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Any help?  First attempt at a "hybrid" using depletion MOSFETS
Any help?  First attempt at a "hybrid" using depletion MOSFETS
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Old 1st August 2020, 06:39 AM   #71
kodabmx is offline kodabmx  Canada
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Any help?  First attempt at a "hybrid" using depletion MOSFETS
Bingo! Thanks for that
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Old 1st August 2020, 02:48 PM   #72
mbrennwa is offline mbrennwa  Switzerland
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Any help?  First attempt at a "hybrid" using depletion MOSFETS
Quote:
Originally Posted by kodabmx View Post
Out of curiosity, What would be an appropriate inductance if I was to try and choke load it instead?



1mH? Am I close?



Thanks everyone!
I was in the same boat until I realised that a constant current source made from a transistor or two is often a better choice than an inductor (smaller, cheaper, more linear). Nelson Pass has a few CCS suggestions in his papers.

Oh, 1 mH seems like way too low, but I didn't do the math.
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Old 1st August 2020, 06:41 PM   #73
kodabmx is offline kodabmx  Canada
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Any help?  First attempt at a "hybrid" using depletion MOSFETS
Ya I'm starting to think a CCS would be easier. I could even use a second pair of the same MOSFETs... 1mH might work for the PS filter though instead of 1R.
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Old 1st August 2020, 08:27 PM   #74
tikiroo is offline tikiroo  New Zealand
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If the inductance was below the source (see the MoFo thread) you need upwards of 30 mH depending on how low you want to go in frequency. With the inductance above the drain, the impedance is much higher, extremely high in your case as you have no local feedback, and it only becomes practical if you can use a centre-tapped choke (e.g. the primary of a 115+115 power transformer) in balanced mode, where you can get tens or hundreds of Henries.

A CCS works well but you don't get the extra voltage swing and efficiency is still half of an inductor loaded output. That then evolves to a modulated CCS where the sum of the current in the top and bottom halves is kept constant. It is then effectively operating push-pull but without the second harmonic cancellation as the input signal only drives one half. The ALPHA Nirvana on this forum is one example.
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Old 3rd August 2020, 10:12 PM   #75
kodabmx is offline kodabmx  Canada
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Any help?  First attempt at a "hybrid" using depletion MOSFETS
Ya?

Today I got finally 120V 300W bulbs. I had to drive over 100 km round trip to get them - Seems Sylvania doesn't sell them in Canada anymore.

The amp is improved with them though.

Next my idea will be to swap the MOSFET and the bulb to make it a source follower. I think that will lower the Zout and the input capacitance, yes?
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Old 4th August 2020, 03:10 AM   #76
TonyTecson is offline TonyTecson  Philippines
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incandescent lamps are going the way of the dodo bird, same with compact flourescents..
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