100W mosfet amplifier with IRFP250 - Help!? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 20th July 2011, 07:12 AM   #1
radio is offline radio  Macedonia
Banned
 
Join Date: Oct 2009
Location: Bitola MACEDONIA
Angry 100W mosfet amplifier with IRFP250 - Help!?

Hello all!
I designed this amplifier under this schematics - circuit (see Figure 1).
By the time given to work around the amplifier output mosfet IRFP250 burn (churches) !?
Is someone can help and tell what the is problem ?!
Is someone can make a simulation of this amplifier?
What can I do to change the amplifier works without problems?
Thanks and cheers !
Attached Files
File Type: pdf Figure 1.(100W mosfet amplifier).pdf (77.3 KB, 767 views)

Last edited by radio; 20th July 2011 at 07:39 AM.
  Reply With Quote
Old 20th July 2011, 09:17 AM   #2
diyAudio Member
 
Join Date: Jun 2011
Do not install the fuses, instead fit 100 ohm 1 watt resistors in their place. These 'safety resistors' will limit current in the event of a fault and prevent the amplifier blowing up. Fuses will not act quick enough if there has been a build error.
Do not connect any input signal nor any load on the output.


Turn the bias preset potentiometer as far anti-clockwise as possible, do not force it. If you wish to set and check this prior to soldering it into the PCB, orient the preset potentiometer so that the middle pin is higher than the outer pins. Now measure the resistance between the middle pin and the rightmost pin, it should be less than 50 ohms. Connect an ammeter in series with the negative rail. Apply power and note the reading on the ammeter, it should be less than 20mA. The 'safety resistors' should also be cool. If either of these is not true, remove power immediately and check the bias preset potentiometer is wound to minimum. If it is then begin to look for solder bridges, broken tracks, dry joints and wrong components, etc.
If all seems OK then proceed to turn the bias preset potentiometer clockwise and you should see the current increase. Set it to 75mA then keep checking the current every minute to make sure it is not running away - it should not reach 100mA within 2 minutes, if it does then turn it down to 75mA again. There will be some movement whilst thermal equilibrium is reached so do not worry too much. Thermal equilibrium should be reached by about 15 minutes, depending on the heatsink. Do not attempt to connect a loudspeaker or play any signals as the 'safety resistors' will prevent the amplifier working in this way.
Once the bias current has been set you can check the output of the amp to make sure that the DC offset is less than 50mV. If it is more than 1V then there is a fault with the amplifier so check for solder bridges, broken tracks, dry joints and wrong components, etc.
Now that everything has been checked you can remove power and replace the 'safety resistors' with the correct rating fuses and re-check the bias procedure above (the bias current will raise a little due to no longer having resistors in the rails) then the amplifier is ready for use. It will not require further adjustment unless a different rail voltage is used or the heatsink is changed.
  Reply With Quote
Old 20th July 2011, 12:58 PM   #3
radio is offline radio  Macedonia
Banned
 
Join Date: Oct 2009
Location: Bitola MACEDONIA
Hi,
I set quiescent current to about 50mA. Amplifier worked well around 2 ... 3 hours, and then they burned the output transistors IRFP250?
It so happened twice and then I gave up ...
Amplifier has a problem i can not find it and fix, because we need help of experienced professionals!?
thanks
  Reply With Quote
Old 20th July 2011, 01:15 PM   #4
Banned
 
Join Date: Jan 2005
That looks like an old Elektor design, many of these had errors in them rendering them nonworking.
  Reply With Quote
Old 20th July 2011, 01:30 PM   #5
radio is offline radio  Macedonia
Banned
 
Join Date: Oct 2009
Location: Bitola MACEDONIA
Quote:
Originally Posted by Tekko View Post
That looks like an old Elektor design, many of these had errors in them rendering them nonworking.
Friends, because here on the forum asking for help to solve the problem!
Cheers
  Reply With Quote
Old 20th July 2011, 01:54 PM   #6
Banned
 
Join Date: Jan 2005
Look up quasi's thread "poweramp under developement. That circuit is tried and proven to work.
  Reply With Quote
Old 20th July 2011, 08:38 PM   #7
radio is offline radio  Macedonia
Banned
 
Join Date: Oct 2009
Location: Bitola MACEDONIA
Hi
If someone able do some simulation of this schematic (Figure 1) and see what went wrong !?
I do not dispose of such equipment to simulate?
For power suplly Us=+/-37Vdc!
Cheers

Last edited by radio; 20th July 2011 at 08:45 PM.
  Reply With Quote
Old 20th July 2011, 09:28 PM   #8
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Its not the worst design i have seen in fact similar to one of my old designs.
I found thermal runaway could be a problem so the Vbe needs to be on an output transistor or the heatsink at least.
Also I suspect you are gettingt oscillation on the output, put a 100pf from T7 collector to base.
These two fixes worked for me.
  Reply With Quote
Old 20th July 2011, 09:56 PM   #9
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
How interesting, the design appears to be a rip-off of my 160W n-channel MOSFET amp from my website. May I ask where you got it from?

The design does need the bias transistor T4 to be mounted on the main heatsink.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.

Last edited by richie00boy; 20th July 2011 at 09:59 PM.
  Reply With Quote
Old 21st July 2011, 12:08 AM   #10
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
R17, 18, 19 all need to be the same value, if T7 is going drive in symmetry with T6. But negative swings would be hurting for lack of bootstrap twice as soon as positive swings, is this why a symmetrical quasi was not used?

Last edited by kenpeter; 21st July 2011 at 12:23 AM.
  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
Maplin 100W mosfet amplifier - power supply problem HBrunt Solid State 32 3rd December 2013 08:11 AM
Good ~100W amplifier percy Solid State 16 3rd April 2013 06:16 PM
Tube/Mosfet 100W Hybrid Amplifier apexaudio Solid State 134 22nd June 2012 03:16 PM
100w amplifier blindmole Solid State 40 11th April 2011 10:25 PM
100w Mosfet amp m60gpmg Solid State 11 14th January 2004 08:48 PM


New To Site? Need Help?

All times are GMT. The time now is 06:55 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