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 1st December 2006, 05:31 PM #731 diyAudio Member   Join Date: Nov 2002 Location: Hungary Thanks Lineup! I understand your suggestion, but I cann't believe that 2.5A would be too much for 1 IRFP150N in the CCS. I donn't know how to connect the output caps in your double CCS version. Could you help me with a drawing? I would like to use your way, if it is not so complicated. Tyimo
diyAudio Member

Join Date: Dec 2003
Location: Sweden--> Here
Quote:
 I understand your suggestion, but I cann't believe that 2.5A would be too much for 1 IRFP150N in the CCS.
I tried the Sewa with 2,7A,and my heatsinks got hot!!Well,I guess it depends on how big you heatsinks are.
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Regards Åke

diyAudio Member

Join Date: Dec 2005
Location: the north
okay
I will do some math!
Remember, this is what 50% of making a good power amplifier is about.
-------------------------------

Thermal resistances coefficients
I do not know what is the approximate ~ rating of your heatsink.
But I will use 0.5 C/W here.
Insulator bricks, I will use 0.4 C/W ( I asked Nelson one time. He agreed, 0.5 C/W is a fair value to use, to be safe )
IRFP150N, 0.95 C/W (this is thermal resistance form outside, case, to inside, junction)

Formula:
Tj = P x ( Rjc + Rcs + Rsa ) + Ta

Temperatures
Ta = ambient temp, air around heatsink, >= room temp
Ts = temp of heatsink, especially area where transistor are
Tc = temp of case, the outside surface of transistor
Tj = junction temp, the important value
Thermal resistance coefficients.
Rsa = heatsink, sink-ambient, gives temp difference heatsink-air
Rcs = insulator brick, case-sink
Rjc = transistor, junction-case, found in transistor datasheet
Quote:
 IRFP150N - Thermal Resistance Rjc Junction-to-Case ––– 0.95°C/W
=======================================

For SEWAPLUS

I use following data.
Ta = 30 C, air temperature around heatsink
Rjc = 0.95 C/W, IRFP150N
Rcs = 0.4 C/W, insulator brick
Rsa = 0.5 C/W, heatsink
Voltage supply 45VDC, at current 2.5A.
Two upper IRFP150 and one as CCS. Gives total 3 x IRFP150 at same heatsink 0.5°C/W.

Resulting junction temperature I get is:
The two upper IRFP150 (27.5 watt per device) will have Tj = 122°C
The CCS one transistor will have Tj = 159°C
Absolute MAX Rating IRFP150N: Tj, junction temperature= 175°C

Remember I said we should avoid to run any transistor above 100°C.
If possible we should try to get it to max 80°C.
In this case 122°C may be acceptable, as we deal with devices with max 175°C.
Many cases, like TO220 case have 150°C max. TO3, Metal Case! have highest max: 200°C

But 159°C is definitely too much!
For one max 175°C transistor.

Isn't SEWAPLUS a good name!

lineup
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lineup

diyAudio Member

Join Date: Nov 2002
Location: Hungary
O.K. Lineup!

Thanks for the math!
I would like to build it as you suggest, but I donn't know how to draw the schematic with 2 CCS Fet, because I donn't know where to connect the output caps!!!

Is it good as in the attached schematic??

Tyimo
Attached Files
 sewa-se-2.zip (64.1 KB, 214 views)

diyAudio Member

Join Date: Dec 2005
Location: the north
Quote:
 Originally posted by Tyimo O.K. Lineup! Thanks for the math! I would like to build it as you suggest, but I donn't know how to draw the schematic with 2 CCS Fet, because I donn't know where to connect the output caps!!! .
Tyimo.

I will draw my own SEWAPLUS suggestion,
with an IRF9610 input transistor for good driving of High Power HEXFET.
I have had some other things to do.
But I will post my schematic suggestion later today or tomorrow.
I will try make a good suitable design for IRFP254N devices.
See more below.

===========================================

IRFP150 is not the perfect device for high power audio.
Rjc (Rth) 0.95 C/W is no good.
For higher power output stages - especially Class A, we should go for 0.70 or lower!

So, I did some research.
https://ec.irf.com/ **** IRF, International Rectifier, recommends the following
3 IRF HEXFET TO247AC for Audio.

IRFP264N 380W Rjc=0.39 C/W RDS(on)=0.060 Ohm
IRFP260N 300W Rjc=0.50 C/W RDS(on)=0.040 Ohm
IRFP254N 220W Rjc=0.68 C/W RDS(on)=0.125 Ohm

I should absolutely try to find IRFP254N.
If possible.
Because it has got a little bit higher RDS(on) (0.125 Ohm) than the other two.
This, 0.125 Ohm, is still a low value. I think Lateral MOSFET (like 2SK1058, 2SK1530) can have like 0.5-1.0 Ohm.
And for audio we should not go too low.
And IRFP254N has got a good low thermal resistance, Rjc=0.68 C/W

Much Regards
lineup
Lineup Audio
http://lineup.awardspace.com/
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lineup

diyAudio Member

Join Date: Dec 2005
Location: the north
IRFP254 IRFP254N spice model multisim

.

here is spice model for IRFP254

i hope I get it working in my EWB Multisim
but i can not fully understand how to do
to add new components to my transistor simulation library
they can sometimes not work, only brings errors

this is a more simple spice model
but it is better than no model at all

Quote:
 .model IRFP254 NMOS(Level=3 Gamma=0 Delta=0 Eta=0 Theta=0 Kappa=0 Vmax=0 Xj=0 + Tox=100n Uo=600 Phi=.6 Rs=9.468m Kp=21.01u W=1.4 L=2u Vto=3.482 + Rd=89.78m Rds=1.111MEG Cbd=3.8n Pb=.8 Mj=.5 Fc=.5 Cgso=1.727n + Cgdo=267.7p Rg=2.601 Is=25.81p N=1 Tt=395n) * Int'l Rectifier pid=IRFC254 case=TO3P * 88-08-26 bam creation
lineup
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lineup

diyAudio Member

Join Date: Nov 2002
Location: Hungary
Quote:
 But I will post my schematic suggestion later today or tomorrow.
Thanks Lineup brother!

Heavy greetings:

Tyimo

diyAudio Member

Join Date: Sep 2002
Location: Norway
Quote:
 Originally posted by Tyimo Is it good as in the attached schematic?? Tyimo

You have to connect D of CCS mosfets together and Source res, of signal mosfets together. This is also where you couple the output.
__________________

 2nd December 2006, 12:28 PM #739 diyAudio Member     Join Date: Sep 2002 Location: Norway IRFP250N is a good choice for trying to maximize the SEWA design __________________ Mads K
diyAudio Member

Join Date: Nov 2002
Location: Hungary
Quote:
 You have to connect D of CCS mosfets together and Source res, of signal mosfets together. This is also where you couple the output.

If the IRFP254N has so good thermal characteristic than I think we could use only one device for CCSI, it isn't it?

Tyimo

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