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MC33078: possibility of phase reversal

Shinichi Inoue
Guru 20101 points
Part Number: MC33078

Dear Specialists,

My customer'd like to know the possibility of phase reversal.

According to the attached application note, PNP or JFET input stage may cause.

I think MC33078 is PNP input stage, is it correct?

Could you please let me know whether phase reversal will occur when input voltage is lower than the common mode voltage range?

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Guru* 93105 points

    Shinichi-san,

    The MC33078 has a conventional PNP differential input stage similar to that in the Figure 1 circuit shown in the AAJ article you referenced. Not only is there the current source off the Vcc rail, but an NPN dynamic load pair off of the V- rail as well - and there isn't any anti-phase reversal circuitry in the design. If the dynamic load for the input stage is driven into saturation by an exceedingly large negative common-mode voltage output phase reversal is likely to occur.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Guru 20101 points

    Hi Thomas,

    Thank you for your reply.

    I understand MC33078 has a possibility of phase reversal when large negative common-mode voltage is input.

    I'll share this information with the customer.

    I really appreciate your great help and cooperation.

    Best regards,

    Shinichi