# Slope Compensation for UC3825

Discussion in 'General Electronics Chat' started by Fethiyeli, Jan 20, 2014.

1. ### Fethiyeli Thread Starter Member

Mar 16, 2013
31
0
Hi. I am confused at slope compensation for UC3825. In application note of UC3825, normal sense resistor has been used but i need to use current transformer because of high primary current. In formula in application note, sense resistor has been used for slope compensation but there is no sense resistor in case of using current transformer. I only saw a resistor at output of the current transformer in book. So how can i find sense resistor in order to use for calculation ? Should i really need it ?

and What is the best way to apply feedback ? I read Basso's book but according to this book, i need to use Spice but it is really hard to simulate some circuits i think. and second book i have read is power supply cookbook but this one calculates the feedback as not accurate as Basso's book. So, what is the best way to calculate and plot feedback gain, etc ?

Last edited: Jan 20, 2014
2. ### crutschow Expert

Mar 14, 2008
13,508
3,385
A current transformer does need a sense resistor (that's the output resistor you saw). It's just changes in value by the turns ratio of the current transformer.

Spice may be somewhat difficult to use but it is very useful in understanding and optimizing the circuit.

Fethiyeli likes this.
3. ### Fethiyeli Thread Starter Member

Mar 16, 2013
31
0
Thnx a lot dude.

4. ### #12 Expert

Nov 30, 2010
16,705
7,355
crutschow is too old to be called, "dude".

5. ### Fethiyeli Thread Starter Member

Mar 16, 2013
31
0
May i ask final important question ? how do you optimize your circuit with spice or Pspice or OrCAD ? They're all the same you know. OrCAD has UC3825 IC. I just know using OrCAD, ı saw that there are some average or other models for optimizing the circuits. But i dont know how to do these models in OrCAD, do you know any website or resource that can help me for these models ? I really learn how to optimize my circuits via OrCAD. I dont know how to model them. I just know adding components and other things.

6. ### #12 Expert

Nov 30, 2010
16,705
7,355
My problem exactly. Can't seem to find time to learn the simulators.

7. ### Fethiyeli Thread Starter Member

Mar 16, 2013
31
0
When i put and connect all components to OrCAD, there is always an unconnected pin and if it is unconnected, OrCAD gives an error. but i dont know how to fix it. Even i fix that problem, i always encounter with a annoying floating error. Also i dont know how to implement ferrite core transformer for SMPS in OrCAD.

Last edited: Jan 20, 2014