[Amps] HT 57 blocking cap ratings?

[Karl-Arne Markström]

No.

The RF current ratings of capacitors are derived in two ways, one is from the heating from 
dielectric and resistive losses in the capacitor, 
and the other is derived from the allowable peak voltage
over the capacitor, computed as Imax = 1/SQR(2)*Vmax/Xc. 

This maximum current is frequency dependent, and decreases with frequency, as Xc increases.

As the dielectric and resistive losses increase with frequency, the capacitors should be derated.

For a look of how this looks in practice, take a glance at the graphs in:

http://www.morgan-electroceramics.co.uk/pdfs/discrf10kv.pdf    

It would be reasonable to assume that a frequency dependence between 1/f and 1/f**2 can be applied for limited frequency excursions, implying a maximum thermally limited current on 50 MHz of between 8 and 4 RMS amperes for the HT57 capacitor. 

This should be sufficient for any 50 MHz amateur PA that I can imagine...

Hope this helps and 73/


----- Original Message ----- 
From: "Neil Carr G0JHC" <g0jhc at blueyonder.co.uk>
To: <amps at contesting.com>
Sent: Saturday, December 04, 2004 9:08 AM
Subject: [Amps] HT 57 blocking cap ratings?


> I note the HT57 (N750 series 200pf 15KV) has a max current rating on their
> web site of 12amps at 10MHz and 15 amps at 30MHz, data is based on not
> exceeding the max rated 15kv.
> 
>  
> 
> Does than mean their current handling is much great at, for example 4kv? And
> has anyone any data on their current handling rating at 50MHz? 
> 
>  
> 
>  
> 
> Any info appreciated.
> 
>  
> 
> 73 Neil G0JHC 
> 
>  
> 
>  
> 
>  
> 
> 
>  
> 
>  
> 
>  
> 
>  
> 
>  
> 
>  
> 
>  
> 
>  
> 
>  
> 
>  
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps