The AM Forum

Well, it looks like the FQA11N90C series of FET's has bit the dust and will be discontinued.
There are a few suppliers that have a small amount of stock but after they are gone, that's it.
So what is a guy to do if he wants to build one of Steve's (WA1QIX) high power RF deck?
I'm sure someone may know of an appropriate substitute.
Thanks,
Don

The C3 series from Cree (Wolfspeed)

They've been around for ages and are far easier to drive.

JB.

Don,

Where have you found the Product Change Notice? I can't find it.

John

Mouser has an End of Life notification but they are also getting another 900 in later in April, so theoretically, they are being phased out but like a lot of stuff, they will be there in NOS for years.

As was mentioned, there are many possible alternatives, but for 80 and 160 meters Class E, they are still very tough and reliable and Steve touts the large chip structure and the high rate of heat transfer to the sink.

Besides the Class E circuits, they are featured in Class B modulator drivers by a Frank Carcia as well as Steve.
There is no reason to choose a “new” device unless it performs better in s particular application better than an older reliable device like this.

Yes, the new GFZ balanced Mosfet driver uses 8 of them. I just sent off for the boards.

As with most SS designs, it may be a good idea to buy 10 or so to have a few spares, just in case. Frank says that there are easy R changes to use other devices in the event that the venerable 11N90 is no longer available.

John

I believe that some of the factors that need consideration include
Die size
Heat transfer from chip and case
The Safe Operating Area

Operation outside the SOA can result in a runaway self destruction of a device and Drain voltage and current will be limited in a lot of devices that might look good initially

The FQA11C90 has a large die, very good heat transfer and the SOA is large SOA space so that it can be used at over 1 amp per device continuous current at over 100 volts. In applications needing more stable current output, the devices can be put in parallel to allow more current at a given voltage.

Steve has stuck with this device for more than a decade for good reason and Frank is a very good designer and also recognizes these factors.
It is always wise to listen to experienced designers and builders so we can understand all the factors in choosing devices that are appropriate to our applications.

the mouser EOL announcement is almost 2 years old.

http://amfone.net/Amforum/index.php?topic=46125.0

Haven't found a suitable replacement yet, but also have just started looking.

The most important design criteria for the class E rigs has always been reliability.  A standard MOSFET is a VERY rugged and reliable device, which is why I choose these types of devices.  The FQA11N90 was (is) definitely the best price/performance device for the particular application (high power class E rf amplifiers) out there at this time.

In real world use, transmitters are reasonably regularly subjected to being operated (often at full power) into:  No load, short circuit load, horribly mistuned, antenna failures during operation, short circuits at the end of a long piece of coax (this is a particularly bad situation) during operation, antenna tuner arc-overs, under-driven, over-driven, etc. etc. etc.   

The MOSFETs have to be robust enough to survive these transient situations, and the overload system must be able to shut things down before any damage occurs.

As of 7-7-23
Mouser DISCONTINUED  0 STOCK.
Digi key DISCONTINUED  0 STOCK.

There appears to be places that have NOS parts for premium prices but when they are gone, what will we use to replace them?

Seems like Richardson has 19000 in stock.
The surplus market may serve for a while. There are a ton of FETs, but they lack some important attributes of the FQA11c90.
The SOA curve is a key factor in identifying the kind of thermal stability needed.
The FQA6N90 seems interesting, but the on resistance is over 2 ohms and current is a bit less, though it has a good SOA characteristic and seems fast enough and dissipates power well in the TO3pn package. It is obsolete too, however….

Looks like the FQA13N80-F109 is still available and not on the endangered species list.
Just about the same specs but 800 volts.