Step by Step Example

For this step by step example we’ll design an AC to DC off-line power supply with the following requirements:

Input Specifications:- 85 Vac to 265 Vac- 50 Hz line frequency- 80% Efficiency

Output Specifications:-Multiple loads are required

- LCD Display: 15V / 1A- Battery Charger: 5V / 2A ( this will be the control regulated main output)- Microcontroller: 3.3V / 0.5A

Start: Start your design by deciding what your power supply requirements will be.

The power supply pictured here is an example of a Secondary-Side Regulated evaluation board from Fairchild.

System Requirement PSR Tool SSR Tool

Power range up to 30W up to 100W

Number of Output Loads 1 Up to 3

Lower system cost (no optocoupler circuit) X

Fast Load regulation XTighter output voltage tolerance X X

Next Step: Decide which topology to use for your design.

Our design example requires three loads. So we’ll use the Secondary-Side Regulated (SSR) topology; the PSR design module will support one load only. Click anywhere in the (SSR) picture of the tool to begin your design.

Tool Tip: Information button. Clicking on it will list detailed information. You will find these throughout the tool.

Tool Tips: Before beginning the design, here are some Tool Tips for columns: Design Value, (Use), and Recommended Value

•Design Value: These are the values used by the tool. This value is automatically populated with the Recommended Valuewhen the (Use) box is checked. You can change the Design Value at anytime by clicking in the box and over-writing the value in the box. Error checking is automatically performed after every entry.

• Recommended Value: At the launch of the tool default Recommended Values are displayed based on the current Design Values. Changing a Design Value causes the tool to update all Recommended Values going forward.

•(Use): When this box is checked the Design Value will always equal the Recommended Value. If this box is unchecked, the Design Value remains constant, independent of the Recommended Value.

Next Step: Enter your design requirements into Step 1.

Tool Tip: the 80% Efficiency requirement is entered in step 1d. Click on the to expand. +

Enter your design requirements: “Number of Outputs” check “3 Outputs”, “2nd Output” enter “15”V and “1”A .

Click on Next Step to guide you through the step by step tabs: 2 - 9. This allows you to create an optimized custom circuit design.

Tool Tip: The Auto Complete may be used in any of the steps 1 – 9 at any time to complete the design using the displayed Design Values.

Tool Tip: You can also click on Auto Complete to create a complete flybackpower supply schematic, BOM, and perform circuit simulation; e.g. Steady State, Transient, and AC Analysis.

Next Step: Enter your fine tuned design parameters.

For this design example, we’ll fine tune some parameters; e.g. MOSFET Overshoot factor enter 1.3 and Peak-current-limit deratingfactor enter 93. (Click on Info button for definitions of these parameters.) In response the PSW tool has recommended the Fairchild integrated MOSFET and Controller, FSL126MR.

Click on Next.

Tool Tip: Active tabs will be dark blue. Grey tabs have not been visited.

Tool Tip: You can tune the design for desired circuit performance based on your specific application requirements, guided by calculation results at every step:

•Voltage and Current Stresses on power components •Transformer magnetizing Inductances•Power losses on switches, transformer core and winding…

Tool Tip: Click on part number to obtain product information on Fairchild’s website.

Next Step: Enter your transformer specifications.

The tool recommended the EI28. However, we’re going to pick a core with a larger AeAw product to reduce transformer losses. Check the RM10.

Click on Auto Complete.

Tool Tip: The tool may display CAUTIONmessages within the design steps suggesting ways the design might be improved. These caution messages will only be visible when stepping through the design

Tool Tip: Power loss analysis are displayed in the Step 9. Efficiency tab.

If you Next step through the tool the last step of your design will be your efficiency curves and loss breakdowns by component.

Next Step: Analyze your design.

After completing steps 1 – 9 or clicking on Auto Complete , the tool will display a complete circuit schematic.

Click on the Simulation Schematic tab to simulation your design.

Tool Tip: You can click on the Design tab to jump back into the design and make adjustments. This is the recommended way to make changes to your design. Advanced users may want to make component adjustments by clicking on the component symbol on this schematic. However no error checking will be performed in this case, resulting in a design that could be invalid.

Tool Tip: The tool does not calculate the input filter component values. Displayed values are typical for an x watt converter.

Next Step: Set up AC Input for analysis/simulation.

Click on Transient Analysis to run analysis.

You can click on any one of these three buttons to run an analysis/simulation.

Tool Tip: Double click on load symbol to setup load condition for analysis.

For this design example our AC input is 175 V rms. You can also change the line voltage by over-writing the value or moving the red slider. The tool will translate this value to a DC input voltage for simulation.

For the entered AC line voltage you may choose to simulate at either the Peak or the minimum voltage on the bulk capacitor, Cdc.

Tool Tip: The load settings in the pop-up window are explained in the Info button above .

Next Step: View your Analysis results. Tool Tip: To keep simulation times less than 1 minute, the simulation circuit is simplified. As a result, simulation waveforms will lack the typical high frequency ringing.

Click on ResultAnalysis results can be viewed by clicking on Result, which displays a dynamic waveform calculator, Webscope. Waveforms can be manipulated here; e.g. like an oscilloscope.

OR

Click on the Waveformtab to see a static summary of all analysis results.

Tool Tip: Use checkmarks to display/hide particular waveforms, or use the four black buttons: Hide All, Show All, Move Down, Move Up (to expose a waveform hidden behind another)

Tool Tip: Using Webscope: a dynamic waveform calculator. Pictured here is the Transient Analysis Result.

Tool Tip: In the drop down menus, “(M)” means “between markers”; otherwise the calculation is performed on the entire displayed waveform.

Tool Tip: Drag the markers (vertical cursors) to narrow the time interval for waveform calculations below.

Tool Tip: You can zoom into a waveform by clicking on “Marquee Zoom,” then rubber-band a box around the area you want to expand. To return to full view, hit “Reset Zoom” (second button from the top).

To display the switching frequency, drag the markers to enclose exactly one switching period, then change the first drop-down menu from Δtto 1/Δt. The first number listed below is the switching frequency; the rest remain the differences between the waveform values at the two markers.

Tool Tip: Using Webscope: a dynamic waveform calculator. Pictured here is the Steady-State Analysis Result.

Tool Tip: To order parts, choose your preferred distributor and parts will be auto-selected from the distributor catalog.

Tool Tip: Click on the BOM tab to generate a complete Bill of Materials.

Tool Tip: Click to select a part from the filtered list.

Tool Tip: Create your Bill of Materials.

Tool Tip: To see alternatives or change a selection, click on the “Find” icon …

Tool Tip: Adjust the search filters if desired …

Tool Tip: Click Select to add part number to BOM

Tool Tip: You can save your design on our server to return at a later time to resume working with it. (Your design is confidential, accessible only with your login.)

Tool Tip: Saving your design and creating reports.

Tool Tip: Click on the “Report” tab to generate a PDF summary of your design.

Tool Tip: For technical and tool support or general feedback please send an email.

Tool Tip: You can download and/or print a pdf version of the Report.