SMPS Wizards are available for transformer coupled Flyback designs using the inductor tab and for Buck Regulators using the transformer tab.

Flyback Wizard Documentation: The wizard dialog should be run before doing anything else. The dialog is non-modal. As long as you don't modify the winding structure by moving or adding windings, you can go back and make changes. If you move windings around, the dialog will lock you out. It assumes that you are building a transformer coupled Flyback Power Supply. The data on the top and left side has been set to a reasonable default. It should be changed based on your design specifications and preferences. Here's what the entries mean: These Core Selections are also Available using the Core Tab: Family: A list of core families in the database. Vendor: A list of vendors that supply the Family and Material. Material: The magnetic core materials available from the selected vendor Design Parameters on the Left Side: Frequency: Power Supply Switching frequency. Efficiency: Fraction of input power supplied to the outputs do not include output voltage drops, they should be included in the output voltage specification. RatioIsat/Ipk: Defines the current, Isat, at which the core may saturate. The maximum PWM current should be set below this value. When MD adjusts the gap to calculate inductance, the inductance goes up with reduced gap until the core begins to saturate, then the inductance goes down. MD is allowed to maximize this inductance so that reduced inductance (saturation) may begin slightly above Isat. Primary Duty Ratio: The fraction of a switching cycle that the input switch is turned on. Secondary Duty Ratio: The fraction of a switching cycle that the output switch is turned on. It is assumed that all secondaries switch at the same time. While this is not strictly true, it gives reasonable results for sizing the transformer. Simulation data can improve accuracy. Percent Ripple: The change in current during the Turn-On time divided by the peak current at the end of the charging cycle expressed as a percentage. Primary Power: A calculated value that is the sum of load power divided by efficiency. Winding Data: Winding: An integer number that corresponds to the Spreadsheet winding number. You create new windings using the Insert Button. Voltage: The Power Supply DC Voltage. Current: The Power Supply DC Current. Turns Ratio: A computed value based on previously entered data. Buttons: Previous: Decrements the winding number. Next: Increments the winding number. Delete: Deletes the present winding. Insert: Inserts a winding after the current winding. Close: Hides the dialog. Apply: Fills in the Spreadsheet with requirements if the Lock Design isn't checked. If the "Lock Design" box is checked, the spreadsheet AC and DC currents are updated. This allows you to design at one operating point and evaluate performance at other operating points. Most commonly, the losses over a range of input voltages can be examined. How it Works: The wizard uses the mathematical relations that define a Flyback converter to compute the input data needed by Magnetics Designer. MD need the Peak current, the AC current, DC current and required minimum inductance for each winding. In addition it needs to get the Flux Swing set to half wave and fills in the frequency and Duty Ratio. You can change the default core family, its magnetic properties and vendor. When you have finished entering the data, press apply and MD will go through its auto design process and the wizard will check its lock box. You can return to the wizard and change input voltage and press the apply button to see how the operating point affects your design. With the lock box checked, the Wizard doesn't vary structural parameters, only the Currents that affect the power dissipation. Background: Flyback Power Supplies have a large set of free parameters. In particular, the Primary Duty Ratio and Percent Ripple can be combined to yield a myriad of design possibilities. As the ripple is reduced, the high frequency copper losses are also reduced at the expense of transformer size. When the ripple is increased to 100%, the Power Supply operates in discontinuous conduction mode and you can specify the output duty ratio. In discontinuous conduction mode, the output switch will be turned off when the input switch turns on, reducing switching losses at the expense of increased stress in nearly all other power components. Your design is constrained by the availability of technology and its cost. Even so, there are most likely a number of design approaches that have satisfactory outcomes. The SMPS wizard allows you to explore these combinations and to get detailed Spice simulation models and check out the effect of the wizard input data on important design parameters. Flyback Power Supplies alternate between transformer primary and secondary conduction. The non-conducting winding is exposed to the fields of the conducting windings and the gap field. The non-conducting winding(s) will then develop eddy current losses. These losses quickly increase with frequency. From a time domain perspective, a great deal of loss occurs in the current switching interval. Magnetics Designer accounts for these losses when the <Apply Using Fields> button is pressed. If the windings are barrel wound and extend over the length of the stack, then the <Apply Using Fields> button will add the gap loss term. If you experience a sharp increase in loss, you should move the wire at least 3 gap lengths away from the gap (or move the gap away from the wires if possible). Breaking the gap into a number of small segments is an effective way to reduce eddy current losses. In the limit, a powdered toroid eliminates gap loss. For core materials with distributed gaps, you can effectively eliminate gap loss by pressing the options button and setting the gap field to 1p. Litz wire