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ISO1211: ISO1211 AC detection

Kevin Huang8
Genius 3825 points
Part Number: ISO1211

Hi Team,

For ISO1211 AC detection design, is the output level a steady state DC signal?

  • 0
    TI__Guru 54655 points

    Hi Kevin,

    Thank you for reaching out.

    If you apply a sinusoidal waveform at the bridge rectifier input, ISO1211 gets triggered at its VIL and VIH input thresholds and produces a rectangular waveform at the output. Hence, you will see rectangular waveform in sync with the sinusoidal waveform. Let us know if anything is not clear, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 20 points

    Hi Koteshwar Rao ,

    Thank you for your kind support,

    Actually,We use ISO1211 for AC 220V detect function in our product design ,

    and we refer circuit as below : 

    Q1 : If we want the ISO1211 output is stable DC voltage level , could I adjust Cin cap value ?

    Q2 : What's point A's voltage level ?

    Thanks a lot.

  • 0 in reply to Rick Liu
    TI__Guru 54655 points

    Hi Rick,

    Thank you for sharing additional details of your requirement.

    1. Yes, if your intention is to produce a HIGH at the output whenever the AC signal is present and go to LOW when the AC signal is absent then you can achieve this by adding a bulk cap for filtering.
      1. CIN is added as a noise filter to filter if there is any noise at the input and this cap can be of a small value like 1nF.
      2. For filtering AC or pulsating DC to convert to a steady DC, you would need a bulk cap with much higher value like 10µF or higher. This capacitor should be added right after the diode bridge and before any other components. In this case, just before the resistor RSHUNT.
      3. Since the bulk cap value is large and its job is to maintain a steady voltage, it can take a long time for it to discharge when the input AC is removed. If this time is critical then you can play with the bulk cap value and find the value that works best for both steady DC and reasonable discharge time.
    2. This is device's threshold which is fixed and specified in the datasheet as thresholds for RTHR = 0Ω. Please see below snapshot from datasheet for these thresholds.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 20 points

    Hi Koteshwar Rao ,

    Thank you for quick reply and suggestion ,about this bulk cap ,I have two question need make sure   :

    Q1. The capacitor rated voltage: 

    In refer circuit ,the input AC 220V to bridge rectifier output to DC voltage level ,

    below chart's blue line is maybe in DC 220V input voltage ,

    The Vsense voltage is 50V ,so could I make sure the bulk voltage is 50V above ?

    and ,In our current design ,the CIN (C420) is 100V  ,is it enougth ?

    Q2. The capacitor type :

    Could I select MLCC for this bulk cap?

    Thank you for your great support.

  • 0 in reply to Rick Liu
    TI__Guru 54655 points

    Hi Rick,

    Thank you for seeking additional clarification. Please find my inputs below, thanks.

    1. Yes, the capacitor doesn't need to be rated for 220V as it only expected to see voltage of upto 50V and the device VSENSE pin is also rated for 60V. Hence, both the bulk capacitor and CIN only need to support 50V.
      1. Please note that the capacitor actual values derate more than 50% at their max ratings. i.e., a 100V rated 10µF can actually have a value of 5µF or below when applied with 100V. For more details, please refer to the capacitance vs voltage curve in capacitor datasheet.
      2. For this reason, you can either choose a capacitor with double voltage rating or double capacitance than needed.
    2. Yes, MLCC should be fine.


    Regards,
    Koteshwar Rao