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16th December 2002, 11:18 PM  #1 
diyAudio Member

Max current consumption for P3A?
how can i calculate the max. current required for the p3a when
outputing 100watt into 4ohm load, using +35/35 volt. PS.? isit using the simple formula ( so 100/35 = 2.8A !!) i dont think so.. so any help?! 
16th December 2002, 11:28 PM  #2 
diyAudio Member
Join Date: Jan 2002
Location: Borås, Sweden, Tellus


17th December 2002, 01:37 PM  #3  
diyAudio Member

Quote:
if anybody knows it so why not to write it down direct? 

19th December 2002, 05:31 PM  #4 
diyAudio Member

ballpark figure
do you already have a power supply? Why do you need the max current?
I would estimate it at around 4.5 amps. 35V rails into 4 ohm load is the max that Rod recomends. That current draw is surprisingly close to the 5 amp fuses he uses on the rails. If you are using 35V rails, I think you will have a little more than 100W also. Austin 
19th December 2002, 05:50 PM  #5 
diyAudio Member
Join Date: Dec 2001
Location: Pittsburgh, PA, USA

Well, 353=32Vpeak, 22.6Vrms. P=V^2/R gives 128W.
Ipeak=8A, Irms=5.65A Of course, each half of the supply only supplies current for half a cycle (+bias current for other half) so the RMS current seen by each half of the supply is roughly 2.8A + (bias current)/2 So, you were pretty close to begin with. You will probably never have to supply close to this much current continuously, given the crest factor of music. However, if you overdrive (square wave) your current is double the calculation for a since wave. I hope your output devices are robust. 
20th December 2002, 02:51 PM  #6  
diyAudio Member

Quote:
but whats the bias current?! i know its v.basic stuff but forgive me i dont ve much knowledge about the transistors and its related dif. .. thanks again. 

20th December 2002, 03:11 PM  #7 
diyAudio Member
Join Date: Dec 2001
Location: Pittsburgh, PA, USA

The bias current is current that is always flowing regardless of the demand. If you've followed Rod's instructions, you've adjusted the bias current to 100mA, which is pretty negligable in this calculation. Some people will bias the supply much higher, in which case it makes more of a difference.

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