is always on option; however, you can generally make the wire diameter smaller by increasing the strands and by reducing the ripple current. It's probably worthwhile to make several designs with differing ripple current, primary duty ratio and frequency in order to get a feel for the boundaries of an acceptable design. Optimizing the transformer without considering the effects of Power Supply free parameters could result in an unnecessarily costly design. Another significant Power Supply loss occurs because of leakage inductance. This loss is on the order of Leakage*Ipeak^2*Frequency. Optimized high frequency magnetic devices tend to under fill the available winding area because the increased loss experienced by large diameter wire. The automatic designs produced by MD may fail to fill out a layer. You can increase the number of strands to fill a layer and possibly reduce the wire diameter (increase the AWG index). In doing this, you will reduce the leakage inductance as well as the gap induced eddy current losses. You can use the under fill to move the winding away from the gap, using the Bobbin tab, <Bobbin Thickness> entry. Hints: Turns ratio quantization may affect the accuracy of the turns ratio and winding inductance. To improve accuracy, increase the <Min Turns> button data input. It controls the minimum turns on the primary. Set the <Round Coef.> button value to .5 for best accuracy. To get windings to extend across the bobbin, increase strands and decrease wire diameter. When the number of layers is less than or equal to an integer (usually 1.0), you have the right input. You can enter a number for the Wire AWG and press <Enter>. The recalculation will be done and the Wire AWG data will be high lighted so you can repeat the procedure watching the Number of Layers data. Magnetic devices made in this manner will have the lowest leakage inductance. You can similarly increase the number of strands to extend the width of a winding. Reduce increased temperature rise using <Apply Using Fields> by increasing the bobbin thickness or use the Field Analysis Options dialog to move the gap by setting gap location = 95 (center at 95% of the length). Use smaller diameter wire (the higher voltage winding) nearest to the gap. This winding will have the largest proximity and gap field. Using smaller wire reduces these losses because smaller wire conducts better at higher frequencies than larger wire. Avoid using a single gap under the windings. The gap related eddy current losses increase with fewer gap segments. Working through an example: Start MD and select the inductor tab. Then press the SMPS Wizard button. Enter 150 for Voltage then press insert. Enter 5.5Volts and 10Amps for the new winding. Press Apply. Press the bobbin tab, notice that the first winding extended into a second layer. Go back to the inductor tab and increase the Wire AWG to 22 to get 1 layer. Now increase the secondary wire AWG to 16 and increase its strands to 4 get 1 layer. Press Apply using fields, note the temperature increase. Go to the bobbin tab and increase thickness to center the winding. Go back to the inductor tab and Apply using fields. The increased spacing increased leakage inductance, reducing eddy current loss, saving .4 Watts. To make this design work; the strands need to lie flat in a single layer, they can't be twisted. Alternatively, you could have used Litz wire with its increased cost and handling difficulties. Now go to the IsSpice tab and copy the netlist from the copyright notice to the end. Then open the FlybackTemplate300-5.dwg and paste the models into the X11 subcircuit. To do that, select the TranSubckt configuration and double click on X11. Then double click on the .SUBCKT data field. Then select the part of the model to be replaced and paste the new model in. That's a shortcut that avoids making new library entries when you are doing what-if analyses. In the model you can see several important parameters. First, Lmag is the primary side switched inductance and the Efwd2 gain (.1154 is the turns ratio). You will need to modify the main circuit parameters for the Avg, AvgSubck and AvgSubcktLs configurations. You can also keep the schematic symbol up to date with the correct turns by selecting the transformer and choosing Edit Symbol in the Edit menu. After correcting the symbol nomenclature, select replace on drawing from the File menu. After running a transient simulation, you can measure the AC and DC currents in the windings and update the inductor spreadsheet to refine your loss predictions. Buck Regulator Wizard Documentation: The wizard dialog should be run before doing anything else. The dialog is non-modal. The dialog is non-modal. As long as you don't modify the winding structure by moving or adding windings you can go back and make changes. If you move windings around, the dialog will lock you out. It assumes that you are building a transformer coupled Buck Regulated Power Supply. The data on the top and left side has been set to a reasonable default. It should be changed based on your design specifications and preferences. Here's what the entries mean: These Core Selections are also Available using the Core Tab: Family: A list of core families in the database. Vendor: A list of vendors that supply the Family and Material. Material: The magnetic core materials available from the selected vendor Design Parameters on the Left Side: SMPS Type: Choose one of the 3 topologies. Forward: The topology is half-wave, it has DC current and lets the core relax back to its residual flux. Push-Pull: Center-taps primary and secondary windings. It has symmetric flux swing and DC current in its windings. Bridge: Requires full wave switching on primaries and secondaries. There is no DC current. Frequency: Power Supply Switching frequency, for Push-Pull and Bridge converters, the PWM frequency is twice the transformer