I'm a student. Now, I am learning to use LM5030 IC to design a Push-Pull converter. So, I read LM5030's datasheet and can not understand the function of COMP pin (Pin 3). The red line is Feedback circuit, input its connect to VOUT, output its connect to COMP pin. enter image description here Following the info in the datasheet, it's said: " The comparator polarity is such that 0 V on the COMP pin will cause a zero duty cycle". The duty cycle is to switch on/of 2 MOSFET. And in above figure, the output of the feedback circuit will make COMP = 0 when VOUT > 0, it means the duty cycle for 2 MOSFET will be zero.
That makes me can not understand. Did I miss something?

P.S: LM5030 datasheet

  • $\begingroup$ Is VOUT same as VCC in the diagram? $\endgroup$ – Mahendra Gunawardena Dec 6 '19 at 16:29
  • $\begingroup$ Yes. I edited it. $\endgroup$ – Thanh niên Yên Bái Dec 7 '19 at 1:35
  • $\begingroup$ There are two COMP in the above circuit. Pin 3 of LM5030 and Pin 4 on LM3411. Pin 3 of LM5030 is an input/output pin. Can you please clarify this in your questions? $\endgroup$ – Mahendra Gunawardena Dec 7 '19 at 12:39
  • $\begingroup$ My question is on Pin 3(COMP) of LM5030 as I mentioned on the title. $\endgroup$ – Thanh niên Yên Bái Dec 11 '19 at 1:23

As indicated in LM5030 datasheet COMP is output to an error amplifier.

The circuit for the LM3411 is as follows

enter image description here

The COMP output from the LM5030 is an input to the LM3411 which is an precision secondary regulator.

The LM3411 is a low-power fixed-voltage (3.3 V or 5 V) precision shunt regulator designed specifically for driving an optoisolator to provide feedback isolation in a switching regulator.

  • $\begingroup$ Thank you. But the point is: VCC = 3.3V => V at pin 1 of U2 = 3.3V (5V) = > Vcomp of LM5030 = 0. When Vcomp = 0V, duty cycle for 2 MOSFET will 0%. $\endgroup$ – Thanh niên Yên Bái Dec 5 '19 at 13:58

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