Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 7th November 2006, 11:02 PM   #1
zilog is offline zilog  Sweden
diyAudio Member
 
Join Date: Oct 2005
Default protecting mosfets in UcD

A few minutes ago I killed the output devices in my DIY UcD. They died during a swift burst of high output current (10-12A rms sine into resistive load), the mosfets being FDP3682. They often die for me during high power bursts, and I wonder what beside high Ids that might have killed them (I believe my deadtime still is on the high side, and the mosfets turn on slow). My gate drivers dont have any protection against negative or too high Vgs, should I add a zener of 15-20V and an antiparallel schottky to window Vgs?
  Reply With Quote
Old 8th November 2006, 04:00 PM   #2
RX5 is offline RX5  Philippines
diyAudio Member
 
RX5's Avatar
 
Join Date: Apr 2004
Location: TaC
I think there IS none... esp when your in the TWEAKING stage...

I have blown some FETs myself... even a solder shorting adjacent pcb tracks CAN kill ...

__________________
RoCk On!!! I love my diy UcD!!
  Reply With Quote
Old 11th November 2006, 05:47 AM   #3
MOER is offline MOER  United States
diyAudio Member
 
Join Date: Aug 2003
Location: SIMI VALLEY CA
Default FDP3682

Do not use these Mosfets as their tr at 46usec is slow. You need massive dead time and the addition of about 10 ohm gate resistors to protect them. Compare the tr of the IRFB4212 at 7.7usec or the STP14NF10 at 16usec and that is why these fets work much better.
  Reply With Quote
Old 11th November 2006, 06:34 AM   #4
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
Note that you can't make direct comparisons between switching times of different MOSFET because they are strongly dependent on the gate resistor chosen for the test and not all datasheets follow the same proportion of resistance to gate capacitance.

For example:

FDP3682 is rated with Rg=16 ohms for Cin=1250pF
STP14NF10 is rated with Rg=4.7ohms for Cin=400pF
IRFB4212 is rated with Rg=2.5ohms for Cin=550pF

The latter is obviously going to show the shortest times, and the former the longer. In my opinion the FDP is the most suited part for cass D and the STP the least (taking body diodes into account).
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 11th November 2006, 06:34 AM   #5
Baldin is offline Baldin  Denmark
diyAudio Member
 
Baldin's Avatar
 
Join Date: Jan 2005
Location: Copenhagen
Send a message via MSN to Baldin
It's 46 nano seconds (nS), and can't at all be considered as masive. Think these MOSFETs are ok for a class-d application. Don't think thats the problem.

Are you using a fast anti parallel diodes over DS on the fets? (like ES2D)
Are you using snubbers on the mosfets? (like the 10 Ohm-100pF in the app note)
I think that it could be caused by high spikes.

Is it running hot at idle?

Could it be the drivers not dilivering enough current at high output, and therefore not making a clean switching of the fets, causing through shoot?
__________________
Visit www.sensibleaudio.dk or read latest news on Baldin's Blog
  Reply With Quote
Old 11th November 2006, 04:15 PM   #6
RX5 is offline RX5  Philippines
diyAudio Member
 
RX5's Avatar
 
Join Date: Apr 2004
Location: TaC
Eva,

can you name -other- important parameters in choosing MOSFETs for Class D operation??

Im sure many would benefit from that....

Regards,
Raff
__________________
RoCk On!!! I love my diy UcD!!
  Reply With Quote
Old 12th November 2006, 05:41 AM   #7
MOER is offline MOER  United States
diyAudio Member
 
Join Date: Aug 2003
Location: SIMI VALLEY CA
Default FDP3682

Sorry about the typos nano secs is what I meant
  Reply With Quote
Old 12th November 2006, 01:51 PM   #8
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
Quote:
Originally posted by RX5
Eva,

can you name -other- important parameters in choosing MOSFETs for Class D operation??

Im sure many would benefit from that....

Regards,
Raff
Gate drive requirements (total gate charge), body diode reverse recovery charge (sometimes hard to compare due to different test conditions), body diode maximum recovery dV/dt (immediate failure when exceeded), conduction losses...
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 12th November 2006, 02:28 PM   #9
Banned
 
Join Date: Jan 2005
Hum i think thaty zilog have either gave up, lost internet or taken his life, because he havent logged in here since he posted this thread or been in the irc channel.
  Reply With Quote
Old 12th November 2006, 05:59 PM   #10
zilog is offline zilog  Sweden
diyAudio Member
 
Join Date: Oct 2005
Quote:
Originally posted by Tekko
Hum i think thaty zilog have either gave up, lost internet or taken his life, because he havent logged in here since he posted this thread or been in the irc channel.

Im at my parants, molding pieces of race faring for my motorcycle.
  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
Protecting a microcontroller rtarbell Parts 10 11th January 2008 01:23 AM
protecting a VR tube jarthel Tubes / Valves 14 10th May 2007 12:21 AM
why is my amp protecting? mbugua Class D 2 19th January 2007 12:58 PM
Protecting treble driver from DC? AndrewT Multi-Way 5 25th February 2006 03:33 PM
protecting my speakers from my GC damitamit Chip Amps 13 16th June 2003 03:46 PM


New To Site? Need Help?

All times are GMT. The time now is 06:18 PM.


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