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Old 22nd September 2010, 10:57 AM   #1
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Default Reduced power with lateral fets ???

Since i installed lateral mosfets in my mosfet citation 12, i am only getting half the power out on the onset of clipping.

With two IRFP450's i get 120W into 1.95 ohms and 100W into 3.9 ohms.

With lateral mosfets i only get 32 watts into 1.95 ohms and 50 watts into 3.9 ohms for the same supply voltage.

Why is this ? Does laterals need a higher drive voltage for a given output voltage ?
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Old 22nd September 2010, 11:03 AM   #2
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Quote:
Originally Posted by Tekko View Post
Since i installed lateral mosfets in my mosfet citation 12, i am only getting half the power out on the onset of clipping.

With two IRFP450's i get 120W into 1.95 ohms and 100W into 3.9 ohms.

With lateral mosfets i only get 32 watts into 1.95 ohms and 50 watts into 3.9 ohms for the same supply voltage.

Why is this ? Does laterals need a higher drive voltage for a given output voltage ?
There's probably two effects:
- the laterals need higher gate-to-surce voltage which means the drivers hit the rails with the output still apprciably below it;
- the laterals have significant internal resistance meaning that with higher output current (especially in low impedances like your 2 and 4 ohms) you lose significant voltage across the device.

Not sure which effect is dominant here.
You could check the difference in Vgs in the data sheets, that should make it clear.

jan didden
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Old 22nd September 2010, 11:04 AM   #3
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Tekko View Post
Since i installed lateral mosfets in my mosfet citation 12, i am only getting half the power out on the onset of clipping.

With two IRFP450's i get 120W into 1.95 ohms and 100W into 3.9 ohms.

With lateral mosfets i only get 32 watts into 1.95 ohms and 50 watts into 3.9 ohms for the same supply voltage.

Why is this ? Does laterals need a higher drive voltage for a given output voltage ?
Their transconductance is much lower,about 1 to 2S, meaning that you
have to paralel two or better, three, to have limited losses with low loads.
Otherwise, they have lower threshold voltage than the verticals IRFPs.

Last edited by wahab; 22nd September 2010 at 11:06 AM.
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Old 22nd September 2010, 11:06 AM   #4
Mooly is offline Mooly  United Kingdom
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Laterals (a single pair) are not suitable for driving such low impedance loads. The on resistance is far higher than a HEXFET.

Are they "double die" laterals you are using ?
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Old 22nd September 2010, 11:12 AM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Tekko View Post
With two IRFP450's i get 120W into 1.95 ohms and 100W into 3.9 ohms.
is this a quasi complementary that has 1pr of Nchannel devices?

1pair of laterals is probably good for 60W to 90W into 8ohms.
2pair of laterals for 120W to 180W into 8ohms.
4pair of laterals for 240 to 360W into 4ohms.
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Old 22nd September 2010, 11:13 AM   #6
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They are the ACD100NSD model, the same ones used in the NX200 200W into 4 ohms amp from Class D

I do think about adding the second pair, i bought four of them.
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Old 22nd September 2010, 11:20 AM   #7
Mooly is offline Mooly  United Kingdom
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Why did you want to fit Laterals ?

Just looked at the price of those ACD100NSD... outrageous
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Old 22nd September 2010, 11:24 AM   #8
Mooly is offline Mooly  United Kingdom
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I take it this is the amp,
http://cygnus.ipal.org/mirror/www.pa...s/citation.pdf
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Old 22nd September 2010, 11:31 AM   #9
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Yup!

I wanned to try out laterals since they are made for audio, nut my ears cannot detect any difference in sound quality.

Btw i've heard these laterals were cheap compared to other laterals.

Heres a video: YouTube - HK pass modified citation 12 Lateral mosfet
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Old 22nd September 2010, 11:36 AM   #10
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Mooly View Post
Why did you want to fit Laterals ?

Just looked at the price of those ACD100NSD... outrageous
Not that much, although he better had opted for 2SJ162/2SK1058,
even this mean more pairs..

Class D - ACD100NSD Lateral Mosfets
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