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LPV821: Current Sensing in No-Neutral Light Switches

Part Number: LPV821

The Application Note SNOA968A–August 2017–Revised October 2017 relating to LPV821 shows in Figure 5 an AC/DC converter supplying power to the amplifier. 

However the core of the problem in these kinds of 'no neutral' environment applications is providing the power to the electronics. In this figure an AC/DC converter is shown with a single input. In fact this will not work and it appears that there is no way to implement an AC/DC converter in this context without a neutral wire.

Is there a mistake on this diagram? where is the other AC input to the AC/DC converter supposed two come from?

Has this reference design ever been built and if so how did it work given the schematic?

I am trying to implement exactly the example provided in Figure 5 but have found no solutions anywhere for powering the electronics in a 'no neutral' environment.

Can you help?

Kind Regards


  • Hi Chris,

    No-Neutral wire switch is just a type of switch. I think that this is marketing jargon ( that is trying to confuse people, I think). The electrical circuit has to be completed in some way in order to work. The image below is the wiring differences between conventional switch and switch without neutral wiring methods. 

    Ok, there were old homes that built prior to 80's may not have neutral wire at switch box, which is safety code wiring violation now days. 

    The main reason is that smart switches require a source of power to be On all the time in order communicate with a device. 

    If you are still confused, please watch some videos in youtube.