Psud2 Help
i am trying to design a power supply using psud2.
however to model the supply i need to know the transformers secondary resistance,,,
however most manufacturers dont state this on their specs,
how can i get round this, or is a case of buying a transformer, measuring the restance and then working from there.
cheers
soundbadger
oh and just to let you know the transformer i was looking at was the hammond 300bx so if anyone knows the secondary resistance of this tx or has one that they could measure it would be very usefull
i am trying to design a power supply using psud2.
however to model the supply i need to know the transformers secondary resistance,,,
however most manufacturers dont state this on their specs,
how can i get round this, or is a case of buying a transformer, measuring the restance and then working from there.
cheers
soundbadger
oh and just to let you know the transformer i was looking at was the hammond 300bx so if anyone knows the secondary resistance of this tx or has one that they could measure it would be very usefull
"and you ended up adding 200 ohms of resistance in series with the bulk storage of your output stage to reduce ripple by half. The actual output stage essentially has only 10uF to work with; the rest comes from a high impedance source; not good practice for an output stage."
could someone please explain this
cheers
could someone please explain this
cheers
Well, the idea is to have a good deal of capacitance right at the output stage, in your case the B+ is the top side of the SE transformer, with circuit common at the bottom of the cathode resistor.
With large capacitance available, the current requirements of the amp, at all audio frequencies, are supplied by the stored energy in the capacitor. The capacitor is only allowed to be charged up by the wall voltage 120 times every second (60Hz * 2), so the more capacitance you have right at the B+, the better off you are.
The larger the capacitance, the more energy storage you have. As far as the output stage knows, it "sees" a voltage source with a low source impedance, this impedance being primarily the ESR/ESL of the final stage capacitor. Typically, this source impedance will also decrease as you increase the capacitance, ignoring the electrolytic vs. film cap debate. Ideally a zero source impedance at all audio frequencies is pursued, so large capacitance values are selected. There is a practical limit to this goal, of course; no one puts in 1 Farad of capacitance for a 200 mA load.
You are essentially providing a 10 uF cap with let's say, 10 milliohm ESR. That's your voltage source. The larger 100 uF caps you have in your earlier power supply stages are isolated from the B+ portion by the 200 ohm resistor. 10 milliohm in parallel with 200 ohm is 10 milliohm, so the 100uF capacitor essentially does not contribute to the performance of the audio circuit. All it does is serve to reduce ripple.
We are recommending eliminating the resistor to allow your B+ to effectively use the energy in the 100 uF capacitor.
Make sense?
With large capacitance available, the current requirements of the amp, at all audio frequencies, are supplied by the stored energy in the capacitor. The capacitor is only allowed to be charged up by the wall voltage 120 times every second (60Hz * 2), so the more capacitance you have right at the B+, the better off you are.
The larger the capacitance, the more energy storage you have. As far as the output stage knows, it "sees" a voltage source with a low source impedance, this impedance being primarily the ESR/ESL of the final stage capacitor. Typically, this source impedance will also decrease as you increase the capacitance, ignoring the electrolytic vs. film cap debate. Ideally a zero source impedance at all audio frequencies is pursued, so large capacitance values are selected. There is a practical limit to this goal, of course; no one puts in 1 Farad of capacitance for a 200 mA load.
You are essentially providing a 10 uF cap with let's say, 10 milliohm ESR. That's your voltage source. The larger 100 uF caps you have in your earlier power supply stages are isolated from the B+ portion by the 200 ohm resistor. 10 milliohm in parallel with 200 ohm is 10 milliohm, so the 100uF capacitor essentially does not contribute to the performance of the audio circuit. All it does is serve to reduce ripple.
We are recommending eliminating the resistor to allow your B+ to effectively use the energy in the 100 uF capacitor.
Make sense?
soundbadger said:
You really only need four measurements: Measure the DC resistance of the primary and secondary (full winding for a center tapped secondary). Connect the primary to line power and measure the line voltage and the unloaded voltage at the secondary.
Right click on the transformer symbol for the dialog box. Click on the "Ohms" button. A new dialog box will come up. Enter your supply (line) voltage, primary winding resistance, secondary voltage, and secondary winding resistance. It will calculate the transformer parameters for you and will plug them into your supply model when you select OK. Record your measurements, because you will have to re-enter them all if you want to edit this calculation.
Sheldon
All I would do is enter 5% for the regulation, and let PSUD calculate the rest. If and when you get a transformer do the resistance measurements, and plug them in. You will have to know the nominal voltage and the rated current for the transformer. The hammond website lists the rated DC current out of the attached rectifier, you will have to coinvert that to AC current for PSUD by dividing by 1.54.
Depending on if the regulation really was 5% or not, you may end up with a no load voltage difference of 10 or 20 volts. So what, 20 volts here or there in plate supply is nothing.
