200W MOSFET CFA amp

[dadod]

Originally Posted by Krisfr

Are LTSpice models available for all of these from Renesas or ?

I think they are very similar and could be used in place of Hitachi, so simulation with Hitachi is good enough.

[s2udio]

Why not use Exicon 1020 power fets in the output stage.
And looks far over complicated...most will disagree I am sure .

[ilimzn]

Renesas = new name of the semiconductor division of Hitachi.
J162/K1056 are actually J50/K135 in TO-3P like cases.
Exicon/Magnetec/Alfet are apparently all made in the same fab and are based on Hitachi J56/K176. Exicon parts are direct drop-in replacements, however Exicon offers selection by treshold (color dot marking) which is useful when paralleling the MOSFETs. In fact, there is some advantage in omitting source resistors in favor of selecting MOSFETs to parallel. Among other things, source is on the case so you can simply put all of them on the same heatsink without isolation, and use it as the output terminal, isolating the heatsink itself, which is actually best done by using a mounting profile (usually an aluminium L or T profile) for the MOSFETs and isolating this profile from the heatsink. The total thermal resistance ends up being lower on account of the larger mating surface between profile and heatsink, compared to the sum of mating surfaces between the transistors and the profile.
It should be noted that it's fairly simple to find marching N-ch laterals, not so simple with P-ch (one needs about 3-4 times as many P-ch MOSFETs to chose from to get the same number of close matches, as for N-ch).
Source resistors will improve matching at lower currents but the voltage drop across them is far to low to make a difference at high currents due to the relatively low Gm of the laterals. The models do not show that in the real world they can vary quite a bit. It's gotten better with the newer production parts (J162/K1056), but not drastically so, especially concerning the P-ch part. When laterals were first introduced a number of manufacturers used them in their designs, strating with Hitachi themselves, but there were also Kyocera, Sanyo, and a ton of PA amp manufacturers. In the HiFi realm, it's quite conspicuous that most amps were of fairly low power in order to use a single pair. Amps that used multiple pairs invariably had matched parts (at least as far as i can tell from experience with Hitachi, Kyocera, Sanyo, Strasser, and a numer of other manufacturer's amps).

[DUG]

Just a few questions/comments

R46/R47 not symmetrical?

No equivalent for R63 on negative side?

FET gate resistors...220R in positive side and 150R in negative side.

Output quiescent current not adjustable?

[Walkalone]

2SC/KSC3503 & 2SA/KSA1381 with ''C'' rank Hfe are not available.
Mouser & Digikey current have ''E'' for 2SA/KSA and ''D'' for 2SC/KSC.

[Bonsai]

Good distortion results and slew rate on your design dadod. I think this clearly demonstrates the role in a CFA that the feedback resistor plays in setting the amplifier gm - you are getting these good results because there is plenty of feedback at HF, but you are able to curtail it at HF with TPC and avoid running into phase shift problems due to the output stage - FET's no doubt allowing this as well.

[dadod]

Originally Posted by ilimzn

Renesas = new name of the semiconductor division of Hitachi.
J162/K1056 are actually J50/K135 in TO-3P like cases.
Exicon/Magnetec/Alfet are apparently all made in the same fab and are based on Hitachi J56/K176. Exicon parts are direct drop-in replacements, however Exicon offers selection by treshold (color dot marking) which is useful when paralleling the MOSFETs. In fact, there is some advantage in omitting source resistors in favor of selecting MOSFETs to parallel. Among other things, source is on the case so you can simply put all of them on the same heatsink without isolation, and use it as the output terminal, isolating the heatsink itself, which is actually best done by using a mounting profile (usually an aluminium L or T profile) for the MOSFETs and isolating this profile from the heatsink. The total thermal resistance ends up being lower on account of the larger mating surface between profile and heatsink, compared to the sum of mating surfaces between the transistors and the profile.
It should be noted that it's fairly simple to find marching N-ch laterals, not so simple with P-ch (one needs about 3-4 times as many P-ch MOSFETs to chose from to get the same number of close matches, as for N-ch).
Source resistors will improve matching at lower currents but the voltage drop across them is far to low to make a difference at high currents due to the relatively low Gm of the laterals. The models do not show that in the real world they can vary quite a bit. It's gotten better with the newer production parts (J162/K1056), but not drastically so, especially concerning the P-ch part. When laterals were first introduced a number of manufacturers used them in their designs, strating with Hitachi themselves, but there were also Kyocera, Sanyo, and a ton of PA amp manufacturers. In the HiFi realm, it's quite conspicuous that most amps were of fairly low power in order to use a single pair. Amps that used multiple pairs invariably had matched parts (at least as far as i can tell from experience with Hitachi, Kyocera, Sanyo, Strasser, and a numer of other manufacturer's amps).

Thank you for participation here. Your knowledge about latfet is very wellcome and can help to deign better amp here. I know that it's posible to lower didtortion by omitting source resistors if someone can get good matching.

[dadod]

Originally Posted by DUG

Just a few questions/comments

R46/R47 not symmetrical?

No equivalent for R63 on negative side?

FET gate resistors...220R in positive side and 150R in negative side.

Output quiescent current not adjustable?

You got good eye.
R46/R47 are different to set DC offset at output to zero. Actually it will contain two 12 ohm resistors and 100 ohm trimer.
About need for R63(to compensate for bias current fluctuation) I am not sure do I need the same on negative side, I have to simulate more.
MOSFET gate resistors are of different value as N and P MOSFER are with different input capacitance.
R64 is a trimpot actually (2k) used to set the quiescent current.

[dadod]

Originally Posted by Bonsai

Good distortion results and slew rate on your design dadod. I think this clearly demonstrates the role in a CFA that the feedback resistor plays in setting the amplifier gm - you are getting these good results because there is plenty of feedback at HF, but you are able to curtail it at HF with TPC and avoid running into phase shift problems due to the output stage - FET's no doubt allowing this as well.

Yes you've got it right Bonsai, this twist in TPC(connection to the output instead to the VAS collector) improve HF distortion a lot and with BJT's it did not work(for now).

[dadod]

THD20k drops from 14.5 ppm to 2.52 ppm (50W) when C8 C10 moved from Q6 Q8 collectors to the output, this is 21 dB.