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Freescale MRF Transistor - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


Corvus
Post subject: Freescale MRF transistor Posted: Fri Oct 05, 2007 9:19 am

Captain


Joined: Mon Jul 18, 2005 12:55 pm
Posts: 8
Geetings!

I am experiencing the sudden death of lots of PA pallets mounted with MRF377 transistors. Anyone else with the same problem? I am just wondering if its my own problem or in fact is an inherent problem with this kind of transistor. People said is better to change to NXP. Why? Any solution finded with MRF?

Cheers!


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IR
Post subject: Posted: Fri Oct 05, 2007 3:04 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Greetings Corvus!

You are not the only one!

A while ago I was working on a PA design which was made of MRF374, and MRF377. I had the same problem with this series of transistors. Although, as far as I recall, the problem was with the MRF374.

In my case the problem was that MRF374 was used to drive another MRF374 and the amount of input power to the second MRF374 was too high. This series of transistors doesn't have a device with an intermediate output power level in the range of 60-80W in contrast to the UMTS line where the variety of devices is much larger: MRF21010, MRF21030, MRF21045, MRF21060, MRF21090....

The problem in essence has to do with a protection diode that is located between the Gate and Source. This diode is meant to protect against reverse voltages. The malfunction happens during a high voltage RF swing, which causes the diode to clamp the negative part of the cycle, as a result, a short-circuit is caused between the Gate and Source. I had to change a lot of transistors until I switched to another manufacturer.


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Corvus
Post subject: Posted: Mon Oct 08, 2007 5:56 am

Captain


Joined: Mon Jul 18, 2005 12:55 pm
Posts: 8
Hi IR!

I appreciate your help!I want to change the manufacturer of my transitors but I can not find another PA pallet implemented with other transistor.Do you know any manufacturer that implements pallets of powers of 50Wrms or 100Wrms but without Freescale transitors?


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IR
Post subject: Posted: Mon Oct 08, 2007 6:16 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
I think that NXP do that.

I will also check other manufacturers for you. Unforutnately, I am already long time out of the PA arena.


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Corvus
Post subject: Posted: Mon Oct 08, 2007 11:30 am

Captain


Joined: Mon Jul 18, 2005 12:55 pm
Posts: 8
Hi again,

Anybody knows how to avoid or short circuit the diode protection in the MRF transistor? Is it possible?

thanks


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IR
Post subject: Posted: Mon Oct 08, 2007 1:51 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
As far as I know, the only way is to provide the required input power so that the diode will not go into operation. Once the diode is clamped it is too late.

Look in the device data sheet what is the allowed input power level and don't go over it.

I hope this helps.







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