SG3524 is a single chip pulse width controller (SPWM) circuit. Its ninth pin is the output of the error amplifier, which is mainly used for phase compensation of the error amplifier. Several practical application circuit diagrams are found. Generally, nine pins are fed back to the 1 pin (noninverting terminal of the error amplifier) through the resistance-capacitance circuit, which is AC noninverting feedback and plays an accelerating role. The RC time constant is large, which makes the error amplifier have the shaping function similar to Schmidt circuit.

In figure 1, pin 9 also has the function of DC level compensation, which is used to compensate the DC offset of pin 2 (inverting terminal of error amplifier, sampling input) and adjust the zero offset of output waveform. In Figure 2, pin 9 is a simple AC noninverting feedback.

Here are two application diagrams in the data sheet. The former uses 9 pins for overcurrent protection, while the latter only does phase compensation and delays the signal or is called low pass.

The nine pins of SG3524 are generally connected to the circuit in the same way as other pins, such as soldering to the circuit board or inserting IC? There are no special requirements for sockets, and there will be no adverse effects.