Jacco, Would it be a better idea to sink the diode seperately vs with the fets in order to keep it from the effects of the heat generated by them, or do you want a degree of thermal tracking. With the thermistor you have this already, so it seems that seperation may be a good thing. Sorry to myself for OT comment.
So how much heatsinking does each diode need? Could you just turn them up and mount them to an aluminum bar running between them? What size bar?
Would a bar like this work: 50mm wide x 6mm thick and say 300mm long for 4 each MUR3020?
Rush
Probably should move this discussion, but if you look at the graphs on the datasheet, you see how the vdrop changes with both current and temperature. Assuming that temperature is held constant, if you drop maximum current rating of fet of 18A, then you probably dissipating 17w max. The diode starts to conduct at around .5V, but as the current increases, the vdrop increases. It maxes out at aobut 1V. Your max dissiapation will be VxI of course. You haev to consider the case to heatsink transfer and how they have that rated. It will hae to be a solid heatsink to maintain temps at or near that 25C mark. Any sort of finning adds so much, i think it would be best to find a low profile version of somethin that long, even if it only had 1" fins or less.
I did 17 years at MUR-Land!, Not doing MUR's but, I'm just say'in. Yes, they do, do some things right!. Their Schtky(spelling) technology has been 2nd to non since inception.
I like my diodes at 25.45mm spacing, or so, away from anything! They have all the high current Voo-Doo of any other component!
But then... Why do "we" use a 3020? 200Volts? Why? What do we need 200V for??? 30A, O.K. well, I think there is really a time, current, power thing goin on that we can't capture (without blind experience) due to the 120 cycle re-charge, and audio nature, Bla, Bla.
My point is, I have'nt had one blow up, and I use 2535. 12.5 amps per leg and In ||(always) 25A with a .325 MaxVfwd!!!! 1/2 the power and 1/2 the FwdV of the 3020! 1/2 the loss of the 3020! With only 5 less Cont. A transeint power???
I just don't feel comfy with these "ultra fast", "soft-recovery" bla, bla,,, 1-2V diodes! I've seen good results from the low phi schotky(sp) stuff if you go big enough for current surge requirements.
Comments????
I like my diodes at 25.45mm spacing, or so, away from anything! They have all the high current Voo-Doo of any other component!
But then... Why do "we" use a 3020? 200Volts? Why? What do we need 200V for??? 30A, O.K. well, I think there is really a time, current, power thing goin on that we can't capture (without blind experience) due to the 120 cycle re-charge, and audio nature, Bla, Bla.
My point is, I have'nt had one blow up, and I use 2535. 12.5 amps per leg and In ||(always) 25A with a .325 MaxVfwd!!!! 1/2 the power and 1/2 the FwdV of the 3020! 1/2 the loss of the 3020! With only 5 less Cont. A transeint power???
I just don't feel comfy with these "ultra fast", "soft-recovery" bla, bla,,, 1-2V diodes! I've seen good results from the low phi schotky(sp) stuff if you go big enough for current surge requirements.
Comments????
Sorry to Hijack the thread.
I'm in the middle of planning the heatsink layout to test some V2 boards and this is new information to me that the diodes should not be mounted on the same heatsink as the MOSFETs.
I keep changing direction and going nowhere.
Rush
Changing direction? Going nowhere?
You must be going in circles....
This is Engineering bud! Account for every component and it's performance level neccessary for the sound to be the number 1 criteria!
Trouble is, you can't learn how to do this somewhere. Even if we try to prioritize the theory, etc., etc..? We just don't seem to be able to work down to the Nitty-Gritty concencus...
It's all a buch of carefully selected compromises
You must be going in circles....
This is Engineering bud! Account for every component and it's performance level neccessary for the sound to be the number 1 criteria!
Trouble is, you can't learn how to do this somewhere. Even if we try to prioritize the theory, etc., etc..? We just don't seem to be able to work down to the Nitty-Gritty concencus...
It's all a buch of carefully selected compromises
I did 17 years at MUR-Land!, Not doing MUR's but, I'm just say'in. Yes, they do, do some things right!. Their Schtky(spelling) technology has been 2nd to non since inception.
I like my diodes at 25.45mm spacing, or so, away from anything! They have all the high current Voo-Doo of any other component!
But then... Why do "we" use a 3020? 200Volts? Why? What do we need 200V for??? 30A, O.K. well, I think there is really a time, current, power thing goin on that we can't capture (without blind experience) due to the 120 cycle re-charge, and audio nature, Bla, Bla.
My point is, I have'nt had one blow up, and I use 2535. 12.5 amps per leg and In ||(always) 25A with a .325 MaxVfwd!!!! 1/2 the power and 1/2 the FwdV of the 3020! 1/2 the loss of the 3020! With only 5 less Cont. A transeint power???
