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# UC2854B-EP: How to calculate Rsp resistor using current transformer with positive output

Part Number: UC2854B-EP

In this document on page 16 figure 11.
I'm not able to find how to calculate the value Rsp?

Is the resistor Rsp the same value as Rs?

• Hello Ricardo,

I will look into it and see if we have this information.

Thanks,
Kyle
• In reply to Kyle Rakos:

Hey Ricardo,

Rsp will have a similar calculation to Rs in figure 10.

Figure 11 simply shows how to implement a similar circuit to figure 10, but there needs to be two resistors instead of one when there is a positive output.

I don't have the information from the design, so I don't know how useful this will be, but I imagine the calculation for you will look something like:

Vsp = Rsp*Ipk (picking Rsp to be small to limit power dissipation through it)
Rpk2 & Rpk1 found by creating current divider between Vsp and Vref to create 0 V for PK LMT.

Rsp will simply be what you pick for Vsp/Ipk (Where Ipk is what you wish the peak current to be).

Thanks,
Daniel