Stefan
At this sort of measured efficiency you would need very accurate calibrated
measuring equipment.
Figures of 96% are only possible with MAGIC FETS, RDS 0.0 and PA coils with
wire resistance of 0
Measure DC input V*I (watts) on load, then RF output into a dummy load I
squared R (watts) subtract one result from the other ie loss and calculate %
efficiency.
Instrument accuracy could be out of calibration by several percent.
73 de mal/g3kev
----- Original Message -----
From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
Sent: Thursday, January 13, 2011 9:36 PM
Subject: Re: LF: Re: Re: FET RDS
> My LF 1 kW class E PA i using a single IRFP360 at > 96 % efficiency (at
> Z=R=50 Ohm of course). The driver is a ICL7667. The supply voltage is 80
> VDC. That's not a dream ;-)
>
> Stefan/DK7FC
>
> Am 13.01.2011 18:44, schrieb mal hamilton:
> > Jim
> > What you say is correct but it is virtually impossible to achieve the
90%
> > plus efficiency claimed by some. The FET required in practice is not
> > available and these high efficiencies are only theoritical.
> > I have found this in practice ie 80% if you are lucky on a good day
> > mal/g3kev
> >
> >
> > ----- Original Message -----
> > From: "James Moritz"<[email protected]>
> > To:<[email protected]>
> > Sent: Thursday, January 13, 2011 5:31 PM
> > Subject: LF: Re: FET RDS
> >
> >
> >
> >> Dear Mal, Andy, LF Group,
> >>
> >> There is a trade-off in construction of MOSFETs - basically, for a
given
> >> area of silicon, higher BVdss requires a thicker active region of the
> >> MOSFET with higher on resistance. You can reduce Rdson by using a
greater
> >> chip area, but that means higher capacitances, increased cost, etc. So
you
> >> can't have your cake and eat it.
> >>
> >> In Andy's breadboard circuit, there is a mismatch between the available
> >> MOSFET type and the available PSU voltage - the 500V BVdss is a bit too
> >>
> > high
> >
> >> for a 60V DC supply - the peak voltage in an ideal class E is 3.56 x
Vdc,
> >> perhaps you would allow 5 x Vdc for safety. 300V BVdss mosfets seem a
bit
> >> thin on the ground, so more efficient schemes might be to increase Vdc
to
> >> about 100V, or reduce it to about 40V and use lower Rdson 200V mosfets.
> >>
> >> Cheers, Jim Moritz
> >> 73 de M0BMU
> >>
> >>
> >>
> >>
> >
>
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