[SI-LIST] Re: Why PDS impedance exceeds target impedeance in low frequency less than 1kHz is OK ?
- From: olaney@xxxxxxxx
- To: icermail@xxxxxxxxx
- Date: Mon, 3 Mar 2008 21:32:50 -0800
On Mon, 3 Mar 2008 20:33:34 -0800 (PST) icer world <icermail@xxxxxxxxx>
writes:
> It's said that PDS impedance exceeds target impedeance in low
> frequency less than 1kHz is OK , can anyone give me some
> explains?Thanks!
>
>
Below 1 KHz, you are in the bandwidth of the power supply regulator loop.
By holding the voltage constant, the regulator acts as a very low
impedance (z<<1 ohm). If the supply has remote sense leads, you can use
those to compensate for the voltage drop in the feeding cable, making the
regulated point be at the PCB. At audio frequencies, the wavelengths are
so long that the PCB is just an itty bitty stub, and the PDS impedance is
dominated by supply regulation and by copper resistance, not by the
distributed values at HF that are the nominal focus of this forum.
Orin Laney
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