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[SOLVED] Changing voltage for SMPS By DAC without neg supply for OPAMP

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Paul GRIM

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Hi all,

I am designing a programmable inverting smps.
the output of the smps will vary between o to -10V.
i chose this circuit (two OPAMP and DAC and Vref for varying my output)
inverter.PNG

but if i use this circuit, it is necessary to have negative supply for the second OPAMP.

Is it possible to return this programmable circuit without a negative supply ?

Thank you

Paul
 

FvM

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I believe you can design a circuit that uses out_n to supply the OP(s). ADJ don't need to swing below this level.
 

Paul GRIM

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Hi FvM,

Thank you for your answer.
but i have a remark, if i supply the opamp by the output voltage i inject many noise to my OPAMP.
2) the output voltage vary = supply OPAMP very !! (and the offset of OPAMP change !!)
3) is it possible to use an other solution for driving this inverter without negative supply ?

Thank's

Paul
 

BradtheRad

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if i supply the opamp by the output voltage i inject many noise to my OPAMP.

This trick can smooth the supply to your opamp. Install a resistor and extra smoothing capacitor.



2) the output voltage vary = supply OPAMP very !! (and the offset of OPAMP change !!)[/QUOTE]

If you want an unchanging supply voltage to the op amp, then a zener diode will do the job.
 

Paul GRIM

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hi brad,

thank you for your answer

the output voltage vary = supply OPAMP vary !! (and the offset of OPAMP change !!)

Actually i havn't probleme in simulation, but in practical case i fear to have a bad surprise :thinker:


Paul
 

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