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Old 23rd August 2008, 05:34 AM   #1
diyAudio Member
Join Date: Mar 2002
Location: n/a
Default Having trouble with F3 current source

Hey all.

I'm currently applying power to my F3 boards, and I'm having trouble setting the current source. I understand that the percentage is supposed to be the ratio of current through the output resistor to the ratio through the aleph resitors.

So what I've got, I measuring the AC voltage across resistors R6/R7/R8 (which make 0.4 ohm), and the output resistor R9 (0.47 ohm).

Here's what I get :

drop across r6/r7/r8 = 0.206 V
0.4 / 0.206 = 1.94 A

drop across r9 = 0.35 V
0.47 / 0.35 = 1.35 A

1.94/1.35 *100 = 140 % !!!!!!!!

That's not right ... No matter what I set P2 to, the current through the aleph resistors is alway greater than what's going though the output resistor.

Any idea where I may have gone wrong ?
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Old 23rd August 2008, 06:10 AM   #2
BDP is offline BDP  United States
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Join Date: Apr 2002
Location: SE Washington State
Should'nt the voltage drop across R6,7,8 be .66 volts, the emitter base junction of Q4?
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Old 23rd August 2008, 06:27 AM   #3
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Join Date: Mar 2002
Location: n/a
Sorry everyone.

Please delete this thread, or make it a sticky, as a permanent reminder of Ohm's law.

My calcs should have been along the lines of 0.204 (V)/0.4 (ohms), rather than 0.4 / .204 .....

*smacks head*
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