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Date: Mon, 22 Feb 2016 17:31:11 +0000
Message-ID: <CAA8k23SYMh9+5p_N78JNQ8fJWgmWvXi=M2m6dTNt6pWbomO7sw@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org, rsgb_lf_group@yahoogroups.co.uk
Subject: LF: Single Stage Class-B
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Whilst out walking and pondering, as one does....

There are hundreds of designs out there for  linear power amps using FETS.
They all use a similar design, push-pull with centre tapped ferrite cored
transformers at input and output, often with resistive feedback - and all
broadband.   The design is so standard it's become tedious ... and as I
don't do tedious, it made me think:

Back in days of yore when those big bottles ruled the roost ,  apart from a
few designs for UHF, they were all single ended.

So, why not a single ended MOSFET amp (for single band operation)?   We're
used to seeing single device  for class-E, where the tank circuit does much
of the waveform cleaning, and reduces the low pass filter requirements.
So what's wrong with a tank-based  design for class-B?

A single ended amp can even be made ferrite free (although a final stage DC
feed choke would no doubt benefit from it).   Apart from a few very low
power designs, I don't recall seeing any designs for single band ferrite
free linear amps using power MOSFETS.
Only major downsides I visualise is that load resistance at the device is 4
times lower for the same Vdd and Pout , and device dissipation is doubled

Has no one ever bothered, because broadband transformer push-pull is so
straightforward?
Has a trick been missed?

Andy  G4JNT

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<div dir=3D"ltr"><div>Whilst out walking and pondering, as one does....</di=
v><div><br></div><div>There are hundreds of designs out there for =C2=A0lin=
ear=C2=A0power amps=C2=A0using FETS.=C2=A0 They all use a similar design,=
=C2=A0push-pull with centre tapped ferrite cored transformers at input and =
output, often with resistive feedback - and all broadband.=C2=A0=C2=A0 The =
design is so standard it&#39;s become tedious ... and=C2=A0as I don&#39;t=
=C2=A0do tedious, it made me think:</div><div><br></div><div>Back in days o=
f yore when those big bottles ruled the roost ,=C2=A0 apart from a few desi=
gns for UHF, they were all single ended.</div><div><br></div><div>So, why n=
ot a single ended MOSFET amp (for single band operation)?=C2=A0=C2=A0 We=
9;re used to seeing=C2=A0single=C2=A0device=C2=A0=C2=A0for class-E, where t=
he tank circuit does much of the waveform cleaning, and reduces the=C2=A0lo=
w pass filter requirements.=C2=A0=C2=A0=C2=A0 So what&#39;s wrong with a ta=
nk-based =C2=A0design for class-B?</div><div><br></div><div>A single ended=
=C2=A0amp can even be made ferrite free (although=C2=A0a final stage=C2=A0D=
C feed choke would no doubt benefit from it).=C2=A0=C2=A0 Apart from a few =
very low power designs, I don&#39;t recall seeing any designs for single ba=
nd ferrite free linear amps using power MOSFETS.=C2=A0 </div><div>Only majo=
r downsides=C2=A0I=C2=A0visualise is that=C2=A0load resistance at the devic=
e is 4 times lower for the same Vdd and Pout , and device dissipation is do=
ubled</div><div><br></div><div>Has no one ever bothered, because broadband =
transformer push-pull is so straightforward?</div><div>Has a trick been mis=
sed?=C2=A0=C2=A0 </div><div><br></div><div>Andy=C2=A0 G4JNT</div><div><br><=
/div><div><br></div></div>

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