If your design draws a current near to the rated current of the transformer then regulation wont matter anyway, your transformer will be putting out the nominal voltage, and PSUD and your circuit should match exactly. (in theory)
Depending on if the regulation really was 5% or not, you may end up with a no load voltage difference of 10 or 20 volts. So what, 20 volts here or there in plate supply is nothing.
If your design draws a current near to the rated current of the transformer then regulation wont matter anyway, your transformer will be putting out the nominal voltage, and PSUD and your circuit should match exactly. (in theory)
PSUD2 help needed
right so im designing a power supply in psud2 but dont know what value the transformer impedance. i know what transformer it is but i cant find out the figure.
i have not built an amplifier before so its mostly new, what sort of figure is usual for the transformer impedance .
i have tried a number of figures from 50ohms to 150ohms and get about 20 volts difference in output between the two.
sorry just looked a bit closer in psud2 and the figure says source resistance ,,, how do i work out this?
cheers
soundbadger
right so im designing a power supply in psud2 but dont know what value the transformer impedance. i know what transformer it is but i cant find out the figure.
i have not built an amplifier before so its mostly new, what sort of figure is usual for the transformer impedance .
i have tried a number of figures from 50ohms to 150ohms and get about 20 volts difference in output between the two.
sorry just looked a bit closer in psud2 and the figure says source resistance ,,, how do i work out this?
cheers
soundbadger
If you are going to ask for help (same question in multiple threads, no less), at least pretend to put some effort to read the answers people give you: http://www.diyaudio.com/forums/showthread.php?postid=1339116#post1339116
If it wasn't clear from the previous reply, look at the dialog box you get after clicking on the transformer icon, you'll see that the "source resistance" box has a button to the right labeled "Ohms".
Sheldon
If it wasn't clear from the previous reply, look at the dialog box you get after clicking on the transformer icon, you'll see that the "source resistance" box has a button to the right labeled "Ohms".
Sheldon
Soundbadger,
When you click the trafo icon in PSUDII, next to "offload" voltage, there's a button which takes you into a calculator. Enter the trafo offload voltage and the current specs for the trafo (e.g. for a fullwave rectifier using a Hammond 275-0-275 @ 50mA, simply enter 275V for the voltage and 0.05 for the current. I use 10% for regulation. The calculator then calculates the offload voltage and resistance.
I am not sure how accurate this is, but when I model B+ voltage, I get to within 5V of my empirical values, which at around 350VDC is more than close enough.
NOTE: if you're going to use a bridge rectifier, then for a 275-0-275, you'd enter 550V into the calculator.
I hope this helps and I understand the angst when learning and creating your own PSU. Run your own models, post the schematics and give the specs for your PSU parts, and myself, or someone else will no doubt run it in PSUDII and can check your PSU. Of course, I have to run PSUDII at work as I only have a Mac at home.
People on this forum are extremely helpful and knowledgeable, although it certainly looks better if you attempt your own answer. It reminds me of an experience in France when I was a lot younger. People were not pleased that I expected assistance when I asked for things in English. As soon as I began using my best French (which is quite atrocious even after getting my CSE French) I got loads of help and folk actually found my pronounciation understandable in spite of my thick Lancashire accent.
Hope this helps, and post your PSUDII results when you get some!
Charlie
When you click the trafo icon in PSUDII, next to "offload" voltage, there's a button which takes you into a calculator. Enter the trafo offload voltage and the current specs for the trafo (e.g. for a fullwave rectifier using a Hammond 275-0-275 @ 50mA, simply enter 275V for the voltage and 0.05 for the current. I use 10% for regulation. The calculator then calculates the offload voltage and resistance.
I am not sure how accurate this is, but when I model B+ voltage, I get to within 5V of my empirical values, which at around 350VDC is more than close enough.
NOTE: if you're going to use a bridge rectifier, then for a 275-0-275, you'd enter 550V into the calculator.
I hope this helps and I understand the angst when learning and creating your own PSU. Run your own models, post the schematics and give the specs for your PSU parts, and myself, or someone else will no doubt run it in PSUDII and can check your PSU. Of course, I have to run PSUDII at work as I only have a Mac at home.
People on this forum are extremely helpful and knowledgeable, although it certainly looks better if you attempt your own answer. It reminds me of an experience in France when I was a lot younger. People were not pleased that I expected assistance when I asked for things in English. As soon as I began using my best French (which is quite atrocious even after getting my CSE French) I got loads of help and folk actually found my pronounciation understandable in spite of my thick Lancashire accent.
Hope this helps, and post your PSUDII results when you get some!
Charlie
cbutterworth said:
Charlie, I'm not taking Soundbagger to task for not attempting to find the answer. That's what this forum is for. Nor it an issue of knowledge, as I have found sincere people of all levels respected here. S asked how to calculate the source impedance and got at two valid suggestions. Apparently not finding either expanation adequate, S simply reposted virtually the same question in a new thread. If the responses to the original question weren't clear or not understood, then ask for further clarification - no problem. But to simply ignore attempts to help and repost the same question is bad manners.
Sheldon
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.