200W class A psu considerations with IRF240
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
 29th December 2012, 07:50 PM #21 DUG   diyAudio Member   Join Date: Jan 2003 Location: mississauga ontario canada I have a question regarding the definition of CLASS A. Let's for the moment assume a complimentary/symmetry output stage with active devices in both the top and bottom positions. Let's assume +/- 16V rails and an 8R load. Let's also assume the device can go to rail just to make it easier. If my Iq is set to 0.1A and in a positive swing the peak current in the + side goes to 2A and the negative side is minimal. (lets say 0.001A) That would be class AB. If I set the Iq to 2.5A and had the same output swing and the bottom device maintained the 2.5A so the top device would have to supply 4.5A (2A o/p + 2.5A Iq from the bottom device) That would be class A because the bottom device was still in a conduction mode. What about in between. I set my Iq to 1A and design the circuitry to maintain that as a minimum. The positive swing goes to 16V @ 2A output. The upper device supplies 3A and the lower device still supplies 1A. This should also be class A...The inactive device (lower) is still maintaining conduction and has not "shut off". This definition seems to be in accordance with this thread: http://www.diyaudio.com/forums/solid...ion-class.html So if you have designed the output stage not to go below a certain current (never shut "off") then you have class A. Even on a 400W with only 0.5A Iq. This should make your class A power supply calculations easier. Thoughts anyone? __________________ Doug We are all learning...we can all help "You can't stop the signal, Mal. Everything goes somewhere..."
 29th December 2012, 11:31 PM #22 djk R.I.P     Join Date: Feb 2001 Location: USA 400W out of four Hexfets? Have you calculated the junction temperature? How will it look with a 55°C ambient temperature? __________________ Candidates for the Darwin Award should not read this author.
 9th July 2013, 04:45 AM #23 lovemov   diyAudio Member   Join Date: Nov 2003 Location: usa I doubt the calculation is correct? The calculation is based on 8ohm speaker, so what about 4ohm? For class A bias is fixed, so when change speaker from 8ohm to 4ohm, one gets half the watts output?
DUG
diyAudio Member

Join Date: Jan 2003
Quote:
 Originally Posted by lovemov I doubt the calculation is correct?...
Which calculation?

Quote:
 Originally Posted by lovemov ... The calculation is based on 8ohm speaker, so what about 4ohm? ...

Help me out here.

__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."

 9th July 2013, 09:49 PM #25 lovemov   diyAudio Member   Join Date: Nov 2003 Location: usa Many posts referring this: P = I^2*R or P = (I*2)^2*R. So I am wondering, if the bias 'I' (whatever it should be I or I*2) is constant, P will vary with R, which gets lower if R is lower, so 4ohm speaker gets 1/2 power of 8ohm...can't be right?
 10th July 2013, 12:47 AM #26 DUG   diyAudio Member   Join Date: Jan 2003 Location: mississauga ontario canada P = I^2*R or P = I*I*R That is what I learned...like what does work...like equivalent heating power. "P = (I*2)^2*R" came from a peak power calculation. rhythmsandy: "...( 3.6 x 2 )^2*8 = 414.72W peak and for continuous ... " (post #3) (I don't use that one personally) The power of 8R vs 4R would double (for 4R) assuming adequate supply of current with the same voltage applied to both 8R and 4R. The situation discussed was not this case. There was a limit to the current available. Goto go. __________________ Doug We are all learning...we can all help "You can't stop the signal, Mal. Everything goes somewhere..."
 10th July 2013, 01:15 PM #27 AudioSan   diyAudio Member   Join Date: Feb 2009 lovemov. the formula: (I*2)^2*R is class A power. and yes. without taking some action, the class A power will be half with half the impedance. however. in a push-pull design. it will leave class A and continue into class A/B for as long as the voltage allows it to. then the formula goes: p= V^/R lets say it can give full rail voltage, just to make it easy. +/-60V rails. 60*60/8ohm=450W peak/225W average. or. 60*0.707=42.4Vrms 42.4*42.4/8=225W at 4ohm, this will dobble. of course the PSU must manage the currents. and hold the voltage up at the same time. thats not likely to happend. Last edited by AudioSan; 10th July 2013 at 01:19 PM.

 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 Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post wengtech Elektor 7 17th May 2013 07:06 AM ljm_ljm Solid State 5 3rd October 2011 03:04 PM WTOAK33 Class D 6 19th July 2011 03:52 AM Session Class D 5 8th October 2009 07:08 PM lineup Solid State 28 25th November 2008 07:08 PM

 New To Site? Need Help?

All times are GMT. The time now is 03:01 PM.