Opamp feedack: series RC

[qolpa]

Hi all,

I have been wondering for a long time what is the purpose of series R2 C2?(see attached) The other part of the circuit is not important

I think it is some kind of filter but how can we calculate the corner freq, is it like basic low-pass or high pass RC? (1/2*pi*R*C ??)

Any help would be appreciated..

 

[FvM]

When you sketch the gain versus frequency (bode plot), you get decreasing gain (integrator behaviour) up to ω1 = 1/(R2C2),
constant gain up to ω2 = 1/(R2C1) and decreasing gain above ω2. In other words, you have two poles at 0 and ω2 and a zero at ω1.

The circuit is often used for controller amplifiers, e.g. in switched mode supplies. R2 and C2 form a PI characteristic, C1 provides an additional
high frequency roll-off above the loop transition frequency to supress interferences.

 

[biff44]

yep, what he said. The purpose of the zero at w2 is to keep the phase shift from being 180 degrees as the open loop control loop gain crosses the zero db level. Keeps the control loop from oscillating.

 

[qolpa]

FvM and biff44,

thank you, i will work on it