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 9th June 2009, 05:16 PM #451 Gyuri   diyAudio Member     Join Date: Nov 2003 Location: Budapest This is perfect according to my opinion! http://ugowlw.bay.livefilestore.com/...C_00980001.JPG Gyuri __________________ Those who would have deserved the life they are all dead already. "Oh, my dead dears!" - Captain Cat
 10th June 2009, 08:53 PM #452 luvdunhill   diyAudio Member     Join Date: Jul 2006 I have a quick question for the masters of off-topic. My question is about the second graph on this Datasheet I have 30V bench supply and a resistor to source 150mA of current. Since Vds = Vgs when testing (according to the Zenv3 documentation) and this value ranges from 3.20V to 3.55V depending on the sample. Ambient temperature is 60C for all samples and the devices are not heatsinked, but enclosed in a box with a probe to verify when 60C is reached to take the Vgs reading. I don't know if anyone has done things this way, but it seems to be very repeatable. Anyways, back to my quesiton... the second graph is at 25C and it looks like if we take the 3.50V for Vds = Vgs there should be 233mA of current. Would this value drop this much because of the case temperature? I just wanted to see if I was in the right ball park. The compliments are about 1V less Vds on average (same voltage and current) and I can almost convince myself of this looking at the Datasheet At Vds = Vgs = 2V for example, the Nch says ~180mA @ 25C and the Pch says 100mA @ 25C. I'm not sure how to do some calculations to see if this difference would result in approximately 1V lower Vds I see for the Nch, is this possible?
 10th June 2009, 09:28 PM #453 Nelson Pass   The one and only     Join Date: Mar 2001 Graph #4 looks to show about a 30% or so drop in Vgs over that temperature range, so it appears reasonable.
luvdunhill
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Join Date: Jul 2006
Quote:
 Originally posted by Nelson Pass Graph #4 looks to show about a 30% or so drop in Vgs over that temperature range, so it appears reasonable.
excellent! This makes since.

One more question. When paralleling MOSFETs, how do you determine the best value of the ballast resistor? I have four of each polarity of these paralleled with 2 ohm ballast resistors (sorta like F4 output stage), with the MOSFETs chosen at random. Now I've matched them to Vds 0.01V or so. Is this a case where one needs to be able to measure distortion? Could I just lower the values until the voltage drop across the resistors isn't equal? Is there somewhere I could read some more on this perhaps?

 26th June 2009, 04:30 PM #455 luvdunhill   diyAudio Member     Join Date: Jul 2006 ok, so let me try again Starting with the F5, the resistors in the output stage are 0.47R and the voltage drop is 0.6V. 3W resistors are speced and this is roughly 4 times the power at quiescent current. Now, with the F4, the resistors are 0.47R and voltage drop is 0.25V and 3W resistors are used. So, in the case of F4, why not cut the 0.47R value in half, assuming well-matched devices, and you could parallel two 0.47R resistors together to get the lower value? At what point does it make sense to stop lowering this value, at the point where the voltage drop across this resistor varies by a certain amount, due to matching becoming increasingly important as this value decreases? Is 4x the power at quiescent current used in the F5 a good rule of thumb to size output resistors?
 26th June 2009, 07:50 PM #456 Nelson Pass   The one and only     Join Date: Mar 2001 Usually it's a matter of what class the OS will operate in, what damping factor you want, and how much thermal stability you need. As a simple rule, you want the lowest values that are consistent with good current sharing (matching) and thermal stability. 0.47 ohms is a convenient figure, but it can easily range from 0.1 to 1.0 per device.
 26th June 2009, 10:49 PM #457 R-K Rønningstad   diyAudio Member     Join Date: Jan 2006 Location: Oslo Seems it is N.P.'s birthday. Congratulations Nelson! All the best RK
steenoe
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Quote:
 Originally posted by R-K Rønningstad Seems it is N.P.'s birthday. Congratulations Nelson! All the best RK
Seems like the most exciting fact, that this forum can come up with

 4th July 2009, 12:23 AM #459 Nelson Pass   The one and only     Join Date: Mar 2001 Works for me.
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Re: NEW FORUM FOR ALL FORMER YU DiyAs

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 Originally posted by Zen Mod re-post from Texas ......... wait - not from there ...... from Introductions :

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