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 22nd April 2005, 07:09 AM #11 Bakmeel   diyAudio Member     Join Date: Jan 2002 Location: The Netherlands Bowdown... Wait a second.... In your first post you mention that your supplier gave you a higher voltage rating because of the regulation.... Maybe he was right I can't read your mind, but if i'm right, your 100V is based on the calculation of 71VAC * 1.4 = 100V right? The basic square root of two rule. Now, the AC rated voltages for trannies are usually given under full AC load. When you apply rectification, you would tend to believe that you are dealing with peak voltage. This is only true in an unloaded situation. For a DC load no higher than 0.63 times the rated AC current, you will end up due to regulation, diode losses and so on, with a voltage about 1.25 * the AC rated voltage. So 71 * 1.25 = 88.7V and you are where you want. I got these figures from my own toroid supplier (Amplimo in the Netherlands), and they advised me the same as your supplier. For 12V secondaries, you should apply a factor of 1.1, 30V is 1.2, 100V is 1.25 and 230V is 1.35 the rated AC voltage. My suggestion is: Build your psu in a test-setup, apply the expected load as a DC resistor, and measure the voltage. Safest way to go. Don't worry about the caps; they will hold the high voltage for a while (but don't exaggerate). Good luck Bouke __________________ More Power Igor! More Power!
 22nd April 2005, 08:07 AM #12 bowdown   diyAudio Member   Join Date: Feb 2004 Location: Perth oh cheers Bakmeel i will give that a try and post my findings here in the next couple of days. Regards Bowdown
 16th May 2005, 01:16 PM #13 alexl   diyAudio Member   Join Date: Mar 2005 Location: canada Similar issue Hi, I'm building an amp using the Tripath chipset and I have a similar issue with the rail voltage being a bit higher than expected. I found that the main lines voltage at my place varies from 120 to 123,5V. Honestly, I expected to get 115V... I didn't checked before ordering the transformer. My mistake. It is a 1kVA, 45V dual secondary. With the transformer I have at 123,5V and under no load, I get 69V on the rails. I need to get something around 65V as the Tripath chipset must run under 70V and preferably not much higher than 65V. I found that I could lower the voltage a bit using a couple of diodes in series after the rectifier bridge to somewhere around 64-67 volts. Is this a good way to lower the voltage? I can't unwind the transformer as it is wrapped and filled with resin.
Kenshin
diyAudio Member

Join Date: Jan 2005
Location: China
Re: Similar issue

diodes have a forward voltage drop ~ 0.7V at big current.
but the voltage drop at very low current is smaller, it can be less than 0.2V.
So the method is not reliable.

try some regulation at DC output ? the voltage drop is low, so a linear regulation is enough.

Quote:
 Originally posted by alexl Hi, I'm building an amp using the Tripath chipset and I have a similar issue with the rail voltage being a bit higher than expected. I found that the main lines voltage at my place varies from 120 to 123,5V. Honestly, I expected to get 115V... I didn't checked before ordering the transformer. My mistake. It is a 1kVA, 45V dual secondary. With the transformer I have at 123,5V and under no load, I get 69V on the rails. I need to get something around 65V as the Tripath chipset must run under 70V and preferably not much higher than 65V. I found that I could lower the voltage a bit using a couple of diodes in series after the rectifier bridge to somewhere around 64-67 volts. Is this a good way to lower the voltage? I can't unwind the transformer as it is wrapped and filled with resin.

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