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Old 14th March 2010, 11:14 AM   #1
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Default 150W MOSFET Amplifier with IRFP250x2

This circuit is upgrade on BUZAMP from Elektor. Use only N-mosfets, with +/-50V DC give 150W on 4R load.
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Old 14th March 2010, 11:22 AM   #2
latala is offline latala  United Kingdom
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I am interested in your amplifier can you please give furthere details
regards Trev
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Old 14th March 2010, 11:33 AM   #3
wahab is offline wahab  Algeria
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BC550C have a too low VCE of 45V for the +-50V rails..
Use BC546B, they have a 65V VCE..
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Old 14th March 2010, 11:45 AM   #4
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Thanks Wahab. I not made this amplifier since 1995. 2SC2240, 2N5551... also can be used.
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Old 14th March 2010, 01:14 PM   #5
russel is offline russel  Europe
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Quote:
Originally Posted by apexaudio View Post
This circuit is upgrade on BUZAMP from Elektor. Use only N-mosfets, with +/-50V DC give 150W on 4R load.

I think you may hit thermal stability problems. Use a compound mosfet and mount the drivers in thermal contact with the Vbe multiplier that sets the bias current.
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Old 14th March 2010, 01:21 PM   #6
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BD139 is on heatsink with output fets for termal compenzation.
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Old 14th March 2010, 02:29 PM   #7
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This two old modules (about 20 years) same circuit without curent limit, with BF422/BF433 and BUZ21x4 stil in use work on +/- 36 DC.
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Old 14th March 2010, 02:35 PM   #8
russel is offline russel  Europe
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Quote:
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BD139 is on heatsink with output fets for termal compenzation.

What bias current do you use?
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Old 14th March 2010, 02:37 PM   #9
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What bias current do you use?
50mA
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Old 14th March 2010, 03:00 PM   #10
russel is offline russel  Europe
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OK, thats quite low for a FET. Lateral FETS usually need 150mA and Vertical FETS are run at 400mA. If you look at the transfer characteristics in fig 3 on the link: http://www.datasheetcatalog.org/data...rf/irfp250.pdf

You can see if you ran it at 400mA there is chance of thermal runaway.
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