DIY Smart Dimmer with Power Monitoring: Need safety tips.

[johm]

Hello, low power design enthusiast here.

I am working on a mains-connected project consisting of an ST microcontroller, a digitally controlled TRIAC+IGBT based AC dimmer and a power meter IC. Basically I am stitching together two reference designs (STEVAL-ILD004V2https://www.st.com/resource/en/user_manual/um1908-stevalild004v2-leadingedge-dimmer-stmicroelectronics.pdf from ST and CRD5436PM https://statics.cirrus.com/pubs/rdDatasheet/CRD5463PM_RD2.pdf from Cirrus Logic). The design intent is to have a dimmable light socket with embedded power metering, for domestic use.

Which nodes on the dimmer circuit have AC mains voltage?
Can I use the same ground across both designs and the power supply? It looks like ground has AC voltage as well with respect to earth (it is not isolated).

I have attached snapshots of the power supply, dimmer circuit and power metering circuit (a 99 % copy from the reference designs). The microcontroller is powered from 3.3 V. I want to be sure of the above questions before feeling safe about plugging the design onto real AC mains.

Hopefully you can clarify my confusion. Thank you.

[moffy]

It is a very confusing circuit to evaluate, the best I can see is that you have a controlled bridge rectifier with two SCRs and an IGBT inserted into it somehow, the use of 'GND' everywhere when I don't think you mean mains ground is confusing. I would use the term 'GND' only to refer to mains ground and either 0V or some other name for non mains ground nets to avoid ambiguity.

[Phoenix]

A block diagram of what you're trying to achieve would help.

[NiHaoMike]

I don't see any advantage of using both an IGBT and a SCR in that application. You could instead use a pair of back to back IGBTs or MOSFETs. Reference the circuit to the middle of the two MOSFETs or IGBTs and you'll find that you can put the shunt right there.
Try these for design ideas: https://www.sound-au.com/project157.htm https://www.sound-au.com/project201.htm

[johm]

Here's a simplified block diagram of the funcionality expected. The meter IC, CS5463, is powered from 5V0 and 3V3 generated from the AC/DC brick and linear regulators. The microcontroller uses 3.3V only. The unregulated 12V are needed for the IGBT section of the dimmer. The IGBT section is used to limit the inrush of current when the SCRs are triggered, hence reducing the need for a bulky inductor.

[NiHaoMike]

The IGBT section is used to limit the inrush of current when the SCRs are triggered, hence reducing the need for a bulky inductor.

That doesn't make sense, IGBTs are generally much faster than SCRs. Inrush control is done by ramping the output.