Fqa12p20 Fqa19n20c Discontinuation

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#50
> TO-220 is maybe good for up to 2 W continous or so.

This statement is IMHO misleading to say the least.

The datasheets of both devices actually quoted the thermal resistance junction to case.
For the FQP19N20C (metal tag), it is 0.9 degC/W.
For the FQP12P20 it is 1.04 degC/W.

These values are much better than the average TO220 devices and are actually better than some TO247 ot TO3P devices.
e.g. 2SK1058 is TO3P but has a Rthjc of 1.25 degC/W.
2SK214 is TO220 and has a Rthjc of 4.16 degC/W.
D44H11 is TO220 and has a Rthjc of 1.8 degC/W.

So too dangerous to generalise using package type only, without looking into the details.

If you use my design criteria as detailed in my Linear Audio article :
http://www.linearaudio.net/images/stories/Didden LA V3 PK lr.pdf
(Free download, thanks to generosity of Jan Didden)

you can assume a heatsink temperature of 65degC, and a substrate temperature of 100degC. Then you can dissipate 30W safely, again IMHO.
In any case much more than 2W.


Patrick
 
#55
I recently paired up the Vishay IRFP240 with some IRFP9240 and 9140 from IR, all the devices were from different times of purchase.

Case 1: F5 Turbo with IR IRFP9240 and Vishay IRFP240, worked very well. Surprisingly well. The Ir parts were not and will not match. The Vishay parts matched up well. This change was done in one channel which was not showing proper current sharing on the negative supply. Sounds identical to the other channel.

Case 2: Juma's F5 with BJT input, IR IRFP9140 and Vishay IRFP240, sounded terrible and am now in the process of obtaining P-gender parts from Vishay.

My initial IR 240/9240 parts were produced from a known faker on eBay (before he was known to be a faker). They match horribly but work all right. To fix this for my 'Epic F5T' build (in the works since 2012), I procured parts locally, and got the Vishay IRFP240 and IRFP9140, which I assumed would be fine.

They are not.

To their credit, the Vishay parts match superbly. Of the 12 I got all were within a 10% range. The IR9140 have much bigger swings, but I still managed 8 decent pair matches for the 4 amp modules. I needed to deploy some of the unmatched ones when one channel of another implementation blew (single devices), and the results were not pretty. There are big differences in sound from the other channel, and when I replaced that one as well, it just sounded plain bad.

I will be taking measurements to see how bad the degradation is, but I suppose that all of these choices come with caveats.
 
#56
Assuming that there is not some other problem, the issue of sound with the
240 / 9240 's is that traditionally the IR version of the P channel part
suffered from the frequency-shelving characteristic of the transconductance,
which looks a lot like the baffle-step correction used in some loudspeaker
systems. It imparts some alteration of characteristic from low to high
frequencies (for good or bad).

Not all the IRF9XXX parts have this - Harris didn't, and most Samsung did not,
and I'm not sure what the future holds for the IR parts now under Vishay.

Traditionally the Toshiba parts seem to have been the ones to beat, but they
seem to have been discontinued. Fairchild makes similar parts, you just
want to watch the higher temperature coefficients.

In general though, "complementary" power Mosfets with the appropriate
voltage, current and wattage ratings will work satisfactorily, that is to say
that they should not sound "just plain bad". There may be other problems
in this case.

😎
 
#58
Nelson Pass said:
In general though, "complementary" power Mosfets with the appropriate
voltage, current and wattage ratings will work satisfactorily, that is to say
that they should not sound "just plain bad". There may be other problems
in this case.

😎
Click to expand...

🙂

Thanks so much Nelson, great to hear your take on this. It is a fairly different circuit where I experienced the degradation, the front end uses BJTs and feedback capacitors instead of the 170/74 devices.

I shall investigate further, I am sure there must be a logical explanation for the issues I had. The Fairchild parts sounded great in the original F5, and the IR parts also sounded very good even when mixed with the Vishays in the traditional F5T circuit. This is an aberration, but hopefully it is something else in the circuit at the root of this.

Thanks again!
 
#60
sangram said:
... Case 2: Juma's F5 with BJT input, IR IRFP9140 and Vishay IRFP240, sounded terrible ...
Click to expand...
Please don't put my name on that circuit like that.
You changed it a lot, trying to be creative without really understanding how it works. So it's your incompetent adaptaion of the circuit and build with inferior parts that gave you bad results and it's only fair to mention that.
 
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