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25th November 2009, 10:35 PM
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#1 |
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diyAudio Moderator Emeritus
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Mosfet Gyrator using the IRF840
Could I use the IRF820 instead? With the same values?
I'm thinking of building a Gyrator for my Baby Huey EL84. Maybe even two. And I have IRF820's in my parts bin. I know very little about solid state things like mosfets, hence my question. R1, R2 330k Ohm C1 4.7uF D1 ZD15 R3 33 Ohm Q1 IRF840 Also any tips for improving this gyrator? 
Last edited by Bas Horneman; 25th November 2009 at 10:43 PM. |
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25th November 2009, 11:30 PM
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#2 |
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Did it Himself
diyAudio Member
Join Date: Nov 2003
Location: Gloucestershire, England, UK
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The 820 will do less current than the 840. Look on the datasheet to see if it sufficient for your needs.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more |
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26th November 2009, 10:38 AM
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#3 |
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diyAudio Moderator Emeritus
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Thanks Richard,
I'm looking at 80mA per gyrator. The 820 can handle 2,5A the 840 something like 8A. That is the spec Id. But I'm not sure how to transfer that current rating into the rating of the mosfet as it has been used in the circuit. I'll just build it and see... Last edited by Bas Horneman; 26th November 2009 at 10:56 AM. |
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26th November 2009, 10:44 AM
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#4 |
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diyAudio Moderator Emeritus
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Another one. Where it appears the zener is the other way around?
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26th November 2009, 10:44 AM
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#5 |
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Did it Himself
diyAudio Member
Join Date: Nov 2003
Location: Gloucestershire, England, UK
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I think at that current it should be fine. What voltage will be across it? You also need to consider the power dissipation and that you are within the device safe operating area (SOA curve) again both are on the datasheet - former in the table, latter as a graph.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more |
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26th November 2009, 10:50 AM
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#6 | |
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diyAudio Moderator Emeritus
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Quote:
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26th November 2009, 12:06 PM
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#8 | |
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diyAudio Moderator Emeritus
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Quote:
Cheers, Bas |
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26th November 2009, 12:08 PM
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#9 |
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diyAudio Member
Join Date: Sep 2004
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Like the second image here:
http://www.diyaudio.com/forums/blogs...-follower.html Only you want to take your output from the anode (gyrator) rather than that images source (follower). Cheers! |
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26th November 2009, 02:00 PM
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#10 |
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diyAudio Member
Join Date: May 2007
Location: Eskilstuna, Sweden
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Bas,
This is not a strict gyrator. Despite that, it has two advantages. You can adjust output voltage(vary R3) and it has a lot less ripple than a typical MOSFET gyrator. Still it has the exactly the same high Zout. C3 is not part of the gyrator.You might also change R1, C1 to your values if this suits you better. 
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Brgds Lars Last edited by revintage; 26th November 2009 at 02:05 PM. |
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