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Balanced Monoblock F4s with very high Bias
Balanced Monoblock F4s with very high Bias
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Old 5th December 2018, 01:01 PM   #21
Zen Mod is offline Zen Mod  Serbia
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Balanced Monoblock F4s with very high Bias
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Yes, the uber important aspect of diy for me is the fun part.
yup

at least for last decade , for me it's 90% , or even more

learning is fun
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Old 5th December 2018, 02:59 PM   #22
mpmarino is offline mpmarino  United States
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Quote:
Originally Posted by Zen Mod View Post
good luck finding a mate for IRFP150
Maybe look into IRFP140 / 9140? Still single die (I think) but you trade some voltage capacity for some current capacity. Not much more capacitance than 240 / 9240 too.
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Old 5th December 2018, 03:40 PM   #23
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Balanced Monoblock F4s with very high Bias
I was interested not just in current but also in xconductance
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Old 5th December 2018, 05:10 PM   #24
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Balanced Monoblock F4s with very high Bias
Quote:
Originally Posted by Zen Mod View Post
1. ok
2.5U/500 Modushop , as minimum
3.no worries ; Iq is not changing drive demands

Zen Mod, I was thinking about the chassis, 500mm deep will be a bit on the bigger side, difficult to position it in the room. I ran numbers with 400mm deep (see attached table), it looks like OK;

i) With an efficiency/de-rating of 80% and

ii) Target heat sink temperature of max 55C in a 30C room


Per chassis they can dissipate 286Watts, which is very close to 288Watts dissipation need from 24V rails and 1A bias per device.


What do you think?
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Old 5th December 2018, 05:22 PM   #25
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Balanced Monoblock F4s with very high Bias
5U/400 is already darn big

from my experience with 4U/400 and I just once made an amp with 5U/400 ...... I believe 140W per side is too optimistic

however , I can't be sure 100% , just because I didn't make any notes

so , when you finish it , let us know
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Old 5th December 2018, 05:49 PM   #26
syracuze is offline syracuze  United Kingdom
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Balanced Monoblock F4s with very high Bias
Quote:
Originally Posted by Zen Mod View Post
5U/400 is already darn big

from my experience with 4U/400 and I just once made an amp with 5U/400 ...... I believe 140W per side is too optimistic

however , I can't be sure 100% , just because I didn't make any notes

so , when you finish it , let us know

Cool, thanks! For sure, will do!


Though, I am still in the process of idea stage, thinking what else overkill that I can do

Obviously, power supply is the usual suspect! My F5 has 8 x 47000 uF capacitors, if I don't exceed that with a good margin, that is a failure on my side!
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Old 6th December 2018, 03:48 AM   #27
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Quote:
Originally Posted by Zen Mod View Post
I was interested not just in current but also in xconductance

Please explain. looks like the 140 Gfs at 11 is somewhere in between the 6.9 of the 240 and 13 of the 150.

Are you worried about the 'curve'? i only ask because I don't know what I'm talking about
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Old 6th December 2018, 04:07 AM   #28
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Balanced Monoblock F4s with very high Bias
sorry , my bad .... need to re-check IRFP9140 datasheet , for oomphteentht time

was distracted ,while typing/thinking ,with zillion wires of some turtle , so had just half of usual half brain

now just semi awake .....
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Old 6th December 2018, 05:32 AM   #29
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well then, I forgot about the 9140 .... 6.2

BTW - I really don't know what I'm talking about.. just that I've been using the '140s for forever and beating the crap out of them
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Old 6th December 2018, 07:40 AM   #30
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Quote:
Originally Posted by mpmarino View Post
Please explain. looks like the 140 Gfs at 11 is somewhere in between the 6.9 of the 240 and 13 of the 150...
Transconductance of IRF mosfets (square law device) is proportional to square root of drain current.
I usually estimate transconductance at intended bias by :
Code:
gfs(Id1) ~ gfs(Id2) * sqrt(Id1/Id2)

where :
gfs(Id1)  transconductance at intended drain current
Id1       intended drain current
gfs(Id2)  datasheet transconductance at cited drain current
Id2       datasheet cited drain current
Estimating from Vishay datasheets :
Code:
             Datasheet           Estimate
           gfs   @Id(A)   gfs @1.3A   gfs @2A
N-ch
IRFP140    9.8    19        2.56       3.18
IRFP150   13      25        2.96       3.67
IRFP240    6.9    12        2.27       2.82
IRFP244    6.7     9        2.54       3.15
P-ch
IRFP9140   6.2    13        1.96       2.43
IRFP9240   4.2     7.2      1.78       2.21
Please note that the estimate is based on Vishay minimum gfs value, no description of typical value. Spread of value is pretty wide, a maximum gfs device can have double the transconductance of a minimum gfs device.
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