When I was designing an off-line boost-mode switching power supply, I wanted to model the power transformer, to be able to also simulate the inrush current and other startup behavior. After doing some searches and asking some questions in discussion groups at Google Groups (Usenet message-traffic archive; a goldmine!) and DIYAudio, and downloading some technical
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papers, including this excellent PDF about Modeling Transformers (PDF), I developed the LTSPICE simulation shown below. In the final version shown, only the simple physical measurements need to be entered (the portions inside the solid boxes), and the model parameters are then calculated automatically, using equations from the PDF referenced above. This model should be valid for simple single primary / single secondary transformers, and also appears to be valid for dual primary / dual secondary transformers when both the primary windings and secondary windings are wired in parallel. To download the LTSpice ". ASC" file for the schematic above, Right-Click on the following link and then select "Save Target As". Save the file WITHOUT the ". TXT" that`s at the end of the filename. This type of DC SERVO is meant to keep the DC offset voltage at the output of an amplifier at about zero volts. Typically, a DC Servo is used with an audio amplifier so that AC-coupling/DC-blocking capacitors can be omitted from the signal path. (UPDATED, 23AUG07: REMOVED SIMULATED-WIRE-IMPEDANCE INDUCTORS FROM POWER SUPPLY LINES, TO AVOID NUMERICAL PROBLEMS WITH SPICE`S INTERNAL SOLVER. CHANGED TEST-LOAD`S RESISTANCE TO 8 OHMS FROM 50K. COMMENTED-OUT GMIN-CHANGING SPICE DIRECTIVE. ) To download the LTspice ". ASC" file for the schematic above, Right-Click on the following link and then select "Save Target As". Then change the filename so you save...
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