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AMC23C10: Why it has better power consumption than optocoupler, for zero crossing

Jade Han
Intellectual 1645 points
Part Number: AMC23C10

Tool/software:

Hello team,

I had a quick question about zero crossing & AMC23C10,

I see that there are many methods of creating zero crossing circuitry: optocoupler+diode, comparator, schmitt trigger, isolated ADC, etc.

And reading through apps note sbaa542 (link below), I see that using isolated ADC has benefit of reducing standby & off-mode power consumption, in comparison to optocoupler+diode method.

But I am not quite grasping this, why isolated ADC would have better power consumption than photocoupler, could you please explain a bit more in detail on why it would? As a NCG I am a bit new to isolated ADC, so I hoped to ask. My customer is considering using our AMC23C10 from their previous opto-coupler methods to improve power consumption, and I have a meeting with them tomorrow. I want to understand better so that I can convince them to use our solution.

Thank you in advance for your help and support.

https://www.ti.com/lit/ab/sbaa542/sbaa542.pdf?ts=1757590495822&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FAMC23C10

  • 0
    TI__Intellectual 2531 points

    Hi Jade, it really depends on the circuit and the final application. An optocoupler has a limited CTR (current transfer ratio) and for this reason, the current through the primary diode has to be relatively high under all conditions. The isolated comparator input does not sink much current but requires an external isolated power supply. 

    To have a fair comparison, I would need to see the current implementation with the optocoupler, and then would find out if the isolated comparator makes sense.

    From the appnote:

    "The circuit is used for AC line zero-cross detection in control circuits to reduce standby and off-mode power consumption."

    An optocoupler will sink current on the primary side regardless if the system is in the standby- or off-mode. The isolated comparator requires an external isolated power supply that often comes from the secondary side (MCU side). When the system is off, the DC/DC is off and there is no current flowing to the isolated comparator input (in contrast with the optocoupler). This is, however, true only if the isolated comparator is powered from the external isolated DC/DC converter. For example, if the isolated comparator uses a rectified input voltage and a zener diode, then this statement is not true anymore.

    This is how I understand it.

    Best regards, Jiri