type III error amplification, SEPIC

Discussion in 'The Projects Forum' started by yoamocuy, Aug 9, 2014.

  1. yoamocuy

    Thread Starter Active Member

    Oct 7, 2009

    I'm working on a SEPIC design that requires type III error amplification and am having some trouble understanding a few things. More specifically, I'm having problems understanding where exactly to place crossover frequency. From what I understand about type III error amplifiers, you are wanting to place your zeroes at a frequency that will negate the double pole at fLC, you are wanting to place your poles such that fESR and fRHP will be negated, and then you have a pole at the origin. If those poles and zeroes are all set as mentioned, is there any need to worry about where the crossover frequency falls? One doc I read suggested that the crossover frequency should be set such that it is less than 1/10 the switching frequency, less than one fifth the RHP zero frequency, and less than twice the resonant frequency but if the poles and zeroes need to negate the poles and zeros from the power system, how does one have any additional control as to where to place the crossover frequency? Are those 3 guidelines just used as a sanity check?