LF: RE: 500kHz Classe-E

[Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>]

Hello Andy,

 

what you got looks fine for a 500W PA.

Just the on-resistance of the IRFP452 (0.4 Ohm) seems a bit high. At 10A the heat loss in the FET will be 40W, lowering the efficiency a bit. An option would be 2 devices in parallel (if the switching characteristics do not differ too much) or better running from a higher voltage (80 to 100V).

I have build a 400W class E PA for 137kHz many years ago and it worked fine ... as long as the load was more or less 50 Ohm. I found that the class E PA was much more sensitive to load mismatch than a push-pull class D PA (G3YXM design). So I decided to stick to the last, sacrificing some efficiency (85% for the class D PA, 93% for the class E PA if I remember well).

 

73, Rik  ON7YD - OR7T

 

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Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Andy Talbot [andy.g4jnt@gmail.com]
Verzonden: donderdag 6 januari 2011 10:29
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: 500kHz Classe-E

As I have all the bits available as surplus junk on the shelves, thought I would put together a QRO class-E  PA based around Alan's spreadsheet, (with mod for matching built in).

But before comitting to any particular power level / supply voltgage combination thought I'd ask what others have reliably achieved with a similar setup.

 

Starting parameters :

   Supply voltage anything from 28 - 55V adjustable.  25 A max

   PA device  - IRFP452 (have a small handful, so can allow a few to go pop)  Rated 500V,   0.4 Rdson, 14A,  190 Watts

   Drive, accurate 50% square wave from ICL7667

   Resonant Inductor -  air wound with 2mm Litz wire.

 

I reckon that at 55V 500 Watts might be a value to aim for with a single device, with the option to back off by lowering Vsupply.

But before committing to winding inductors and making parallel combination of high voltage caps, does anyone have any practical experience?   Am I aiming for too high a power perhaps.

 

Andy

www.g4jnt.com