Hi Gerhard,

73, Stefan

Am 13.01.2011 20:56, schrieb Gerhard Hickl:

Hello Mal and group!

....."a few in parallel"....

My PA is using a single IRFP260N and if I want to put another one "in
parallel" is it necessary to "decouple" the gates by two resistors (a
few Ohms each) or can the gates be paralleled directly?

I would prefer the decoupling with separate gate resistors but is it
essential?

73 es tnx

OE3GHB
Gerhard




Am Donnerstag, den 13.01.2011, 17:50 +0000 schrieb mal hamilton:

Minto
One approach is to use a few in parallel like they do in plasma tv's but
there must then be other considerations to hinder the application.
mal/g3kev

----- Original Message -----
From: "Minto Witteveen"<[email protected]>
To:<[email protected]>
Sent: Thursday, January 13, 2011 5:42 PM
Subject: Re: LF: FET RDS

Yup that is correct. High(er) voltage fets usually have the higher RDS-on
values... Tradeoff based on physics...
I started my 500-600 Watts 500 KHz transverter with two IRFP360's in
parallel.
Later I switched to IXFH26N50 (cheaper at EUR 1 a piece and slightly

better

than the IRFP360).
The IXFH26N50 has a VDSS of 500 Volts, and a RDS-on of 0.23 Ohms and an Id
of 25A.
With two of these in parallel the efficiency is>  90%. DC supply is (max)

54

Volts.
Peak voltage on the drains is somewhere around max 250 Volts. So I might
search for Fets with a somewhat lower RDSon and a lower max voltage, but
these fets are indestructible in my setup, they survive open and
short-circuited antennas without a problem for several minutes until heat
becomes a problem.


For more info wrt my setup see www.pa3bca.nl

Regards,
Minto pa3bca (500 KHz in PA idle at the moment, alas...)




From: mal hamilton
Sent: Thursday, January 13, 2011 17:25
To: rsgb
Subject: LF: FET RDS


LF/MF
It seems to me if you are working with low V high current FETS the RDS

seems

reasonable 0.02 for example but when a High V low current device is need

the

RDS of these devices seem to be around 0.4 considerably higher.
therefore the efficiency of the amplifier will never reach the 90% plus

that

some claim.
I stripped a plasma tv recently and found banks of FETS (6 per bank) and
wondered why the application neederd so many and have come to the

conclusion

that because of the high RDS lots were required in parallel to reduce the
losses.
Maybe there are low RDS fets about that will handle several hundred volts

at

modest currents ie 10A at 1000 volts
Room for thought

de mal/g3kev