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PMP20183: PMP20183 Voltage modification

Part Number: PMP20183
Other Parts Discussed in Thread: LM3481


I was looking for a design to supply 180 V at low current, and PMP20183 topology looked like a good candidate. How can I tweak this design to bring the voltage down a bit? I think I should just have to decrease the value of R7, but I am not sure.


  • Hello Charles,

    the error amplifier input is at pin 4, FB = feedback, so the output voltage could be adjusted by the voltage divider
    R100 + R3 and R8; by the virtual short circuit across error amplifier input reference voltage is applied across R8.
    Vfb of LM3481 is 1.275V, applied across R8 6.34k.

    Typically we avoid to modify the high side resistors not to modify the loop gain.
    At output voltage 180V the voltage across high side resistors will be (180V-1.275V) / (487k + 499k) = 181uA;
    so your needed low side resistor is 1.275V / 181uA = 7.03k, go for R8 = 6.98k Ohm.
    This will result in output voltage 181V.

    Would recommend to limit voltage across resistors <100V, so please use two high side resistors as shown at schematics.
    Please be careful working on that design, you are dealing w/ HIGH VOLTAGE.

    Best regards, Bernd