The circuit as shown would be unsatisfactory.

A variable (programmable I believe they call it) LM385 
precision shunt regulator would do the job at not vastly 
more cost and in a far superior manner.



        Russell

> I was thinking about regulating the Vdd using an amplified 
> diode circuit.
> Basically the input voltage could be varied between 4-7.2V 
> and I am going to
> set this circuit to 3.3V. The load is around 1-2mA. I was 
> wondering if there
> is any con about this?

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