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Shunt Capacitor on ClassE




 
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Author Topic: Shunt Capacitor on ClassE  (Read 6512 times)
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yb0djh
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« on: September 23, 2007, 10:49:47 PM »

Hi All

I m new in class E. I just finished to producing 200 ++ watt of RF at 80 meter using IRFP460, now is in progress to tune up the PWM mods.

I m wondering how to calculate the C Shunt. First question is do we include the Coss into the calculation? For example in the calculation we found Cshunt is 1300 pF. Knowing that the Coss of IRFP460 is 870 pF, so the Cshunt will be 1300 - 870 pF = 430 pF. Am I right?

Thank you all

73s de yb0djh
Agus HY
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WA1GFZ
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« Reply #1 on: September 24, 2007, 08:25:23 AM »

Also consider the case to ground C of about 100 pf. You should see the peak drain voltage about 3.5 times VCC when you have it right.
You want to keep the peak voltage well below the part voltage rating
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KF1Z
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Are FETs supposed to glow like that?


« Reply #2 on: September 24, 2007, 08:02:35 PM »

What Frank said....
Plus, I'd say start with the higher value, and subtract C as needed......

Don't be worried about getting it exactly right the first go at it....


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yb0djh
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« Reply #3 on: September 24, 2007, 09:41:54 PM »

Also consider the case to ground C of about 100 pf. You should see the peak drain voltage about 3.5 times VCC when you have it right.
You want to keep the peak voltage well below the part voltage rating

Thanks Frank for responding my topic

My class E configuration is balance using one irfp460 each leg. I started with 1000 pf (10x100pf @ 1kv) each leg and i reduce it one by one until no capacitor. Smaller capacitance will make voltage signal become 'thin' and higher peak, 300 pf is a good number, voltage drain become decrease, wider and rounded before touching 0 volt.

The idea of my topics is to increase the safety factor by paralleling 2 or more FET per leg. But little pessimistic by knowing the high C oss (870pf) of IRFP460. In Jakarta especially, is hard to find FQA11N90

73s
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yb0djh
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« Reply #4 on: September 24, 2007, 09:53:05 PM »

What Frank said....
Plus, I'd say start with the higher value, and subtract C as needed......

Don't be worried about getting it exactly right the first go at it....


Thanks for your advice. Yes, i did it. and i found 300 pf is a good value.

I need more predicted result since i have experience bursting 10 or more FET in flame easily with higher capacitance. With the higher capacitance, the Drain current is high but RF output is low.

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WA1GFZ
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« Reply #5 on: September 25, 2007, 09:08:49 AM »

Yes, excessive C will hurt efficiency.
The IRF460 has high C so not sure how hard you can push it.
the 11n90 we usually run 50 watts carrier per device alowing 150% positive peak on AM. This is due to the 1 ohm RDS on. It will work above 50 watts but it will hurt efficiency. Also we try to keep the peak drain voltage below 50% of the drain voltage rating for plenty of safety factor. You should be able to get 90% efficiency.  frank
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Tom WA3KLR
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« Reply #6 on: September 25, 2007, 09:43:13 AM »

Selamat pagi,

Below is pictured an Excel spreadsheet file that calculates the component values for the basic single-ended Class E Power Amplifier stage.

I have a second file which is a variation of my original spreadsheet.  Stu, AB2EZ, made the modified sheet which adds a step-up transformer and some more notes on the tank inductor Q.

This site does not accept the .xls file directly.  What is shown here is a pdf example of the spreadsheet. 

* Update 9/25 10:12 p.m.
* To download the .xls files, you can click on the links now listed 2 posts below this post.
* Thanks to Steve WB3HUZ and the amwindow.org resources!

* ClassE_PA_design4c.pdf (16.39 KB - downloaded 289 times.)
* AB2EZmodClassE_PA_design4c.pdf (17.23 KB - downloaded 498 times.)
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
Tom WA3KLR
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« Reply #7 on: September 25, 2007, 09:45:20 AM »

Another board just for Class E is:

http://classe.monkeypuppet.com/

This site is hosted by Steve WA1QIX.
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
Steve - WB3HUZ
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« Reply #8 on: September 25, 2007, 08:49:21 PM »

The Excel spreadsheets from Tom and Stu are available for download on The AM Window Website at the links below.


http://www.amwindow.org/tech/excel/ClassE_PA_design4c.xls

http://www.amwindow.org/tech/excel/AB2EZmodClassE_PA_design4c.xls
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