I just don't feel comfy with these "ultra fast", "soft-recovery" bla, bla,,, 1-2V diodes! I've seen good results from the low phi schotky(sp) stuff if you go big enough for current surge requirements.
Comments????
Sounds like your in more of a position to comment then anybody. Perhaps Nelson was thinking about the heat possibilities when he picked them, assuming theywould be put with the fets. The data shhet shows they can take quite a bit of heat, just affects their response.
The big deal with PSU diodes is what happens down around 1W(Funny thing that 1st watt). Well, maybe something like that. When the diode goes from Fwd/Rvs current it has a little trouble decideing and creates a jittery looking noise before it eventually decides what's going on with all them electons and barrier voltages. It's tough to see with the scope but a diode in series will help!
So, a "normal" diode has Capacitance and, we'll call it noise at 0V crossing... So that's another problem. It's also stuck dealing with it's C while the signal (AC Line) is doing some'in else Oh sh*%t!
So, we have "FAST", "Ultra FAST" "Soft" and baby's but,etc... and we have shotcky's(sp)??? Personally, I'ld use a 6C3 rectumfrier! Solves all dem problems...
Anyway, I really like the low loss of shctky(sp) and the C of a Schtky is not the same as Switching loss C or Drain C or whatever! They really do compete with the so called low noise Rectumfriers and they can handle High current surges with reasonable expectations. Just my 2 Cents
So, a "normal" diode has Capacitance and, we'll call it noise at 0V crossing... So that's another problem. It's also stuck dealing with it's C while the signal (AC Line) is doing some'in else
Oh sh*%t!So, we have "FAST", "Ultra FAST" "Soft" and baby's but,etc... and we have shotcky's(sp)??? Personally, I'ld use a 6C3 rectumfrier! Solves all dem problems...
Anyway, I really like the low loss of shctky(sp) and the C of a Schtky is not the same as Switching loss C or Drain C or whatever! They really do compete with the so called low noise Rectumfriers and they can handle High current surges with reasonable expectations. Just my 2 Cents
I got simple tought about diodes
Yest they change with temperature
so the first loud passage will have one response and a second time wise close will have different response as diode is warm from before
Wuld not be beter to try and keep them at aconstantsortofthemperature Kind of thing?
EG same heat sink as mosfets as that is prety and big themperature won't change to quiqk.
And realisticaly speaking how often are those diodes asked to came in to play?
Yest they change with temperature
so the first loud passage will have one response and a second time wise close will have different response as diode is warm from before
Wuld not be beter to try and keep them at aconstantsortofthemperature Kind of thing?
EG same heat sink as mosfets as that is prety and big themperature won't change to quiqk.
And realisticaly speaking how often are those diodes asked to came in to play?
I suppose I also might say, Nelson wants all of us to experience reliability in his Pass products, his First Watt products and in his DIY presentations etc. We really don't want to be bangging our head and learning about those kind of difficulties, the "hard" way. In other words, I believe he is relatively conservative 1/2 the time. (Notice I only give him credit for 1/2 the time). Now and then he's thinking brave and tell's us something our grandparents or parents would not have said. But it's for the benifit of the Audio Entertainment, the coup de'gra, or as he would say "the raison detre". the reason we do this!
Having said that
I should shut up!!!
Nelson has a good sense about all this mostly cause he's been playun with it for 30-40 years>
the best bthing,,, he'll (or someone else) probably speak up if I try to stear you wrong
Having said that
I should shut up!!!Nelson has a good sense about all this mostly cause he's been playun with it for 30-40 years>
the best bthing,,, he'll (or someone else) probably speak up if I try to stear you wrong
Nothing wrong with that.
Papa takes the safe approach, adjusting the bias setting with the amp as hot as it will ever get.
In effect, conditions will at all times be such that the diodes will never stampede.
Couple of downsides, one is that temperature across a large heatsink varies considerably.
Yes, I guess so Buzzforb? The schotky(sp) process produccess a fwd diode drop about .3, + or - .1 or 2 vs. the soft/fast stuff being 1-2V or more fwd Vbe! More H.S. More loss from the expected Xfmr out, more Pd. on the Diodes, etc. etc..
Where I work daily, we do an artificial diode with a big FET. Syncronous Rectifier! We just turn it on and off when it is supposed to happen. Just Gotta try to work one out for our purposes someday... with soft switching!
Where I work daily, we do an artificial diode with a big FET. Syncronous Rectifier! We just turn it on and off when it is supposed to happen. Just Gotta try to work one out for our purposes someday... with soft switching!
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