Negative Charge Pump with Ring Oscillator

In principle, the square wave oscillator doesn`t have to be a 555 timer, it could be a ring oscillator using inverters as you propose. In practice, using 4000 series CMOS logic for example, the negative output voltage produced would not be able to provide a great deal of current due to the current sourcing limitations of the IC. If the amount of current required from the negative output created is small,
Negative Charge Pump with Ring Oscillator - schematic

maybe half a mA depending upon the supply voltage, I don`t see why using CMOS inverters for the oscillator wouldn`t work. Thanks a lot! I hope it`s not too much to ask, but could you explain the operation of the (negative charge pump part of the) circuit Cenoc May 5 `11 at 19:51 Pin 3 is the output of the 555, which will be a square wave between ground and the supply voltage. When the output is high, the 22uF charges up through D1. When the 555 output goes low, the 22uF cap will discharge through the 555, through ground, the 100uF cap and D2, putting a negative voltage on the 100uF cap with respect to ground. Madmanguruman May 6 `11 at 2:20

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