Choosing diode Vrrm in a power supply - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th December 2008, 08:50 PM   #1
diyAudio Member
 
Join Date: Jun 2008
Location: Romania
Question Choosing diode Vrrm in a power supply

I was reading an article on power supplies by Rod Elliott when something caught my attention. He basically says that diodes used in a full-wave center tapped rectifier must have a Vrrm higher than twice the peak of AC voltage, even giving an example where rectifying 25-0-25 volts of AC you need diodes rated for 200V reverse voltage.

That would mean that I need at least 300Vrrm diodes in the power supplies that I use for my ESP P101 amps as I have a 50-0-50 V transformer (around 140 volts peak, double that as stated by Rod), but I had already used BY229-200 (200Vrrm), later replaced with MBR40250 Schottkys (250Vrrm) with no ill effects... Am I pushing these diodes far beyond their specs or is there a mistake in Rod's article? (I for one cannot see a moment when a diode is reverse-biased with more than 140V)

Here it is, for reference (check the "Rectifier Diodes" paragraph):
http://sound.westhost.com/power-supplies.htm
  Reply With Quote
Old 15th December 2008, 08:45 PM   #2
dtproff is offline dtproff  United States
diyAudio Member
 
Join Date: Oct 2008
Location: Plano, TX, USA
For a 60Hz transformer I use the following.

Vfd=Forward Voltage Drop of the output rectifier Diode
Vs= Secondary Side Vac RMS Voltage on the Transformer
Vrr=Reverse voltage on the rectifier.
The 1.18 multiplier compensates for the difference between the nominal line voltage and the maximum line voltage the AC mains should see.

The Sqrt(2) term gives you the peak voltage of a sin wave.

The 2* multipliier is the voltage seen across a diode when the transformer winding is full negative related to the center tap.

The 1.2 term derates the Diode by 20% for safety margin.

(2*(Vs*1.18*Sqrt(2))+Vfd)*1.2=Vrr

So a 25-0-25 venter tapped transformer output winding would need a 102V rectifier for a sin wave transformer. You could use a 100V diode if you had too but I would probably use a 150V diode just to make sure I had margin.

For a PWM controller such as a flyback then then the equation is different since you have to account for the leakage inductance spike and differences in the duty cycle of the PWQM signal.

I hope this helps.

Tony
  Reply With Quote
Old 15th December 2008, 09:54 PM   #3
diyAudio Member
 
Join Date: Jun 2008
Location: Romania
Thanks for your answer. That's exactly how I thought, but for some reason Rod says the diodes should have double the Vrr...

Quote:
In the case of a dual supply (using a 25-0-25V transformer), the worst case peak AC voltage is 80V, so the diodes must be rated at 200V PIV.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
40A 250V Schottky Power Diodes- Has anyone use in Power Amp to replace Diode Bridge? dtm1962 Solid State 10 15th September 2011 07:38 PM
hybrid power supply: diode bridge into diode tube engels Tubes / Valves 8 24th September 2007 09:18 AM
single Diode power supply? robertc Tubes / Valves 8 9th November 2006 08:26 AM
Two diode split supply? Skorpio Power Supplies 4 17th April 2006 10:12 AM
Single diode supply for DAC fedde Digital Source 25 14th July 2005 08:41 PM


New To Site? Need Help?

All times are GMT. The time now is 10:19 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2