Behaviour of transient response when PM and cross-over frequency changes

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Patrick_66

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Hello everyone, I'm currently building an LED driver using type one compensation and I simulated the output current with different phase margins and cross-over frequencies to study the response of the system. The result that I got is when the phase margin decreases the cross-over frequency increases and the percentage of overshoot as well as the time to reach transient decreases but the damping increases. Wanted to ask whether this situation is normal? If the result is correct, if possible can you explain why is this situation like this. Thank you in advance and sorry for my ignorance.
 

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Hello Sir, may I ask why my overshoot keeps on decreasing as the phase margin decreases?
Click to expand...

As phase margin decreases overshoot increases. Why yours is doing the opposite I have no clue.

What simulator are you using ? Note it seems your overshoot value is changing very little over
most of the screenshots. How is phase margin being calculated ?


Regards, Dana.
 
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Hello Sir, firstly I identify the transfer function of the flyback converter and then identify the transfer function of the compensator circuit then multiply them together to obtain the overall transfer function of the system including the PWM, flyback system and the compensator. Something like the Figures below.
 

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When cascading, in order to use simple multiplication of the transforms, they individually have to meet :


So output of each transform must be unperturbed by the loading of the next transform.
In other words the driving transform into the receiving one must be a V source ? Not
expert here.....think buffer between each stage conceptually.


Regards, Dana.
 

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Sorry Sir, I do not quite understand. I'm confused now.
 

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Each T(S) must be isolated from each other in order to use simple multiplication
of them to get overall T(s).

 

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