PI Expert FAQs
The following information provides helpful tips on the installation and use of the PI Expert power supply design software.
What's new in PI Expert Suite v9.0?
There are a number of new features and functions in version 9.0 of the PI Expert Suite of tools.
- Full support for LinkSwitch-PL and the LinkSwitch-PH families in PI Expert.
- Support for LED families includes TRIAC dimming capability
- Full support for the TinySwitch-4 family in PI Expert.
- Added functionality to export BOM to online web-application to check part availability with prominent distributors
- PI Xls Designer now supports LYTSwitch family of devices in Flyback and buck derived topologies.
II. Setup and Installation
- How do I upgrade previous versions to PI Expert v9.0?
- How do I get upgrades to PI Expert v9.0 after I install it on my computer?
- I am having trouble properly installing PI Expert on my system. What should I do?
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 v9.0.
Note - PI Expert v9.0 is also available in the 64 bit version. To install the 64-bit version of PI Expert Suite v9.0, you need a processor that's capable of running a 64-bit version of Windows OS. The benefits of using a 64-bit operating system are most apparent when you have a large amount of random access memory (RAM) installed on your computer (typically 4 GB of RAM or more).
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.
Verify that your system meets the minimum requirements: Windows XP/ Vista/7, Pentium, 2 GHz processor recommended, at least 250 MB free space, 1 GB system memory is required.
You will need administrator privileges to install on your system. Please contact your system administrator for more details.
III. Power Supply Design
- How is the full schematic interactive and how can I use this image in my documentation?
- What is "Optimize with Fixed Key Parameters"?
- Has the file extension for PIXls designs changed?
- Why does PI Expert and PI Xls use multiple parallel wires in transformer constructions?
- In PI Expert and PI Xls, what is "maximum terminations per pin?"
- The terminology used within PI Expert is unfamiliar to me. Where are the definitions for these terms?
- How can I specify a design with a negative DC output?
- What determines Transformer maximum power capability (PMAX)?
- My preferred Transformer does not appear on your list. How can I add it?
- What is "Margin on Left" and "Margin on right"?
- I noticed some inconsistencies with the gapped core effective inductance calculation (ALG). Is this a bug?
- What is the basis for the default efficiency estimates?
- Can PI Expert help me with package choice and thermal evaluation?
The Full schematic view is a fully functional interactive menu from which various design forms can be directly accessed. Right clicking on any component pops a menu from which the designs forms can be accessed by selecting the "Functional dialog option". Additionally by double clicking any component the user can change the component directly from the schematic. The full schematic image can be exported (through the File > Export option) as Enhanced Metafile (emf) format.
PI Expert allows the user to constrain the optimization engine to optimize with certain parameters being fixed to user selected values. This feature is useful in cases where for example the user wants to use the power of the engine but subtly make certain decisions along the way. For example, you can request the engine to go through the optimization routine but lock the VOR and/or the KP to a specific value. The engine will go through several iterations and present the top solutions with the imposed restrictions. Note that in certain cases you can impose too many constraints on the engine, which can cause the optimization routine to render no optimized results.
Yes. The file extension for all PIXls spreadsheets is now a single extension filename.pixls When you convert your old designs into v9.0 this conversion will automatically take place.
PI Expert and PI Xls 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.
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.
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).
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.
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.
In PI Expert v9.0 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 v9.0 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.
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. For PIXls the parameter M represents half the total margin that is required. Thus if M is specified as 3.0 mm, the software will assume 3.0 mm on the left (or top) and 3.0 mm on the right (or bottom) of the bobbin.
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.
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.
PI expert estimates the heatsink size that will be required for the PI device as well as the secondary side diodes. This size is a function of the type of heatsink used namely copper on PCB, Aluminum sheet metal or Aluminum extruded heatsink.
For copper on PCB heatsinking it is assumed that a square area is used for heatsinking. The shape of the area has a large effect on the effective thermal resistance of the heatsink and therefore the usefulness of the heatsink.
For Al sheet metal type heatsinks a rectangular area of height 20 mm is assumed. The calculations are based on material which is assumed to be Aluminium Alloy (3003 or 5052) with a thickness of 1.6 mm.
For external extruded heatsinks, the software derates the datasheet thermal resistance by 20% and then makes recommendations on required size.
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.
- 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?
- Why do I get the same efficiency estimate for Cost and Efficiency Optimization?
- What is Cost Optimization?
- 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?
- How does Optimization work?
- 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?
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 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.
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.
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:
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.
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.
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 set the desired core in the core start and core end drop down boxes on the "Solutions Filter" dialog during the optimization run.