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SPICE MODELING AND SIMULATION OF ELECTRONIC CIRCUITS AND COMPONENTS

(C) COPYRIGHT 2007, T.P. GOOTEE.
PERMISSION TO USE THIS MATERIAL IS GRANTED ONLY FOR NON-COMMERCIAL USE.
IF COMMERCIAL USE IS DESIRED, CONTACT TOMG@FULLNET.COM .

This page has some of the circuits and component models that I have developed with LTSpice.

Linear Technology Corp's LTSpice is a wonderful, free, very-easy-to-use software package that is extremely useful for drawing electronic schematics and simulating circuits. Along with the circuit and component schematics and models, below, I have included links to download the LTSpice files for them, so anyone can use them with LTSpice.


To download LTSpice, Right-Click on the following link and then select "Save Target As": Right-Click to DOWNLOAD LTSPICE


There is a truly-excellent discussion and support group, for LTSPICE users: Yahoogroups LT-SPICE group.



ON THIS PAGE:

TRANSFORMER MODEL FROM MEASUREMENTS

DC SERVO FOR AUDIO AMPLIFIER

QUAD 28V 5A & 18V DC POWER SUPPLY, WITH LOW RIPPLE & SOFT START

DUAL 22V 4A DC POWER SUPPLY, WITH LOW RIPPLE & SOFT START

MODEL FOR Perkin-Elmer/Vactec VTL5C2 VACTROL

DOWNLOAD SPICE MODELS FOR COMPONENTS









Modeling a Power Transformer Directly from Measurements:


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:

Power Transformer Model from Measurements


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.

Right-Click to DOWNLOAD LTSPICE TRANSFORMER MODEL











DC SERVO FOR AUDIO AMPLIFIER:


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:

DC SERVO FOR AUDIO AMPLIFIER


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 the file _WITHOUT_ the ".TXT" that's at the end of the filename.

Right-Click to DOWNLOAD DC SERVO SCHEMATIC

You should also download the LTspice ".PLT" file for the schematic above. Right-Click on the following link and then select "Save Target As". Then change the filename so you save the file _WITHOUT_ the ".TXT" that's at the end of the filename.

Right-Click to DOWNLOAD DC SERVO PLOT SETTINGS

To run the DC_SERVO.ASC simulation, you will also need to download the OP275 and OPA541E model files, to the SAME FOLDER as the dc_servo.asc file.

To download the LTSpice ".SUB" files for the two models, and the OP275 ASY file, Right-Click on each link and then select "Save Target As".

Change the filename to save the file WITHOUT the ".TXT" that's at the end of the filename. Put them in the same folder as the DC_SERVO Schematic.

Right-Click to DOWNLOAD OP275 OPAMP MODEL

Right-Click to DOWNLOAD OP275 OPAMP ASY

Right-Click to DOWNLOAD OPA541E CHIPAMP MODEL











QUAD 28V 5A & 18V REGULATED DC POWER SUPPLY
WITH LOW RIPPLE AND SOFT START:


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:

QUAD DC POWER SUPPLY


To download all of the LTspice files needed for the schematic above, Right-Click on the following link and then select "Save Target As". After downloading, copy the QUAD_PSU_28V.ZIP file into its own folder and unzip its contents.

Right-Click to DOWNLOAD DC POWER SUPPLY SCHEMATIC AND MODELS, ETC

To run the QUAD_PSU_28V.ASC simulation, you will also need to use LTspice's ALTERNATE SOLVER. Instructions for selecting the Alternate Solver are on the schematic.











DUAL 22V REGULATED DC POWER SUPPLY
WITH LOW RIPPLE AND SOFT START:


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:

DUAL +/-22V DC POWER SUPPLY


To download all of the LTspice files needed for the schematic above, Right-Click on the following link and then select "Save Target As". After downloading, copy the DUAL_PSU_22V.ZIP file into its own folder and unzip its contents.

Right-Click to DOWNLOAD DC POWER SUPPLY SCHEMATIC AND MODELS, ETC

To run the DUAL_PSU_22V.ASC simulation, you will also need to use LTspice's ALTERNATE SOLVER. Instructions for selecting the Alternate Solver are on the schematic.











MODEL FOR Perkin-Elmer/Vactec VTL5C2 Vactrol:


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.

To download the LTspice model, symbol, and test-circuit/plot files for the VTL5C2 Vactrol, Right-Click on the following link and then select "Save Target As". After downloading, copy the VTL5C2.ZIP file into its own folder and unzip its contents.

Right-Click to DOWNLOAD VTL5C2 LTspice FILES.



NEED more SPICE component MODELS? Try HERE!!

You'll find a page with links to over 20,000 downloadable Spice models for electronic components!!

Another great site, with many, many downloadable spice models, is HERE.



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