FULL BRIDGE SMPS: With or without poly cap in primary coil? - 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 5th June 2009, 11:31 PM   #1
diyAudio Member
 
CHACALPOWERS's Avatar
 
Join Date: Jul 2007
Default FULL BRIDGE SMPS: With or without poly cap in primary coil?

Hi Dears
Exatly! This is my question for you:
In the FULL BRIDGE SMPS: Do I need to use the poly cap (1uF, 2u2,....400V) in primary coil?
This question is here because I see various SMPS FB projects with and without this cap.. (?)

Thak you very much

Sandro/CHACALPOWERS
  Reply With Quote
Old 6th June 2009, 12:40 AM   #2
TechGuy is offline TechGuy  United States
diyAudio Member
 
Join Date: Apr 2006
Location: Connecticut
The cap is used in Full bridge to prevent run away current flow if the transformer saturates. but the cap also has ESR, which increases the switch losses. The cap limits the amount of energy that can be transferred on each switching cycle. As the charge saturates in the capacitor the current input into the transformer drops. You may have to buy a large value Cap (or use multiple caps in parallel), if your output load is high and your core material limits your switching speed. If your output is drawing a heavy load the cap can increase output noise, because of a voltage drop on the secondary when the cap begins to saturate and limits input current to the transformer.

If you're concerned that your design may have bugs, you can also use a cap as safety training wheels to prevent blowing MOSFETS\IGBTs\FUSES ,if your controller fails to operate in the safe operating range.
  Reply With Quote
Old 6th June 2009, 01:01 AM   #3
diyAudio Member
 
CHACALPOWERS's Avatar
 
Join Date: Jul 2007
Default Great TechGuy

Mr. TechGuy

Ok, now I undestand because my 115/230VAC - 14.2VDC SMPS blowed very, so fast when I connected 0.15 ohms power resistor in output ...( ! )
Working with a 0.18 ohms power resistor in DC output (14.2V) no problem without the series cap, the IRFP460 mosfets (x4) units stay no warm, the output schotky diodes (Mospec S30D40C x 4 UNITS) no warm too, the IR2110 (02 UNITS) and SG3525 no problem, but, the core (toroid 4cm2 Ae) running in 57,45Khz stay some warm.
I 'll try build with, maybe 3u/400V poly cap to see the results.

Thank you very much by your comments.

Sandro from Brazil.
  Reply With Quote
Old 7th June 2009, 01:11 AM   #4
diyAudio Member
 
megajocke's Avatar
 
Join Date: Jan 2003
In a voltage mode supply fitting the capacitor is a very good idea.

In a peak current mode power supply on the other hand, a series capacitor must not be used.
  Reply With Quote
Old 9th June 2009, 02:55 PM   #5
diyAudio Member
 
darkfenriz's Avatar
 
Join Date: Jun 2004
Location: Warsaw
From your describtion it looks like you use a simple out of phase H-Bridge, don't you?
I suggest you used this capacitor then, for even RDSon differences may result in long-term DC saturation of transformer core.
A very long dead time helps though.

The case is different for phase-shift H-bridge, where you don't need that capacitor at all, aside from other benefits.
  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
Offline full-bridge SMPS....need help Nejc_car Power Supplies 1268 29th November 2014 08:19 PM
Primary DC blocking capacitor in a ZVT full bridge Design ? miversen Power Supplies 5 27th November 2008 03:03 AM
Full Bridge 90A SMPS... hawkfeather Power Supplies 11 20th December 2005 08:59 AM
Whats the difference between full bridge and half-bridge SMPS ? skaara Class D 6 3rd February 2005 08:23 PM


New To Site? Need Help?

All times are GMT. The time now is 10:52 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