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Lateral Mosfets Double Die TO-3 ESP P101
Lateral Mosfets Double Die TO-3 ESP P101
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Old 11th September 2018, 08:17 PM   #1
a1095us is offline a1095us  United States
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Default Lateral Mosfets Double Die TO-3 ESP P101

I want to build a mosfet amplifier (maybe the ESP P101) utilizing the transformer and heatsink assembly from a retired Tandberg 3012 integrated amp. The Tandberg was rated at 100W rms at 8 ohms / Ch.
The transformer secondary supplies about 57VDC +/- after smoothing to the rails. The original heatsink was quite robust with one pair of complementary mosfet outputs per channel. The original outputs were 2sj55 and 2sk175 rated at (ID) 8A and 125W ea. Tandberg seemed to think that these ratings were adequate for the 57V rails and functioned till the end without failure. Rod Elliot (ESP) seems to take a much more conservative approach with these higher rails (57V) and strongly suggests doubling up on the complementary pairs. As you can see in the pic the Tandberg heatsink assy. provides only for 2 TO-3 outputs per channel.
ESP P101 amplifier.
Rod recommends the Exicon ECX10N20 and ECX10P20 for the low power output. For my application (at the higher rail) I am considering the Exicon double die TO-3 versions, ECF20N20 and ECF20P20. I have read the pros and cons about the double die versions and still wonder if there are valid points to not using them. If itís on the internet, it must be valid!?
Can I basically use the double die versions to replace the dual complementary lateral outputs without any real change to the P101 driver circuit at +/- 57VDC.
I emailed Rod and did not get a response.
ORÖ should I take the chance and use the lower power rated Exicons and justify it by what Tandberg used for power rated outputs. Seems to me that if this amp is used well below its rated output (like in my apartment), I should be able to get away with using the lower rated lateral outputs.
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Old 11th September 2018, 08:26 PM   #2
Bensen is offline Bensen  Belgium
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Hi,

When checking the esp website. The high power version of project 101 already uses two pairs of latfet's for the OPS. Wy do you think using 1pair of double die's should be a problem?
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Old 11th September 2018, 09:25 PM   #3
a1095us is offline a1095us  United States
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Frankly I don't! Just read some posts, not just on this forum, relating to double dies not sounding as good as regular laterals (don't see how?) and also issue with power dissipation vs. two regular doubled up. Higher capacitance?
Maybe this post is a non-issue. Just putting it out there!
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Old 12th September 2018, 03:00 AM   #4
fab is online now fab  Canada
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Lateral Mosfets Double Die TO-3 ESP P101
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Originally Posted by a1095us View Post
Frankly I don't! Just read some posts, not just on this forum, relating to double dies not sounding as good as regular laterals (don't see how?) and also issue with power dissipation vs. two regular doubled up. Higher capacitance?
Maybe this post is a non-issue. Just putting it out there!
This seems to be non-sense for sound. Also, double-die Mosfet has the same capacitance as 2 single Mosfet in parallel. However, double die has the best matching between the 2 dies. For dissipation, double die has a bigger package than single and you simply need good heatsinks and good thermal contact.
Good luck
Fab
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Old 12th September 2018, 05:07 AM   #5
BesPav is offline BesPav  Russian Federation
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Quote:
Originally Posted by a1095us View Post
The Tandberg was rated at 100W rms at 8 ohms / Ch. The transformer secondary supplies about 57VDC +/- after smoothing to the rails.
Twice as high rails for rated RMS power. Or power was limited by dissipation (sad, because user doesnít know about). Or bad utilizing of supply voltage(what about best schemotechnic approaches).

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I have read the pros and cons about the double die versions and still wonder if there are valid points to not using them.
The main cons is a relatively smaller thermal contact point, so try not to drive them hard.

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Can I basically use the double die versions to replace the dual complementary lateral outputs without any real change to the P101 driver circuit at +/- 57VDC.
Remember worst case for reactive load:
SOA BJT specialists wanted
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Old 12th September 2018, 02:50 PM   #6
alexberg is offline alexberg
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Lateral FETs are much more robust than HEXFET or vertical DMOSFET like IRF240 and can sustain quite a lot of abuse unless the total dissipation is exceeded. Yet another factor lowering lifetime of a FET is gate-source overload which is not the case.
Second of all specs are about the same except the transconductance which may or may not contribute to distortions, biasing etc.
Thirdly, thermal interface material impedes heat transfer, a lot. So using two TO-3 instead of the one is advantageous indeed (but pricey). Metal can costs more than die itself.
Fourthly class B ideal efficiency is Pi/4 so you are kida safe with 4*125W (or 2*250w) at ideal heatsink trying to squeese the whole 100W.
Fifthly. Safe operating area or SOA. BJTs were really bad on this but not fets. Let's see.
Assuming no voltage sag of DC bus we'll get 57V/(8+1)=6A peak, where 8 Ohm is the load and 1 Ohm is Rds. Let's say inductive load and you are getting full voltage (i.e. 57 VDC) across the fet and max current (i.e. 6A) with Pi/4 phase shift between the former and the latter. This yields 342/2=171 W of instantaneous power. Safe again.
Despite #4 post double die package is the very same i.e. TO-3 so third assertion stays.
Same batch devices are usually indistinguishable but if you want to match fets look for threshold voltage first. +/-50 mV will do. That's said you get equal current sharing during transitions which is much more important than static.
Cheers

Last edited by alexberg; 12th September 2018 at 02:59 PM.
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Old 12th September 2018, 03:07 PM   #7
fab is online now fab  Canada
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Lateral Mosfets Double Die TO-3 ESP P101
Exicon ECW20N20 or Alfet equivalent is to-264 package and not to-3p. Of course, the difference is not drastic but still is bigger with to-264.
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Old 12th September 2018, 05:00 PM   #8
alexberg is offline alexberg
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Quote:
Originally Posted by fab View Post
Exicon ECW20N20 or Alfet equivalent is to-264 package and not to-3p. Of course, the difference is not drastic but still is bigger with to-264.
Fab
The devices mentioned by topic starter are in to-3 metal can package as well as the heatsink drilling is for. Plastic ones like 247/264 have, despite copper vs special tempco alloy in TO-3, exactly the same power rating. It well might be that die itself is the limiting factor in total power dissipation being, for instance, of a substantial thickness. But most pads are worse than metal so the higher the area the heat is transferred through the less thermal resistance will be.
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Old 12th September 2018, 05:50 PM   #9
fab is online now fab  Canada
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Lateral Mosfets Double Die TO-3 ESP P101
Sorry I had not considered the existence of double die lateral mister in to-3 metal package.
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Old 13th September 2018, 02:30 PM   #10
a1095us is offline a1095us  United States
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Thanks for the input... all! No need to drag this out. I've decided to order the TO-3 double die versions and the P101 boards form Rod.
This will replace an aging, but going strong, Bryston 3BST. Hope it sounds as good or better. Will report back when project completed.
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