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UCC256301: Output Voltage adjustments

Sebastian Scheiff1
Prodigy 85 points
Part Number: UCC256301
Other Parts Discussed in Thread: TLVH431

I am looking at using the UCC256301 as part of a AC/DC voltage converter. I understand that I need to change the Transformer windings ratio to make rough adjustments to the output voltage and need to adjust the resistors in the voltage divider network in the FB circuit to make fine adjustments. Is there any documentation somewhere how to adjust the resistors to fine tune the output voltage? I haven't found any documentation explaining the math. The opto-coupler is throwing me off.

Regards,

Sebastian

  • 0
    TI__Mastermind 27145 points
    Hi Sebastian,

    Thanks for your interest in UCC256301. The output voltage itself is set by the resistor divider connected to the secondary side amplifier. In the UCC25630-1EVM, these resistors are R25 and R26. The relationship is Vout*Rbottom/(Rtop + Rbottom)=Vref. So in the EVM where the TLVH431 has an internal reference of 1.24V, the equation becomes Vout*R26/(R25 + R26)=1.24V. Since you already know what your output voltage needs to be, select a value for either R26 or R25 and then solve for the other resistor value.

    The amplifier then drives the opto-coupler appropriately to maintain the mid point of the feedback divider close to its reference voltage.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 85 points
    Thanks Ben, much appreciated! For some reason it just wasn't sinking in. As I mentioned in my earlier post, the opto coupler was throwing me off.