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uc3854a current sensing using transducer?

manikandan selvam
Prodigy 50 points
Other Parts Discussed in Thread: UC3854A, UC2854

Hi genius,

AC/DC boost converter with PFC controller.

Input : 180-270Vac

Output Power = 6kW

Output voltage = 400 vdc

Output Load = 15A

PFC controller chosen = UC3854a

My question is, How i sense the current from the power circuit. Can i use current transducer LEM ? If so, how to input the sensed current into the controller ... or any other method....can you give any derivations .....any paper.... i read few papers from ti ,but there is no equation for this....

then how to give the auxiliary voltage to the IC. By introducing a secondary winding across a inductor or any other method... If inductor coupled used how to calculate the turns ....

regards,

S.Manikandan.

  • 0
    TI__Mastermind 25130 points

    Dear Sir,

    I do not have enough information to tell if you can use a LEM current transducer.  The frequency response of the output signal from the transducer will in all probability be to low to use in this application and you will want a signal that is inverted and referenced to ground. I would recommend a large shunt resistor (can be lossy) or a current transformer.

    The application note SLUA146A will provide some insight into the design of the current loop even though it is written around a more complex topology. 

    http://www.ti.com/lit/an/slua146a/slua146a.pdf

    With the UC3854A you will need two current transformer one in series with the FET switch and one in series with the diode to capture the entire input current waveform. With a resistor all you need is one resistor in the return leg of the circuit. as shown in Fig. 1 of the UC2854 spec. http://www.ti.com/lit/ds/symlink/uc2854.pdf. Note that theis resistor will seee all of the input AC current so should be sized accordingly for power.

    Regards,

    John