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Old 1st December 2006, 04:31 PM   #731
Tyimo is offline Tyimo  Hungary
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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
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Old 1st December 2006, 05:43 PM   #732
Ryssen is offline Ryssen  Sweden
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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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Old 1st December 2006, 05:51 PM   #733
lineup is offline lineup  Sweden
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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 0.95C/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 0.5C/W.


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

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

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


Isn't SEWAPLUS a good name!


lineup
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Old 1st December 2006, 06:19 PM   #734
Tyimo is offline Tyimo  Hungary
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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
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File Type: zip sewa-se-2.zip (64.1 KB, 205 views)
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Old 1st December 2006, 07:31 PM   #735
lineup is offline lineup  Sweden
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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
https://ec.irf.com/v6/en/US/adirect/...ctID=IRFP264N:
https://ec.irf.com/v6/en/US/adirect/...ctID=IRFP260N:
https://ec.irf.com/v6/en/US/adirect/...ctID=IRFP254N:

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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Old 1st December 2006, 07:49 PM   #736
lineup is offline lineup  Sweden
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Smile 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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Old 2nd December 2006, 05:50 AM   #737
Tyimo is offline Tyimo  Hungary
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Quote:
But I will post my schematic suggestion later today or tomorrow.
Thanks Lineup brother!

Heavy greetings:

Tyimo
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Old 2nd December 2006, 11:20 AM   #738
Mad_K is offline Mad_K  Norway
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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.
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Old 2nd December 2006, 11:28 AM   #739
Mad_K is offline Mad_K  Norway
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IRFP250N is a good choice for trying to maximize the SEWA design
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Old 2nd December 2006, 11:56 AM   #740
Tyimo is offline Tyimo  Hungary
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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.
Thanks Mads!

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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