LF: Re: [rsgb_lf_group] Single Stage Class-B

[Andy Talbot <andy.g4jnt@gmail.com>]

There's nothing inherently "more linear" about push pull over a single stage, given you run the same device at the same power per stage (ie half the PP level)    

'jnt

On 22 February 2016 at 18:34, Rik Strobbe rik.strobbe@fys.kuleuven.be [rsgb_lf_group] <rsgb_lf_group@yahoogroups.co.uk> wrote:

 

Hello Andy,

 

the advantage of a push-pull class B amplifier is that it it pretty linear at higher power levels.

 

73, Rik  ON7YD - OR7T

 

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Van: rsgb_lf_group@yahoogroups.co.uk [rsgb_lf_group@yahoogroups.co.uk]
Verzonden: maandag 22 februari 2016 18:31
Aan: rsgb_lf_group@blacksheep.org; rsgb_lf_group@yahoogroups.co.uk
Onderwerp: [rsgb_lf_group] Single Stage Class-B

 

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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Posted by: Rik Strobbe <rik.strobbe@fys.kuleuven.be>

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