I would think reliability is an issue with switching supplies. Too many parts. I imagine if this was a good idea for Class A amps then the master would be doing it already.
It would be nice to get Nelson's comments on this.
If all things are considered and Nelson says it is a complete waste of time.
I will forget about it.
If all things are considered and Nelson says it is a complete waste of time.
I will forget about it.
I don't think it's a waste of time at all. My take on it is
that if you use it, some sort of good passive filtering is
probably a good idea.
Maybe I'll buy a pair of those nice open switchers and try it.
😎
that if you use it, some sort of good passive filtering is
probably a good idea.
Maybe I'll buy a pair of those nice open switchers and try it.
😎
Tomorrow I am going to do some noise measurements on my switch mode powered B1 buffer before and after the rc filtering, to see what the difference is.
I'm only to page 222, so sorry if I havent got there yet, but was wondering what everyone is going to do now that FQA19N20C and FQA12P20 are discontinued? I ordered a parts kit from Tech-DIY, but was wondering if there is a replacement?
Thanks, back to the thread,'
Russellc
Thanks, back to the thread,'
Russellc
Matching
Speaking of the Fairchild parts...
I was looking at the threshold voltage of the FQA12P20 vs the FQA19N20C and
noticed there is about a 1V difference. That wasn't the case with the original
MOSFETs. When you adjust the bias to get 1.3A one pot will be higher than the
other. Doesn't that make the gain on one side of the input fets higher than the
other? Does that make any difference or does the feedback take care of it?
I also noticed on one of the pictures from an F5 review that a 2.2 ohm resistor
was put in parallel with the 0.47 ohm resistor on the N-Channel side. Does this
have anything to do with the difference?
P.S. I haven't matched anything and the output on an oscilloscope looks very
symmetric. I just don't understand why.🙁
Thanks.
Speaking of the Fairchild parts...
I was looking at the threshold voltage of the FQA12P20 vs the FQA19N20C and
noticed there is about a 1V difference. That wasn't the case with the original
MOSFETs. When you adjust the bias to get 1.3A one pot will be higher than the
other. Doesn't that make the gain on one side of the input fets higher than the
other? Does that make any difference or does the feedback take care of it?
I also noticed on one of the pictures from an F5 review that a 2.2 ohm resistor
was put in parallel with the 0.47 ohm resistor on the N-Channel side. Does this
have anything to do with the difference?
P.S. I haven't matched anything and the output on an oscilloscope looks very
symmetric. I just don't understand why.🙁
Thanks.
Thanks for the reply. I ordered the kits from Tech-Diy with the IRF devices, and also ordered 2 pairs of the Fairchild devices, so I should be covered.
Russellc
Yes I will.
I will try everything. Switch mode is more interesting to me though, mainly because of the hatred people have toward it.
I love the underdog.
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You obviously didn't read the whole thread. The issues that you mention are already discussed at length (in some other threads too).
Russel, the Tech-diy kits are avaiable with the Fairchild FQA12P20 and FQA19N20C MOSFET's. I received these within the last couple of weeks.
Attachments
While I'm in the posting mode, a quick question, if I might. I have the Cviller boards and at looking at the location of the LED through holes I noticed resistor #35 location. Is this the location of the resistor for the LED ?
Actually I have read most of the thread and don't remember any mention of my
specific questions. How about giving me post numbers or just a short answer. I
have read quite a bit about the lack of need for matching, but not why.