Mosfets

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XXL
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Mosfets

Post by XXL » Fri Sep 06, 2019 5:20 pm

Iv been looking around for different mosfets to try out. Every time I check the data sheet they say obsolete. So I don’t really want to design something based on an obsolete item.

Most of the round type SD series say obsolete, SD2931, SD2933, SD2943, etc.

Mostly all MRF series I see are gone.

Bipolar transistors are well gone. BLX series...... what’s left?

Only seems to be rectangle type fets now.

Bton-FM
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Re: Mosfets

Post by Bton-FM » Fri Sep 06, 2019 8:06 pm

The ma/com mosfets are still in production (mrf171a , mrf173 ect.)

Krakatoa
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Re: Mosfets

Post by Krakatoa » Sun Sep 08, 2019 10:19 pm

Many of the old bipolar types of RF power transistors are made now by a company called ASI or Advanced Semiconductor Inc. The BLX15 for example, is in their catalog, so you can still maintain or build equipment wtih some of the device types that were obsoleted by their original manufacturer some time ago.

But if you want to try out some brand new shiny mos-fets, recently there has been released the MRF101AN that can push 100W in a convenient TO220 package. There is a demo board for 88-108 MHz published with all the details in the manufacturer's website.... just in case...

nrgkits.nz
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Re: Mosfets

Post by nrgkits.nz » Mon Sep 09, 2019 12:44 am

Have a look at NXP Semiconductor, they have a range of modern dual LDMOS devices.

https://www.nxp.com/products/rf/rf-powe ... F-INDUST-1#/

The ones I use are the MRFE6VP5300N (300W) and MRFE6VP5150N (150W), both only require 1W of drive, 1.5W max.

You can get a higher output impedance with a dual LDMOS package as opposed to a single ended devices, and therefore a much better broadband match.

Albert H
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Re: Mosfets

Post by Albert H » Mon Sep 09, 2019 11:11 pm

I got three MRF101AN TO220 FETs this morning. I built my first PA this afternoon. 60V supply, 800mW input, 100W anywhere you want from 87.5 - 108 MHz. These are available from Farnell or Mouser for around £18 - pretty cheap for a really useful device!
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thewisepranker
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Re: Mosfets

Post by thewisepranker » Mon Sep 09, 2019 11:20 pm

Did you use the reference design from fig. 32/33 in the datasheet?
This one: https://www.nxp.com/docs/en/data-sheet/MRF101AN.pdf

Albert H
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Re: Mosfets

Post by Albert H » Mon Sep 09, 2019 11:25 pm

It's very similar, but laid out to fit a heatsink box I have in stock. These are really good - cheap, easy to mount, efficient and pretty robust.
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Re: Mosfets

Post by thewisepranker » Tue Sep 10, 2019 12:00 am

Hopefully you built a better filter. 2f is only -32 dBc for that design or in the old money that your test equipment accepts, about 1.78 V RMS.

Albert H
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Re: Mosfets

Post by Albert H » Tue Sep 10, 2019 12:28 am

On 98.4 MHz before the filter, the second was -44dBc and the third was -49 dBc. When the filter was added, the second was -71dBc and the third was in the grass. The filter is separated from the PA by a tinplate screen, and the coils in the filter are aligned to minimise mutual coupling. The capacitors in the filter are "AVX" branded chip caps.

The gain of these amplifiers is proportional to the supply voltage, which could prove useful if you need a very specific power output.
"Why is my rig humming?"
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