I'm practicing a design of a type 3 compensator for a voltage mode buck-boost converter, so I went through the book entitled "Switch mode power supplies Spice simulation and practical design"
The topology used for calculations of the different components of the compensator is shown below (Extracted from the book)
The specifications are as follows:
- Vinmin=10v (minimum input voltage).
- Vinmax=15v (maximum input voltage).
- Vout=-12 (Regulated output voltage).
- Fs=100kHz (Switching frequency).
- Fc=5kHz (Crossover frequency, chosen by the author to make the RHPZ after that frequency).
- Iout=2A (maximum output current)
- Rload=6ohm (DC load resistor)
I have followed all the steps given by the author but I failed to find the same values found to the compensator component. The method used to place the poles and zeros of the compensator is the manual method and not the K factor method. So the author proposed the following:
From the Bode plot, we can see that the required gain at 5 kHz is around -10 dB worst case.
To cancel the LC filter peaking, place a double zero close to the resonant frequency, 600 Hz
Since the zero occurs after the crossover frequency, we can place a first pole at 7 kHz
Place a second pole at one-half of the switching frequency, to force the gain to further roll off, 50 kHz.
Using the manual placement method described in Chap. 3, evaluate all the compensator elements.
R2 = 18.6 kohm R3 = 456 ohm C1 = 15 nF C2 = 1.3 nF C3=7 nF
When I apply, the equation encircled in red in the figure, I come out with a different value for R2. I found R2=1.8kohm but the author finds R2=18k ohm and since C1 and C2 values depend on R2, so my compensator is not good and I do not get a sufficient phase margins.
Please can anyone ensures to me the value of R2 and does the equation encircled in red correct ?