Power Supply Resevoir Size

[AndrewT]

I don't have the spreadsheet.

Take a 200Turn primary and add on a 100Turn secondary.
Apply 120Vac to the primary. The open circuit output voltage will be 120Vac*100T/200T = 60Vac.

Take that same transformer and apply a resistive load to the secondary. Adjust that secondary load until the rated AC current is drawn from the transformer.
The output voltage will now be the "rated output voltage".

That voltage could be 55Vac. If we take that 55Vac as the actual rated output voltage that transformer will be specified as a 120:55Vac The regulation will be [60/55*100] - 100 = 9.090909%, probably specified in the datasheet as either 9% or more accuratly as 9.1%

The turns ratio of that hypothetical transformer is NOT 120/55
The Turns Ratio is 120/60 = 2times.

Find another way to incorporate your 40mA of fictitious output current overhead. The output current is 5Aac when delivering 100W to a 8r0 resistive load.

[fas42]

Phew, Tom, with those posts you're making up for being out of the loop for that period! So, hope your health keeps up for you from now on ...

Yes, the VB thing is what the problem would be with Open Office, we have a m/c with Excel so I'll give it a run there.

And don't apologise about the maths thing - these days my head would explode trying to digest what you've been doing ...

Cheers,
Frank

[gootee]

This version looks pretty good, finally (attached). And now it runs in about 5 seconds instead of 40, on my machine.

I think that the "# of diodes" functionality works OK, now. I was also finally able to get the equation version of the diode Rdiode(i) model to work.

I changed the optional series resistance and inductance fields to be DELTA R and DELTA L, so that users can also SUBTRACT resistance and inductance, as long as it doesn't make the resistance or inductance that represent the secondary's R and L go below zero.

I have not yet looked at the possible turns-ratio issue that AndrewT brought up.

I changed the names and meanings of the peak output voltage and current fields, to avoid further confusion. They are now named "Peak Rload Voltage" and "Peak Rload Current". The additional current drawn by the amplifier or other active load is entered in a separate field, and adds to the "iload" that is used in the calculations, iload being the power supply's output current, not the active load's resistive load's current.

A screen image of the main screen and an image of the schematic of what is simulated for ndiodes = 2 are also attached. (The schematic is one of the ones included in the spreadsheet.)

Tom

[gootee]

I documented some of the equations behind the transformer-rectifier-capacitor power supply spreadsheet, for anyone who is interested in the analysis of these types of circuits. Review comments would be welcome.

PDF document is attached. Sorry about the low image quality. It was exceeding the maximum allowed size.

Cheers,

Tom

Once more with feeling -PDF removed. Hang on, the other post is dated later - Have I just mucked up causality and physics as we know it?

[gootee]

I was curious about how the accuracy of the spreadsheet's waveforms would be affected by stretching out the run time. Since that makes the time-steps larger, it should eventually make the results inaccurate to the point where they are unusable. (We could always just increase the number of steps, to keep it accurate for any longer run times. But that would be a little more involved, because then each plot's row-range settings would need to be adjusted, to use the extra rows of data that would result.)

Anyway, it's not nearly as bad as I thought it might be. I was able to increase the run time from .0375 sec to 0.1 sec with no significant change in the waveforms of the results. Although slight oscillations of the peak output voltage start to appear at durations of around 0.2 seconds, with 4000 time steps, the reported peak value is still at 99.8% of the correct value even out to 2.0 seconds.

Below are some screen shots that show the progression, with 100000 uF of capacitance.

Overall, I am amazed at how much this simple little numerical solver can do. It looks like this tool will also be useful for investigating power supply startup behavior, after all, even with relatively-large reservoir capacitance values.

[gootee]

I should have thought of this sooner.

There is now a user-entry field for the phase angle of the secondary winding's AC input voltage. It can be varied from -90 degress to +90 degrees.

The secondary's AC input voltage is modeled with cos(wt+p). So with the phase angle p = 0, or missing as it was until now, the AC input voltage was at its maximum, at startup. Now it can be varied to be anywhere from zero to its maximum, on either the up-slope or down-slope side of the sinusoid.

Version 0.96 is attached.

Cheers,

Tom

Document removed at OP's request

[gootee]

I was just playing around with the new phase angle setting and it looks like it could be very useful.

The following is just an example, from me just playing with the phase angle setting for the first time, but it might illustrate some of the potential utility of the power supply simulation spreadsheet, and the newly-added phase angle setting for the AC input voltage:

I started out with 10000uF, 100 Watts, 8 Ohms, with a 200VA/44V transformer, with the AC input phase angle at the default zero degrees. (See attached plot.)

I changed the phase angle to 90 degrees, so that the cosine looks like a sine, i.e. it starts at zero. I noticed a much faster rise-time and some overshoot. (See attached plot.)

I wondered if the overshoot would be larger if there was less resistance in the transformer or wiring so I added a "negative 0.1-Ohm" delta-R, to subtract 0.1 Ohm from the series resistance. Wow. The overshoot increased to almost 77 V (versus the nominal 55V or so), i.e. almost to 40%!

I decided to see if adding capacitance could tame the overshoot. I found that by tweaking the C value I could get either overshoot or undershoot. Just for fun, I tuned the C value to 25600 uF, to get no overshoot or undershoot.

For our much-earlier discussion: This looks like it might sometimes be another possible consideration or reason to increase or decrease the C value.

Unfortunately, there is a trade-off, as always, and we can see that in order to eliminate the large voltage overshoot by (in this case) raising C, it would increase the startup current surge by about 50%, in this particular case. Adding 0.1 Ohm to such a circuit might be a better option.

Later,

Tom

[gootee]

Originally Posted by gootee

I documented some of the equations behind the transformer-rectifier-capacitor power supply spreadsheet, for anyone who is interested in the analysis of these types of circuits. Review comments would be welcome.

PDF document is attached. Sorry about the low image quality. It was exceeding the maximum allowed size.

Cheers,

Tom

I should know better than to make changes at the last minute. Also, I added and corrected some things.

A new version of the transformer-rectifier-capacitor power supply analysis document is attached, as a PDF file.

Please, delete any copies of the older version that you may have downloaded. Thanks.

Cheers,

Tom

[gootee]

Originally Posted by gootee

I should have thought of this sooner.

There is now a user-entry field for the phase angle of the secondary winding's AC input voltage. It can be varied from -90 degress to +90 degrees.

The secondary's AC input voltage is modeled with cos(wt+p). So with the phase angle p = 0, or missing as it was until now, the AC input voltage was at its maximum, at startup. Now it can be varied to be anywhere from zero to its maximum, on either the up-slope or down-slope side of the sinusoid.

Version 0.96 is attached.

Cheers,

Tom

Document removed at OP's request

Oops. I guess I asked the mods to remove the wrong document. I was trying to get them to remove the older version of the PDF file, not the spreadsheet.

I have attached the latest version of the spreadsheet to this post.

Tom

[lindjosh]

I've spent the better part of the day reading through this thread and I must say. Excellent looking work you have compiled Tom!