Quick (and probably stupid) rectifier question

[Turbo7MN]

So I've searched around but can't really find what I'm looking for, probably because the answer is such common knowledge. I need to know this quick:

So I built a prototype of an amp I want to scratch build in an old PA chassis. The way it's set up now I used the original half wave voltage doubler (SS) style to give me about 310VDC B+ (this is running a single 7868). Anyway, I'm about to order the stuff for the scratch build but I plan on using a more typical full wave SS rectifier (not voltage doubler or bridge) but I can't find any way to calculate the voltage I need for the power transformer. Can anyone tell me what secondary voltage I'd need to get around 310VDC after the rectifier, or at least tell me how to figure it out? Thanks.

-Darren

[xFallen]

Rather than explain it, you owe it to yourself try this PSU design tool. I have used it for all manner of projects:

http://www.duncanamps.com/psud2/index.html

You can design a variety of supplies and analyzes projected characteristics static and under load. I learned a lot just by playing with the PSU deisgner. Looks like he has a new version out these days. Good stuff.


Barry

[Turbo7MN]

Thanks. Looks like a cool program, but I don't really have time to learn the program right now, I just need a quick answer for this one thing, or a formula. Thanks!

[Enzo]

The crude rule of thumb is based on peak versus RMS. Your AC from a transformer is measured in RMS volts. WHen rectified, the filter cap will charge to more or less the peak voltge of that AC. WIth SS rectifiers, we can ignore the voltage drop of about a half volt. (As opposed to tube rectifiers which will drop tens of volts.)

The relation is Peak = RMS x 1.414. GOing the other way, RMS is about 0.707 times peak.

So to get 310VDC, RMS = 310 x .707 = about 220vAC. That with a full bridge. If you prefer a center tapped setup, then 440VAC center tapped.

Crude but close. And you have to consider curent loads on the transformer and what they do to its voltage. Transformer output is usually measured at its rated current. Draw less current and the voltage will be higher somewhat.

Is the DUncan program really that difficult?

[xFallen]

Originally Posted by Enzo

The crude rule of thumb is based on peak versus RMS. Your AC from a transformer is measured in RMS volts. WHen rectified, the filter cap will charge to more or less the peak voltge of that AC. WIth SS rectifiers, we can ignore the voltage drop of about a half volt. (As opposed to tube rectifiers which will drop tens of volts.)

The relation is Peak = RMS x 1.414. GOing the other way, RMS is about 0.707 times peak.

So to get 310VDC, RMS = 310 x .707 = about 220vAC. That with a full bridge. If you prefer a center tapped setup, then 440VAC center tapped.

Crude but close. And you have to consider curent loads on the transformer and what they do to its voltage. Transformer output is usually measured at its rated current. Draw less current and the voltage will be higher somewhat.

Is the DUncan program really that difficult?

The program is very easy to use to answer the above types of questions, and not much harder to perfor certain load simulations. Very cool.


Barry

[Turbo7MN]

Originally Posted by Enzo

The crude rule of thumb is based on peak versus RMS. Your AC from a transformer is measured in RMS volts. WHen rectified, the filter cap will charge to more or less the peak voltge of that AC. WIth SS rectifiers, we can ignore the voltage drop of about a half volt. (As opposed to tube rectifiers which will drop tens of volts.)

The relation is Peak = RMS x 1.414. GOing the other way, RMS is about 0.707 times peak.

So to get 310VDC, RMS = 310 x .707 = about 220vAC. That with a full bridge. If you prefer a center tapped setup, then 440VAC center tapped.

Crude but close. And you have to consider curent loads on the transformer and what they do to its voltage. Transformer output is usually measured at its rated current. Draw less current and the voltage will be higher somewhat.

Is the DUncan program really that difficult?

Thanks man, exactly what I was looking for. I appreciate it.

The Duncan program isn't too bad now that I've figured out how to actually add stuff, I'll certainly be using it to design stuff from now on. It seems like it's ideal if you know the output of the transformer already though.

So a 220-0-220 looks like what I need. Thanks!

-Darren