As shown in the figure below, TL431+PC817 is used to build a type III compensation network, and the Baud diagram of the compensation network is simulated. TL431 uses the SPICE model download from TI's official website, and PC817 uses the ideal current control current source instead
The Type III network is inverted Phase amplification and accompanied by an initial pole, so the initial phase should be -270° or 90° ahead. However, the phase waveform seen through simulation has offset at the low frequency, which is different from the compensation network built by conventional OPA or OTA. What is the principle?
As shown in the following figure, it is a simple Bod diagram simulation of Type III compensation network based on OPA, and the phase at the low frequency is basically not too large offset, compound expectations
The above phenomenon of low-frequency phase offset occurs in both type I and Type II compensation networks. When the frequency increases to about 10Hz, the phase of the TL431 compensation network will reach the expected +90°/-270°. What is the principle of this phenomenon? Is it due to the frequency characteristics of TL431 itself?
