I'm making a special 2-wire sensor that can be power by the parasitic current that can flow in EN 61131-2 type 3 input. More info about this interface you can find here,
https://download.beckhoff.com/download/document/Application_Notes/DK9222-0909-0008.pdf The standard define at which voltage level a 24 Volt digital input should trigger.
The idea is to connect my sensor in between the +24Volt line and a type 1/3 digital input.
My sensor can consume max 2 mA and by modulating the input voltage I can send an 0 or 1.
So the summery is the following,
The digital input terminal can supply 2 mA minimum and the minimum voltage is 5 Volt. So I have 10mW of power to use for my processing and sensors. It the idle (0) state I have around 40mW.
So I have 10mW when I put a logical 0 and 40mW when I put a logical 1 on the line
Now I have a CCS811B which is a nice TVOC/eCO2 sensor. In it's low power mode it consumes around 1.3 mW average.
I checked the current consumption and it does consume for 1.5 s around 25 mA. This happens every 60 s, which that averages to the above number.
Now my problem is how to bridge the power gap. For 1.5 s I need to supply at least 50 mW.
Any one an idea?
I was thinking about a small SMT supercap but the internal resistance of those is just way to big to be usefull. Small battery is not really an option because of the limited cycles...
Currently I have a TPS62175 generating 1.8 V from the 5 to 24 V supply.