Just a quick power supply capacitance question

[markiemrboo]

Originally posted by BWRX
The attached schematic is the correct way to make two regulated split rail supplies from a dual secondary transformer using 4 positive linear regaulators.

Truly fantastic I can't thank you enough.

I will see if I have enough parts to try this out tomorrow.



If I understand correctly, in doing this, I presume that because the virtual grounds after the regulators are... well.... virtual, and 'floating' (I think that's correct?) they shouldn't be connected together to safety earth? This would put me right back where I started I think and defeat the whole purpose of isolating them, right?

[BWRX]

Originally posted by markiemrboo
If I understand correctly, in doing this, I presume that because the virtual grounds after the regulators are... well.... virtual, and 'floating' (I think that's correct?) they shouldn't be connected together to safety earth? This would put me right back where I started I think and defeat the whole purpose of isolating them, right?

Since both grounds are now floating they could be connected together without any problems. I wouldn't directly connect them together to each other or to safety ground. There are other recommended ways of doing it with diodes, a resistor, and a cap. I believe Rod Elliot has an explanation of it on his ESP web pages.

If the source you will be using is single ended and has a common ground for both channels you will in fact be connecting the grounds of both power supplies through the source when all is said and done.

This circuit is deceptively simple but you have to know what's going on inside the black boxes (the regulator ICs) in order to see what the issue is. I admit I had to let it stew in my brain for a little while before realizing what the problem was.

[markiemrboo]

Originally posted by BWRX


Since both grounds are now floating they could be connected together without any problems. I wouldn't directly connect them together to each other or to safety ground. There are other recommended ways of doing it with diodes, a resistor, and a cap. I believe Rod Elliot has an explanation of it on his ESP web pages.

If the source you will be using is single ended and has a common ground for both channels you will in fact be connecting the grounds of both power supplies through the source when all is said and done.

Yeah, I've made a 'disconnecting network' as on his site. I was just wondering if I could still connect the "0v" outputs of the supplies to that still. Seems I can then, but I think I will have to sleep on that one

This circuit is deceptively simple but you have to know what's going on inside the black boxes (the regulator ICs) in order to see what the issue is. I admit I had to let it stew in my brain for a little while before realizing what the problem was.

I have only just learnt the basics of 'the transistor', bias and all that is still a tad over my head, but I managed to make a working fan controller for my computer and actually understand it. So... I probably didn't really stand much of a chance if you need to know what's going on inside the regs

Thanks again though. I am gonna get some sleep now. Good night all.

[Nuuk]

Brian, thanks for sorting out this issue and explaining it so well! I have now edited the options diagram on Decibel Dungeon, and added a note (that includes a link to your post).

[markiemrboo]

Originally posted by Nuuk
Brian, thanks for sorting out this issue and explaining it so well! I have now edited the options diagram on Decibel Dungeon, and added a note (that includes a link to your post).

Just got another bridge rectifier to do this today. It still doesn't seem to work as expected. I have tried with four bridge rectifiers initially, two for one regulated power amp supply and the other two for the regulated preamp supply.

This time, the power amp negative rail is at -12.8v and positive at the expected 28v. The preamp supply is correct at +-13.8v. Rather than the power amp supply being OK and the preamp negative rail being that of the power amp negative rail.

When I disconnect the preamp supply the power amp supply negative rail measures the expected -28v.

Thoughts?

[BWRX]

To clarify, you have four positive regulators wired up as shown in this schematic and RAIL1 is supposed to be +/-28V while RAIL2 is supposed to be +/-14V, but RAIL1 is +28V and -12.8V and RAIL2 is +/-14V. Correct?

I thought isolating the input voltages by giving each regulator its own bridge rectifier would fix the problem but apparently there is still interaction between the negative rail regulators. The problem still lies with the negative rail regulators trying to regulate two different voltages while sharing a non galvanically isolated input.

[markiemrboo]

Originally posted by BWRX
To clarify, you have four positive regulators wired up as shown in this schematic and RAIL1 is supposed to be +/-28V while RAIL2 is supposed to be +/-14V. Correct?

Hi BWRX,

This is correct. Well, this is what I was hoping to achieve rather. What I am getting, however, is RAIL1+ = 28v, RAIL1- = -12.8v, RAIL2+ = 13.8v and RAIL2- = -13.8v.

[BWRX]

Ok. This requires some more brain power. I'll think it over some more tonight after work.

One thing to try would involve putting a resistor in between the bridge rectifier and the input of the negative rail preamp regulator circuit. The value of the resistor would depend on the current draw of your preamp but a good value would probably be in the neighborhood of 400-1kohm with at least a 1/4W power rating.

[markiemrboo]

Originally posted by BWRX
Ok. This requires some more brain power. I'll think it over some more tonight after work.

Thanks very much for the continued help, really appreciate it!

Thinking about it, it does seem slightly different than before. The negative rail isn't identical to the negative rail of the other supply, it's about 1v lower!

e.g (just to clarify)

before, I had:
+28v, -28v
+14v, -28v

now I have:
+28v, -12.8v
+14v, -14v

Look forward to hearing from you again soon, and enjoy the rest of your day at work

[markiemrboo]

Just thought I would post with some info, which may or may not help.

I figured exact voltages would help. So rather than try and remember them, I wrote down the outputs.

It was actually:

Power amp: +28.5v, -12.6v
Pre amp: +13.6v, -13.6v

There's a mysterious 1v difference here.

Also, I measured the output from the caps for the power amp supply, still with the regulator (+28.5v and -12.6v) connected, and I am still actually seeing an ordinary / normal +36v from both.

Just as a reminder, when I disconnect the preamp regulator the power amp supply works as normal (+-28.5v).

The outputs are *not* connected to any kind of load at all, and I am not taking the 0v outputs to safety earth. Quite frankly, until I am getting the correct output voltages I am a bit scared to! Perhaps I should be? But I think it should be measuring correct without doing this anyway..?

Maybe something here is significant somehow, I don't really know!