Hello All
I am designing a circuit for a very low cost consumer product. We are at prototype stage.
AN954 from microchip is a good reference for this design.
Circuit for capacitive PSU on page 2.
The power supply is Transformerless and up to now is based on using power resistors to drop the mains voltage and feeding to a zeener to produce the +5V for a processor and also +5V/-5V for an op - amp measurement circuit.
We must have +5V and -5V for the op-amp due to the input signal we are measuring.
With a view to reducing the heat dissapation from the power resistors we are looking at changing to a capacitive power supply.
The capacitive design for this type of PSU requires the +5V to be at mains Live with circuit GND at 5 Volts less than this level. Its hard to see how to create a circuit that would produce -5V with respect to circuit GND.
This is where Im stuck. Can this be done.
Many thanks for any assistance
Denis ___________________________