LTspice tool for power amp power supply component evaluation
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Software Tools SPICE, PCB CAD, speaker design and measurement software, calculators

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
andy_c
Banned

Join Date: Apr 2003
LTspice tool for power amp power supply component evaluation

It's lonely in here!

I thought I'd post something that might be useful if you're evaluating power supply components for a power amp. It's an LTspice simulation that allows you to enter some simple transformer and filter capacitor parameters, specify a sinusoidal or other current to be delivered to a load, and look at things like ripple on the supply voltage, sag in output voltage with load, primary RMS current for specifying fuses and so on.

The model for the transformer assumes two secondaries with a center tap. It makes use of two simple ideal transformers with primaries in parallel and secondaries in series. It's meant to be fairly simple and fast to simulate, so there's no transformer saturation effects or inductance taken into account. The output voltage drop under load is modeled as a simple resistor in each secondary. All component values, peak output currents, line frequency, output frequency, etc. are specified in .PARAM statements so that individual element values don't need to be tediously specified. Each .PARAM statement has a comment explaining what it is and its units.

Here's how it works. First, find the specification of a transformer you're thinking of using. Calculate the turns ratio N as the ratio of the no-load output voltage of a single secondary to the primary voltage at which this is specified. Specify N in the corresponding .PARAM statement. Next, find the value of transformer output resistance Rs by taking the change in transformer output RMS voltage delta_v from no-load to a specified RMS load current Irms. Transformer vendors assume a resistive load and no rectifier here, such that the load current in this case is sinusoidal. Then Rs = delta_v/Irms. Enter this in the .PARAM statement. Then enter the estimated filter capacitor value.

The peak load current and its frequency are specified by Ipeak and sigfreq respectively. The total quiescent current IQ in the output stage can be specified. The sneaky part of the simulation is the calculation of the current drawn from each supply. These currents are computed by nonlinear current-controlled current sources which use the table() function. For peak load currents less than or equal to twice IQ, the currents drawn from each supply will be sinusoidal. This assumes push-pull operation, and by specifying a large IQ, a class A amp can be simulated. There are two simulation files, one for unbalanced and the other for balanced amps. For the unbalanced amp where the peak load current is much larger than the quiescent current, each supply current is essentially a half-wave rectified signal. The corresponding case for a balanced amp gives a full-wave rectified current on each supply. The diode parameters were modified from an OnSemi part I found, such that they match a good 35A bridge rectifier.

There's also a third simulation file called "Ramp_table_if.asc". This is just an example from the Yahoo LTspice group that explains how the table() function works for nonlinear controlled sources. The file "Rectifier_bal.asc" is for a balanced amp, and "Rectifier_unbal.asc" is for unbalanced.
Attached Images
 power_supply.png (13.2 KB, 521 views)
Attached Files
 Rectifier.zip (4.2 KB, 153 views)

Last edited by andy_c; 23rd August 2009 at 05:14 PM.

 23rd August 2009, 06:01 PM #2 megajocke   diyAudio Member     Join Date: Jan 2003 Thank you for sharing! That table thing looks very useful and flexible. I usually use the min(x, y) and max(x, y) functions for that kind of thing, but this looks more flexible.
 23rd August 2009, 06:10 PM #3 andy_c   Banned   Join Date: Apr 2003 The table() is a bit weird because the output value is assumed constant outside the range of the table points. That's why I put that silly 1000A limit point in there. But you can see from the Yahoo group example that it's not nearly as messy as multiple nested if() functions.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Room Acoustics & Mods     Music     diyAudio.com Articles     Car Audio     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post Thunau Power Supplies 12 16th February 2007 05:21 AM destroyer X Solid State 91 25th September 2006 05:36 AM HenryM Chip Amps 0 20th January 2005 06:53 PM ericpeters Swap Meet 0 14th January 2005 03:21 PM

 New To Site? Need Help?

All times are GMT. The time now is 08:17 PM.