|
Anything above 70% is respectable especially if it
cost nil for components and occassional use.
de mal/g3kev
----- Original Message -----
Sent: Thursday, January 13, 2011 5:55
PM
Subject: Re: LF: Re: Re: FET RDS
If I can get 80% for 400V on 500kHz using a pair of cheap and
cheerful FETs cobbled together, 90% plus should be easy-enough by spending a
bit of time and effort on their selection.
A while back I managed greater than 85% on a 20W class E topband PA,
and that is an overall efficiency figure, including power taken by
driver stages and dropped in linear regulators.
So its hardly rocket science.
Andy
On 13 January 2011 17:44, mal hamilton <[email protected]>
wrote:
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
>
>
>
|
