I have a project to detect the presence of power on an HVAC zone valve (24VAC) by powering an existing PS2051 opto-isolator which is part of a 1-Wire data acquistion system. I have been assuming (always dangerous) that an AC power LED circuit would be appropriate for this task.
I have found a number of 24VAC powered LED circuits on the Internet including one in this document the allaboutcircuits.com library (http://www.allaboutcircuits.com/vol_3/chpt_3/12.html)
Where all of the circuits I have found become vague, at least to me, is the use of capacitors in these setups. In the circuit link above, the 24VAC does not have a capacitor, but the 240VAC does (but at least it explains that it exists to reduce the power dissipated by the resistor).
In other, similar, circuits, the implications seem to be that the capacitor is needed due to the half wave rectification which is taking place. The sizing (0.47uF to 10uF) and capacitor type reasoning is not clear.
So, if I want a high reliability circuit, will the 24VAC LED circuit from the library be satisfactory to drive an opto-isolator or does it need a capacitor? If it does need a capactor, what type and size? TIA.
Best Regards,
Mark
I have found a number of 24VAC powered LED circuits on the Internet including one in this document the allaboutcircuits.com library (http://www.allaboutcircuits.com/vol_3/chpt_3/12.html)
Where all of the circuits I have found become vague, at least to me, is the use of capacitors in these setups. In the circuit link above, the 24VAC does not have a capacitor, but the 240VAC does (but at least it explains that it exists to reduce the power dissipated by the resistor).
In other, similar, circuits, the implications seem to be that the capacitor is needed due to the half wave rectification which is taking place. The sizing (0.47uF to 10uF) and capacitor type reasoning is not clear.
So, if I want a high reliability circuit, will the 24VAC LED circuit from the library be satisfactory to drive an opto-isolator or does it need a capacitor? If it does need a capactor, what type and size? TIA.
Best Regards,
Mark