I'm building a circuit similar to this: https://courses.cit.cornell.edu/ee476/FinalProjects/s2008/cj72_xg37/cj72_xg37/ (voltage and current sensing of a 230V line)
I'm using two HCPL-7520 isolation amps to separate the line voltage side from the low voltage side. The low voltage side will be powered from USB or an external wall-wart regulated down using a 7805, as this side will need considerable current (Arduino, etc.)
But, on the HV side, I only need a power supply to power the HV sides of the HCPL-7520's, each taking a maximum of 19 mA. So, I'm wondering, whether I can use a transformerless power supply to drive the HV side? Since the HV side also needs stable voltage, I'd use another 7805 on this side.
So, I need a transformerless power supply, stabilized with a 7805, and capable of outputting 40 mA.
What are the design considerations for such a power supply? What type circuit would you recommend? Does the 7805 consumes a significant power, which would mean that the transformerless supply would have to output more that 40 mA? The HV side of the circuit will be completely isolated from users, so there's no problem with the whole power supply circuit being considered live, as it is the case with all transformerless designs.
I'd also like to implement the circuit in a way, that the input connector could be connected either way (e.g. switching line and neutral on the input doesn't matter)