Capacitor Impedance is less than ESR?
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Posted by John KD5YI on August 9, 2008, 9:13 am
Please log in for more thread options If the two graphs are not swapped, I'm having a hard time with this http://www.cde.com/catalogs/AFK.pdf Last page, graph in the upper right compared to the graph immediately below that. My question is: How can the capacitor's impedance be lower than the capacitor's ESR? Thanks. John | |||||||||||||||||||
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Posted by Phil Allison on August 9, 2008, 9:40 am
Please log in for more thread options "John KD5YI" ** It ain't and the graphs do not say it is. You have failed to realise the scales on the LHS are **ratios** - not actual values. What the graphs show is that: 1. ESR is fairly constant above 2 kHz and depends mostly on temperature - ranging over 100:1 from -55C to +105C. 2. Impedance falls with rising frequency, but is limited by the series ESR value at any temperature. ..... Phil | |||||||||||||||||||
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Posted by John KD5YI on August 9, 2008, 10:11 am
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>
> "John KD5YI" >>
>> If the two graphs are not swapped, I'm having a hard time with this >> >> http://www.cde.com/catalogs/AFK.pdf >> >> Last page, graph in the upper right compared to the graph immediately >> below that. >> >> My question is: How can the capacitor's impedance be lower than the >> capacitor's ESR? >
> > ** It ain't and the graphs do not say it is. > > You have failed to realise the scales on the LHS are **ratios** - not > actual values. > > What the graphs show is that: > > 1. ESR is fairly constant above 2 kHz and depends mostly on temperature - > ranging over 100:1 from -55C to +105C. > > 2. Impedance falls with rising frequency, but is limited by the series > ESR value at any temperature. > > > > ..... Phil You are absolutely right. Indeed I failed to read "ratio" and took it for absolute. Thank you, Phil. John | |||||||||||||||||||
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Posted by Helmut Sennewald on August 9, 2008, 9:44 am
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> If the two graphs are not swapped, I'm having a hard time with this
> > http://www.cde.com/catalogs/AFK.pdf > > Last page, graph in the upper right compared to the graph immediately > below that. > > My question is: How can the capacitor's impedance be lower than the > capacitor's ESR? > > Thanks. > > John Hello John, You may have overlooked the meaning of the plot. Upper plot: Ratio relative to ESR @120Hz, 25° Lower plot: Ratio relative to impedance @120Hz, 25° Impedance Z = 1/(jwC) + ESR The ESR is only the resistive part(value) of the impedance. At 120Hz, the value of 1/(w*C) is much larger than the ESR. That's why the ratio in this impedance plot has suich low values at higher frequencies. Best regards, Helmut | |||||||||||||||||||
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Posted by John KD5YI on August 9, 2008, 10:12 am
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>
>> If the two graphs are not swapped, I'm having a hard time with this
>> >> http://www.cde.com/catalogs/AFK.pdf >> >> Last page, graph in the upper right compared to the graph immediately >> below that. >> >> My question is: How can the capacitor's impedance be lower than the >> capacitor's ESR? >> >> Thanks. >> >> John >
> > Hello John, > > You may have overlooked the meaning of the plot. > > Upper plot: Ratio relative to ESR @120Hz, 25° > Lower plot: Ratio relative to impedance @120Hz, 25° > > Impedance Z = 1/(jwC) + ESR > > The ESR is only the resistive part(value) of the impedance. > > At 120Hz, the value of 1/(w*C) is much larger than the ESR. > That's why the ratio in this impedance plot has suich low values > at higher frequencies. > > Best regards, > Helmut You are correct, too, Helmut. I failed to read "ratio" on the graph. Thanks. John | |||||||||||||||||||
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> If the two graphs are not swapped, I'm having a hard time with this
>
> http://www.cde.com/catalogs/AFK.pdf
>
> Last page, graph in the upper right compared to the graph immediately
> below that.
>
> My question is: How can the capacitor's impedance be lower than the
> capacitor's ESR?