the negative DC output as a positive value. Make sure you remember which output is negative when you determine the transformer pin-out and resulting PCB layout.

  • What determines Transformer maximum power capability (PMAX)?

Transformer power capability is determined using the Area Product method (Ae x Aw). Efficiency, device switching frequency and transformer margin are factored into this calculation.

  • My preferred Transformer does not appear on your list. How can I add it?

In PI Expert v7.0 the Component Library has been expanded on and supports custom transformers (composed of a core and bobbin combination) in addition to custom capacitors, diodes, zeners and inductors. Users can enter any number of custom cores in the component library for the software to use. This library can be accessed under the the Tools menu, by clicking the Custom Library tab. Further PI Expert v7.0 also allows the use of custom component sets whereby users can specify which components may be considered by the software during its optimization run and solutions generation process.

  • What is “Margin on Left” and “Margin on right”?

PI Expert and PIXls provide more flexibility in specifying the margin on which side of the bobbin (left and right side for horizontal bobbin and top and bottom side for vertical bobbin). This is particularly useful in specifying asymmetrical margins.

  • I noticed some inconsistencies with the gapped core effective inductance calculation (ALG). Is this a bug?

PI Expert uses non-integer primary turns within the ALG calculation. In most cases, since primary turns are large, the resulting error is minimal. Please make the necessary changes to the ALG value when communicating with your magnetic vendor.

  • What is the basis for the default efficiency estimates?

Default efficiency is based on the efficiency curves presented in AN-21 (TOPSwitch-II), AN-26 (TOPSwitch-FX) and AN-29 (TOPSwitch-GX). TinySwitch-II efficiency is estimated and based on the evaluation of actual power supplies.These curves estimate power supply efficiency given AC input range and output voltage. For output voltage between 5 V and 12 V, efficiency is estimated using linear interpolation. PI Expert estimates efficiency deviation for outputs outside the 5 V to 12 V range.

  • Can PI Expert help me with package choice and thermal evaluation?

PI Expert can be used in conjunction with AN-21, AN-26 and AN-29 to gain insight into package dissipation. In general, Y-packages and E-packages with suitable heatsinking should be considered when device dissipation exceeds approximately 1.5 W (open frame) or 1 W (adapter/enclosure); assuming a 50 °C ambient temperature.Thermal design can be further hindered by extreme operating temperatures, poor layout, high altitude, inefficient transformer design and/or airflow limitations. When used near maximum current capability, Power Integrations recommends a maximum operating junction (die) temperature of 110 °C for all TOPSwitch, TinySwitch, LinkSwitch and PeakSwitch products. This generally provides adequate design margin to the minimum device thermal shutdown, taking into account device and unit to unit variations.Back to TopV. Optimization

  • Optimization is not solving with the input Capacitor, TOPSwitch/TinySwitch-II and/or Transformer that I wish to use. How can I work around this problem?

If the output power is beyond the capability of the device in question, the Optimization tool will choose the device combination which best suits your requirements. This choice is dependent on Optimization Parameters section within the Active Design on the main menu. If Optimization chooses a device, which is smaller than the preferred device, the user may force the preferred component choice(s). Simply select the desired device from the PI device selection dialog and then from the solutions filter dialog make sure that the core start entry and the core end entry is the same and is the core that you want the software to design with. Then click on the optimize button and allow the software to present solutions with the additional constraints of device and transformer size.Transformer power power processing capabilities are derived using the area-product method (Ae x Aw). Power supply efficiency and switching frequency are factored into this calculation.In all cases, Optimization will choose the optimum input capacitor. The user cannot override this component choice. The user should pursue manual design if an alternate input capacitor is desired. Alternately you can enter a DC input voltage corresponding to the input capacitor average DC voltage and ask the software to redesign with this specification.

  • Why do I get the same efficiency estimate for Cost and Efficiency Optimization?

PI Expert assumes a current waveform parameter consistent with AN-21, AN-26 and AN-29 (varies according to power requirements, AC line voltage and PI Deviceused). Therefore the efficiency estimate does not take account of the change of optimization goal. In practice a prototype using a transformer design optimized for efficiency should have a higher efficiency than that optimized for cost.

  • What is Cost Optimization?

During the cost optimization process a number of designs using different combinations of cores, secondary turns, secondary output stacking configuration and output diodes are scored based upon criteria internal to the software. A list of the top scoring designs is maintained throughout the optimization process. Upon successful completion, the list of top designs is displayed. You can then choose the design which you believe to be the most appropriate for your application.Cost optimization is based on the following key concepts:

  • The smallest PI device that is capable of delivering the power is chosen first.This step is not simply a check to ensure that the device’s rated power, taken from the data sheet, is greater than the power specified. This first step in optimization takes into the account a number of key operating parameters, which include the maximum duty cycle (DMAX), the peak primary current (IP), the reflected output voltage (VOR), and the peak to ripple primary current ratio (KP).
  • The smallest transformer core that is capable of delivering the power is then chosen.Similar to the selection of the proper PI device, the selection of the transformer core is made using a number of key operating parameters. Some of these parameters include flux density (BM and BP), gap length (LG), primary layers (L) and the physical dimensions of the windings within the bobbin window fit factor (FF)
  • What is Efficiency Optimization?

Efficiency optimization is available for the TOPSwitch and DPA-Switch family of devices only. There are two key factors that are crucial to understanding the efficiency optimization method:The PI device capable of delivering the specified power with margin to the device’s current limit is chosen.The PI Expert efficiency optimization routine will first find the smallest PI device capable of delivering the power specified. The software will then reduce the peak to ripple primary current ratio (KP) in an attempt to make the design more continuous. This decreases the peak primary current (IP) which will decrease the peak and RMS currents in both primary and secondary windings. This reduction in current magnitudes increases the overall supply efficiency due to reduced conduction losses.The core capable of delivering the specified power efficiently is then chosen.This step in the optimization routine ensures that the core selected can not only deliver the power but can also do so without significant losses. The losses accounted for are core losses as indicated by flux density (BM), copper losses as indicated by primary layers (L) and primary RMS currents (KP) in addition to leakage inductance indicated by gap length (LG).As in cost optimization a number of designs are then examined and passed on to the optimization process. PI Expert then retrieves a list of the best scoring designs and then displays it.

  • How does Optimization work?

Optimization generates multiple design solutions and compares to an expert design rules database, compiled by the Power Integrations engineering staff. The Optimization engine seeks the minimum design solution that meets, or exceeds, the limits specified in this database.Power Integrations recommends that all design solutions be constructed and performance verified to your specific requirements. This includes independent verification of safety, thermal and system reliability.

  • Cost Optimization provides a result, which generates the warning "Core size may be too small for this power level (Po)". Is this a serious problem?

This message may appear following successful Cost Optimization. Cost Optimization will consider transformers with power ratings (PMAX) within 90% of specified output power. This warning states that the design, running under continuous rated power, is a approaching the maximum capacity for that core/bobbin size. In these cases, further evaluation of power supply thermal performance is recommended.The user may want to consider a solution with a larger core. To generate these results, you must enable Optimization Manual Start Point. Select a larger transformer and reselect Cost Optimization.Back to Top