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27th November 2009, 12:31 AM  #1 
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Ratio of power into load and driver transistor
I have just wrote a small program to work out the ratio of the load power to to the output transistor power.
I was previously told it was 60% in load to 40% in transistor. Clearly at half rail volts the speaker and output transistor dissipate teh same power. However towards each rail the power in the transistor goes towards zero. I was wondering if anyone could verify my program and calculations for a full cycle? loadpower=0; tranpower = 0; bplus = 60; //60 volts bplus rail for (cx = 0; cx <= 360; cx++) { ///////////////// //calc power into load ///////////////// ax = (sindx(cx) * bplus)/256; //get voltage across load ax = abs(ax); //only work with +ve voltages else cancels to zero loadpower = loadpower+((ax*ax)/4) ; //volts sqred div 4ohms /////////////////////////// //calc power in transistor /////////////////////////// bx = (sindx(cx) * bplus) / 256; //get voltage across load bx = abs(bx); bx = bx / 4; //div by 4 ohms to get current through load dx = (sindx(cx) * bplus) / 256; //get voltage across load dx = bplusabs(dx); //bplus  volts across load = volts across transistor //get power in transistor tranpower = tranpower+(dx * bx); //v * i } System.Windows.MessageBox.Show("Load power=" + Convert.ToString(loadpower)); System.Windows.MessageBox.Show("Transistor power=" + Convert.ToString(tranpower));
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27th November 2009, 12:58 AM  #2 
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For.a.4.ohm.load.and.60.volt.b+
Applied.sine.wave.peak.voltage....power.in.transis tor....power.in.speaker. 60..........................................116... .....................439 50..........................................154... .....................304 40..........................................166... .....................193 30..........................................156... .....................107 20..........................................116... .....................46 10..........................................60.... ......................10 It can be seen that there is more power in the transistor at around a 30 volt sine wave than on 60 volt sine wave.
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27th November 2009, 12:59 PM  #3 
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Congratulations: you have just reinvented the wheel (sort of):
http://www.phy.auckland.ac.nz/Staff/...amplifiers.pdf 
27th November 2009, 02:07 PM  #4 
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Location: massachusetts

Your numbers are in the right ballpark, but seem off. I'm not familiar with the program language, but it looks you should be diding your steps by 360, not 256. RMS voltage should be .6366 times peak voltage, which would give you a power of 357 watts into a 4 ohm load, and 89.25 at 30 volts peak.
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27th November 2009, 08:15 PM  #5  
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Quote:
Your absolutely right I should divide by 360 because there are 360 samples taken which is just the same as integrating. I have now added a div 360 on my program and it makes much more sense now.
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27th November 2009, 08:17 PM  #6  
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Quote:
It was interesting to do because I also added another variable for the amplitude of the sine wave so I could try different amplitude sines with different b+ rails.
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27th November 2009, 11:12 PM  #7 
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Join Date: Apr 2008
Location: Carlisle, England

It can be seen that most power gets dissipated into the heatsink at 2/3rd peak volts.
Applied sine voltsspeaker WDriver W Voltage=0 Loadpower=0 Tranpower=0 Voltage=1 Loadpower=0 Tranpower=0 Voltage=2 Loadpower=0 Tranpower=0 Voltage=3 Loadpower=0 Tranpower=0 Voltage=4 Loadpower=1 Tranpower=0 Voltage=5 Loadpower=2 Tranpower=23 Voltage=6 Loadpower=3 Tranpower=29 Voltage=7 Loadpower=4 Tranpower=33 Voltage=8 Loadpower=6 Tranpower=36 Voltage=9 Loadpower=8 Tranpower=53 Voltage=10 Loadpower=10 Tranpower=60 Voltage=11 Loadpower=13 Tranpower=64 Voltage=12 Loadpower=15 Tranpower=67 Voltage=13 Loadpower=18 Tranpower=80 Voltage=14 Loadpower=22 Tranpower=87 Voltage=15 Loadpower=25 Tranpower=91 Voltage=16 Loadpower=29 Tranpower=94 Voltage=17 Loadpower=33 Tranpower=105 Voltage=18 Loadpower=37 Tranpower=110 Voltage=19 Loadpower=41 Tranpower=113 Voltage=20 Loadpower=46 Tranpower=116 Voltage=21 Loadpower=51 Tranpower=125 Voltage=22 Loadpower=56 Tranpower=129 Voltage=23 Loadpower=62 Tranpower=132 Voltage=24 Loadpower=67 Tranpower=134 Voltage=25 Loadpower=74 Tranpower=142 Voltage=26 Loadpower=80 Tranpower=145 Voltage=27 Loadpower=86 Tranpower=147 Voltage=28 Loadpower=93 Tranpower=149 Voltage=29 Loadpower=100 Tranpower=154 Voltage=30 Loadpower=107 Tranpower=157 Voltage=31 Loadpower=114 Tranpower=157 Voltage=32 Loadpower=123 Tranpower=159 Voltage=33 Loadpower=130 Tranpower=162 Voltage=34 Loadpower=139 Tranpower=165 Voltage=35 Loadpower=147 Tranpower=164 Voltage=36 Loadpower=155 Tranpower=165 Voltage=37 Loadpower=165 Tranpower=167 Voltage=38 Loadpower=174 Tranpower=168 Voltage=39 Loadpower=183 Tranpower=167 Voltage=40 Loadpower=193 Tranpower=167 Voltage=41 Loadpower=203 Tranpower=168 Voltage=42 Loadpower=214 Tranpower=167 Voltage=43 Loadpower=224 Tranpower=166 Voltage=44 Loadpower=235 Tranpower=164 Voltage=45 Loadpower=246 Tranpower=164 Voltage=46 Loadpower=257 Tranpower=162 Voltage=47 Loadpower=268 Tranpower=161 Voltage=48 Loadpower=280 Tranpower=159 Voltage=49 Loadpower=292 Tranpower=157 Voltage=50 Loadpower=305 Tranpower=155 Voltage=51 Loadpower=318 Tranpower=151 Voltage=52 Loadpower=329 Tranpower=148 Voltage=53 Loadpower=342 Tranpower=145 Voltage=54 Loadpower=355 Tranpower=143 Voltage=55 Loadpower=369 Tranpower=138 Voltage=56 Loadpower=384 Tranpower=134 Voltage=57 Loadpower=397 Tranpower=130 Voltage=58 Loadpower=411 Tranpower=126 Voltage=59 Loadpower=425 Tranpower=121 Voltage=60 Loadpower=440 Tranpower=116
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28th November 2009, 08:08 AM  #8  
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