Switched Capacitor Voltage Inverter

Voltage inverter implemented using MOSFETs as switches and capacitors as charge reservoirs. First capacitor is initially connected to a voltage source to charge up to 5V. Then the switches (MOSFET) flip to disconnect the first capacitor from the power supply to the second capacitor who then discharges into the 2nd cap. till it reaches an equilibrium charge distribution. The 2nd cap has been grounded in such a way that a negative voltage is seen at it’s other end w/ ref to ground. Then the switches flip again to re-connect the 1st cap. to the power supply to charge. Then the switches flip again and process repeats itself until the second cap reaches (closely approaches) max voltage 1st cap. gets charged to. A square wave from 6V to 0V with period of 2ms (500Hz) is used to continuously switch MOSFETs on and off. This produces the effect of a voltage controlled switch. The first capacitor is actually hooked up to a current source when it is charging to ensure that it charges to 5V before the switches flip. Remember the IV relationship of a capacitor - which effectively states dV_c/dt = I_c/C. So more current and smaller capacitance indicates faster charge up to 5V. In real world you will need to check max voltage rating of capacitor, so don’t change C too drastically. At the output, a peak detector (diode and capacitor) present to smooth out ripples as MOSFETs are not perfect switches; hence, the second cap. actually gets discharged into the first cap. to some degree as well. Was thinking of adding a voltage regulator after the peak detector but the one I had in mind involved a BJT and OPAMP output to connected to it’s base. And for such topologies, I have noticed that the simulator cannot find a solution. Hence, I’ll look into other topologies later. But here is the product for now. It produces a approx. -3.3V from 10V.

published 1 year ago