Current flow restrictor in an AC circuit

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Thread Starter


Joined Dec 31, 2015
Hello, this is a query I have going in one of my other posts but I thought I'd bring it out of that as it probably warrants a standalone post and apologies if I am going over old ground.

I have a circuit which is powered by harvesting a number of mA's from a 230V AC lighting circuit. As we know current can only flow in the lighting circuit when the light switch is closed, and therefore the lights illuminated, however my circuit requires power permanently so when the light switch is open the lights are off and there is no current in the AC lighting circuit. I am therefore unable to harvest any energy to supply my circuit. To add more complexity my circuit is being designed to sit in the back box behind the light switch so there is no neutral conductor available.

I'm wondering if it is therefore possible to have the AC lighting circuit permanently live but to 'restrict' the current flowing to the downstream lighting load while the lights are not required to be on. I could consume the mA I require for my circuit direct from the source and restrict the series current passing through it to the lighting load? Rather like a flow restrictor in a pipework design?

If my circuit consumed say 100mA then could I restrict the maximum current the circuit can draw to just a bit over the 100mA? I could therefore design the circuit to always be live, and therefore have a permanent connection to neutral through the downstream lights, but such that there is not enough power being delivered to the load to enable the lights to illuminate. When the lights are physically needed to be on I could bypass the restrictor and permit the full load current to circulate to the lights.

Any thoughts?
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