#### treez

##### Advanced Member level 5

**Expression for small signal controller transfer function for "type 3" compensator.**

Please help in converting the given expression for a "type 2" compensator to a "type 3" compensator in a flyback SMPS. This concerns the application note AN57 by Power Integrations. (linked below)

Referring to AN57… equation 25, page 14 shows the expression for the small signal transfer function of the controller in a topswitch based flyback SMPS. This expression is a “type 2” compensator and corresponds to the schematic of fig 23, page 14.

If this compensator is converted to a “type 3” compensator, as in fig 26, page 15, then how should equation 25 be adjusted to produce the correct small signal transfer function? (note that converting to a “type 3” compensator just involves adding RF4 and CF2 across RF3).

AN57:

https://ac-dc.power.com/sites/default/files/product-docs/an57.pdf