frequency. Efficiency: Fraction of input power supplied to the outputs; it does not include output voltage drops, they should be included in the output voltage specification. Primary Duty Ratio: The fraction of a switching cycle that the input switch is turned on. Secondary Duty Ratio: The fraction of a switching cycle that the output switch is turned on. It is assumed that all secondaries switch at the same time. While this is not strictly true, it gives reasonable results for sizing the transformer. Simulation data can improve accuracy. Percent Ripple: The change in current during the Turn-On time divided by the peak current at the end of the charging cycle expressed as a percentage. Primary Power: A calculated value that is the sum of load power divided by efficiency. Winding Data: Winding: An integer number that corresponds to the Spreadsheet winding number. You create new windings using the Insert Button. For Push-Pull, there will be a pair of windings for each power supply input or output voltage. Voltage: The Power Supply DC Voltage Current: The Power Supply DC Current Turns Ratio: A computed value based on previously entered data Switched Inductor: A computed value that you should use in the output stage Buttons: Previous: Decrements the winding number. Next: Increments the winding number. Delete: Deletes the present winding. Insert: Inserts a winding after the current winding. Close: Hides the dialog. Apply: Fills in the Spreadsheet with requirements if the Lock Design isn't checked. If the "Lock Design" box is checked, the spreadsheet AC and DC currents are updated. This allows you to design at one operating point and evaluate performance at other operating points. Most commonly the losses over a range of input voltage can be examined. How it Works: The wizard uses the mathematical relations that define a Buck regulated DC-DC converter to compute the input data needed by Magnetics Designer. MD needs the Average voltage, the AC current and DC current for each winding. In addition it needs to get the Flux Swing set to half wave for Forward the topology and fills in the frequency and Duty Ratio. You can change the default core family, its magnetic properties and vendor. When you have finished entering the data, press apply and MD will go through its auto design process and the wizard will check its lock box. You can return to the wizard and change input voltage and press the apply button to see how the operating point affects your design. With the lock box checked, the Wizard doesn't vary structural parameters, only the Currents that affect the power dissipation. Background: Buck regulators have fewer free parameters than the Flyback topology because the switched inductor isn't included with the transformer. When comparing Forward and Flyback designs, the Flyback transformer will be bigger and/or lossier. The percent ripple can be combined with duty ratio to yield a myriad of design possibilities. The design point is usually for the highest load power and it usually has ripple less than 100%. The trade-off between ripple and stress is nearly the same as discussed for the Flyback designs. The Forward topology also carries the concern for transformer saturation during start-up. You can multiply the ratio of (saturation flux density) / Bac times the Edt value in the spreadsheet to get the turn-on Volt-second capacity. By adding a gap to reduce the magnetizing inductance, you can use the PWM sensed current to limit the turn-on volt-seconds (Lmag = Vdt / Imax). Frequently the minimum gap does the trick --- this gap also adds slope compensation! Start MD and select the transformer tab. Then press the SMPS Wizard button. Enter 28 for Voltage then press insert. Enter 5.5Volts and 10Amps for the new winding. Change the on duty ratio to .5 and the ripple to 25% Press Apply. Press the bobbin tab, notice that the windings aren't spread across the bobbin. You should spread windings across the bobbin by increasing the strand in each winding to 6 which reduces the leakage inductance from 96nH to 32nH. For low voltage designs, the turn-off over shoot is limited to Vthreshold*Leakage/Lsource. Low leakage inductance can eliminate the need for snubber components. Press Apply using fields; note the temperature didn't change much. That characteristic of barrel wound transformers when the windings spread all the way across the bobbin. To make this design work; the strands need to lie flat in a single layer, they can't be twisted.. Now go to the IsSpice tab and copy the netlist from the copyright notice to the end. Then open the Forward Template, FwdTemplate.dwg and paste the models into the X2 subcircuit. To do that, select the TranSubckt configuration and double click on X11. Then double click on the .SUBCKT data field. Then select the part of the model to be replaced and paste the new model in. That's a shortcut that avoids making new library entries when you are doing what-if analyses. In the model you can see several important parameters. You also need to make L2, the switched inductor 5u as shown in the SMPS wizard. Run the TranSubckt configuration using the tran 2m simulation setup. You will need to modify the main circuit parameters for the Avg and AvgSubck configurations by changing the turns ratio, N=.6667, Lmag=26u and L=17.5u. You can also keep the schematic symbol up to date with the correct turns by selecting the transformer and choosing Edit Symbol in the Edit menu. After correcting the symbol nomenclature, select replace on drawing from the File menu. Notice that the magnetizing inductance provides slope compensation of MC=.15 for the Forward_ID PWM model you need to enter MC=.15; however, the Forward_I PWM model calculate this effect using the Lmag paramter. After running a transient simulation, you can measure the AC and DC currents in the windings and update the inductor spreadsheet to refine your loss predictions.