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I am studying a design of a fly back DC-DC converter. It is based on TL431 voltage regulator with PC817 opto-coupler. I heard that it is a popular design used. Switching PWM pulses are generated using UCC2813-1 IC. I know how the circuit is supposed to behave. However I could not understand the exact way in which UCC2813-1 operates.

I have seen its data sheet and know how pins behave individually. Can you please explain the function of pins relating one to other like the relation between REF and RC, COMP and REF, CS and COMP and how they effect overall function of IC.

I also couldn't understand the comparator symbol used for 'error amplifier' to which FB pin is connecting (inverting input) - comparator with arrow symbol in block diagram in RED square. what does arrow indicate?

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  • \$\begingroup\$ You should post a schematic. \$\endgroup\$ – sherrellbc Jul 29 '14 at 13:36
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RF and RC, COMP and REF, CS and COMP and how they effect overall function of IC.

  • RF doesn't exist as a pin so maybe you mean REF (also see below) and the use of the oscillator resistor to REF (see RC pin) ensures the RC oscillator frequency is kept at a fairly constant frequency irrespective of power supply changes or variations.
  • RC is for placing a resistor and capacitor for creating an oscillator - read the data sheet page 6 for precise detail
  • COMP is the comparator output and again the data sheet is quite useful - the symbol is a triangle with an invert circle on one of the inputs. This is equivalent to an op-amp type symbol with a "+" on the non-inverting input and a "-" on the inverting input.
  • REF - REF/2 (half the voltage of REF) is used as the comparator input for comparing the feedback voltage with. When normally running, the fed-back voltage will nominally be the same level as REF/2

To go into much more detail is probably going beyond the bounds of EE's question and answer format. This circuit might also explain things a little better: -

http://circuits.datasheetdir.com/66/UCC28C40-circuits.jpg

It's a very similar device to the one you have specified.

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