Wednesday, April 3, 2013

compensation circuit questions

On homework 7 we were given a type 2 compensation network for problem 2 as part of a Buck voltage regulator operating in discontinuous conduction mode. As we are using this same compensation circuit for Homework 9 I have a few questions regarding the solution given on homework 7.

I have a calculated transfer function of vc/v is equal to: (sC2R2 + 1)/[sC1R1*(1+sR2C1C2/(C1+C2))].  If the pole at C1R1 is designed to be equivalent to C2R2 then (sC2R2 +1)/sC1R1 becomes 1 + w/s, an inverted pole.

In the solution, it states that "at mid-frequencies around fc, Gc(s) = R2/R1". Can anyone give me any help on where this comes from and how we determine it?

Additionally, the equation used to determine the crossover frequency where T = unity gain is given as:
1/Vm * R2/R1 * Gd0 * fp/fc = 1
where does the fp/fc come from?


UDPATE: I actually found a good paper on the Intersil site that discusses this compensation network.
www.intersil.com/data/tb/tb417.pdf

I'm still confused about the unit gain equation, and anyone who can give help on this would be appreciated.

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