Hi Everyone,

I am having a difficult time of understanding loop compensation. Why do we need loop compensation? We do set the operating frequency for converter. Why do we care about the frequency response for other frequencies? Why is the phase and the gain margin important? I am new to electronic. Is it possible for you to explain it in a dummy way? Thanks

 

I believe this was already answered in another forum.

 

Keywords:
* Form of the step response (how much overshoot?) of a closed-loop system
* Stability of a closed-loop system
I think the whole story cannot be explained/discussed in such a forum.
You should try to consult some textbooks or other "serious" knowledge sources.

 

Hello there For PWM duty cycles above 50 percent, all current-mode control buck converters require a linear ramp (i.e., slope-compensation) to avoid sub-harmonic oscillation. And higher duty cycles require greater slope compensation. Using nonlinear compensation circuitry (such as found in National's LM20xxx series, for instance) offers a better solution because it optimizes the stability of the regulator device over the entire output voltage range.
In the typical fixed-frequency DC/DC converter, a PWM pulse controls the time during which the inductor is energized within each switch period. CMC, in the simplest terms, compares a slow moving output-voltage error signal to the relatively fast changing inductor current. The inductor current sense signal can be converted to a 'sense' voltage signal for a voltage comparator based CMC design, a method commonly described in the literature. Alternatively, the error signal can also be converted to a current so that the regulator's three signal currents (error or control, current sense, and slope compensation) can be summed at a common node for comparison

 

A switch mode power supply need to have a feedback control circuit to regulate the power supply in case of input voltage (Vin) or load (I load) current change. Duty cycle will be self adjusted to maintain a regulated voltage when Vin or I load change. The power section combined of FET, Inductor and Capacitor which would introduced a transfer function of a fix gain and a second order resonant frequency by LC filter circuit. When feeding back the output voltage through an inverting gain, the system will be oscillated be cause of the almost -180 phase shift of output filter LC combined with -180 phase shift of the inverting op-amp. The total is -360 degree phase shift will cause the system oscillates in a closed loop circuit mode. Therefore, the compensation network need to be design to bring the total phase shift above the -360 degree threshold to avoid the system instability. Hope that answer your question.

 

This is worth a read.
https://www.ti.com/seclit/ml/slup340/slup340.pdf

 

it possible for you to explain it in a dummy way

This is worth a read

Absolutely 100%