I am trying to develop a design for a power supply. At the output of my design is a diode rectifier with a capacitive filter output. I've been told that I should expect to see an ESR of zero or something along those lines in my frequency response, but I'm not quite sure what that typically looks like or what that would look like in my frequency response.
Does the filter create a zero and how can I calculate the location of the zero? How would I know there is no additional poles added to my response as well? Is there some way I can simulate this to see what it looks like?
I can provide you a general schematic of the rectifier and output capacitor filter (this is the same as my design):
Best Answer
Your output filter response should basically be the 20 dB/decade response of the capacitor.
The ESR zero will depend on the number and type of capacitors you're using. It's the natural corner frequency formed by the effective ESR and total capacitance:
\$ F_z = \dfrac{1}{2 \pi \times R_{esr} \times C_{out}} \$
The gain slope will swing more positive at the zero, and you'll see the phase changing as well. You can easily use a free SPICE simulator like LTSpice IV to model the output precisely (with ESRs, ESLs, etc.) and generate a Bode plot.