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When I was designing an off-line (i.e. AC Line-powered) 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 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.
LTSPICE Schematic:
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.)
LTSPICE Schematic:
This power supply produces +/-28VDC at up to 5 Amps each, and also has +/-18VDC outputs for opamp-type circuitry. I originally designed this power supply for an audio power amplifier; a chipamp or gainclone type. It is designed to run from an AC mains transformer that has dual secondary windings of 30V RMS each, but could be modified to use other secondary voltages. And other adjustable linear regulators could be used in place of the LT-1084 shown.
With relatively large-value capacitors on the main 5-Amp regulators' adjust pins, this supply has very low output ripple voltage. But, to ensure that the main regulators' maximum input-to-output differential voltage specification is not exceeded during start-up, it was necessary to add the soft-start circuits.
A convenient star ground simulation scheme is used, including simple parasitic impedance elements, to make it easier for the user to begin to experiment with the sharing of various ground conductors by return currents, and to investigate the effects of different lengths and sizes of PCB traces or wires.
This power supply simulation models many parasitic effects, including capacitors' ESR (Equivalent Series Resistance), inductance, and leakage current, and PCB traces' or wires' resistance and inductance.
There is nothing very novel or different about this PSU design, except perhaps that it uses simple MOSFET-based soft-start (inrush current limiter) circuits to enable the use of extra-large capacitors on the main regulators' adjust pins, to provide very low output ripple.
The main purpose in presenting complete, working spice models was to enable others to more-easily begin to use spice simulations to investigate (and "tweak") power supply and other circuits' behaviors, including such things as star grounding and parasitic impedances, and, for example, the effects of allowing the 'wrong' currents to share a ground-return conductor.
LTSPICE Schematic:
This power supply produces +/-22VDC at up to 4 Amps each. It doesn't have the +/-18VDC outputs for opamp-type circuitry, like the one above. But that could be added, similarly. I originally designed this power supply for an audio power amplifier; a chipamp or gainclone type. It is designed to run from an AC mains transformer that has dual secondary windings of 25V RMS each, but could be modified to use other secondary voltages. And other adjustable linear regulators could be used in place of the LT-1084 shown.
With relatively large-value capacitors on the main 5-Amp regulators' adjust pins, this supply has very low output ripple voltage. But, to ensure that the main regulators' maximum input-to-output differential voltage specification is not exceeded during start-up, it was necessary to add the soft-start circuits.
A convenient star ground simulation scheme is used, including simple parasitic impedance elements, to make it easier for the user to begin to experiment with the sharing of various ground conductors by return currents, and to investigate the effects of different lengths and sizes of PCB traces or wires.
This power supply's simulation includes (and uses) a Spice model of a toroidal power transformer, made directly from actual measurements, as described father above on this webpage. In this case, it is a Hammond 180L50 model 120VA toroidal power transformer, with both the dual primary and dual secondary windings in parallel, giving it a rating of 120V --> 25V @ 4.8A. Also included is a simple model of the AC Mains supply, as well as snubbers for the transformer and for the smoothing capacitors.
This power supply simulation models many parasitic effects, including capacitors' ESR (Equivalent Series Resistance), inductance, and leakage current, and PCB traces' or wires' resistance and inductance.
There is nothing very novel or different about this PSU design, except perhaps that it uses simple MOSFET-based soft-start (inrush current limiter) circuits to enable the use of extra-large capacitors on the main regulators' adjust pins, to provide very low output ripple. (Erratum: Note that the text on the schematic that refers to "C2 and C5" should say "C2 and C12".)
The main purpose in presenting complete, working spice models was to enable others to more-easily begin to use spice simulations to investigate (and "tweak") power supply and other circuits' behaviors, including such things as star grounding and parasitic impedances, and, for example, the effects of allowing the 'wrong' currents to share a ground-return conductor.
LTSPICE Schematic:
A 'VACTROL' is a particular type of analog optical isolator (aka 'optoisolator'), made by encapsulating an LED and a photocell (aka LDR, or Light-Dependent Resistor), together in a light-tight package. By varying the current through the LED, the resistance between the LDR leads can be controlled. In the case of the VTL5C2, an LED current from 0 mA to 40 mA chnages the LDR's resistance from roughly 2 megOhms to a few hundred Ohms.
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