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MC33063 Inverter Vout -7V, Vin 15-25V (>6V) possible?

Staffan Bruce
Prodigy 20 points
Other Parts Discussed in Thread: MC33063A

Hello,

 

We need a voltage inverter providing -7.0V 50mA. In the datasheet for the MC33063 there is an example showing almost this, but the input voltage is limited to +6.0V. Our input will be between +15 and +25V. Is this possible?

Following another thread, it seems like the important limitation is Vin-Vout, which in this case will be less than 32V (rating seems to be 40V), but are there any other restrictions?

 

Basically, can anyone please suggest the relevant changes to the schematic (Voltage-Inverting Converter, Figure 10.) in the datasheet so that it accepts a Vin 15-25V and provides a Vout of -7.0V at 50mA? Efficiency is not an issue, ripple is however (the suggested optional filter seems to do a good job though and that should be sufficient for me also).

 

Many thanks in advance!

 

Regards,

  Staffan

  • 0
    TI__Guru**** 167286 points

    Staffan,

    Yes, the MC33063A an invert 15V to 25V to -7V @ 50mA.  You are correct, the Vin - Vout is a critical value and 32V is good.
    The feedback resistors will need to be set for -7V output. The higher input voltage will likely result in larger inductance or shorter Ton.
    Start with the formulas on page 10 for voltage inverting. When calculating Ct, use figure 1 on page 5 because it is more accurate than the linear formula.

    Regards,
    Ron Michallick

     

     

     

  • 0 in reply to Ron Michallick
    Prodigy 20 points

    Ron,

     

    Many thanks for the very fast response, I will try this!

     

    Regards,

      Staffan