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AFE3010: Switch: Relay or Breaker

Jack Shen2
Expert 4015 points
Part Number: AFE3010

My customer is designing a thermoStats product and needs to pass the UL943, so they will need to use AFE3010 for the certification. They have a question about the switch. 

With their max load requirement ( 16V/3800W @ 240Vac or 16A/1900W @120Vac), they are seeking the suggestion of should they use a relay or a breaker? Thanks. 

  • 0
    TI__Mastermind 26730 points

    Hey Jack,

    Are you referring to the load switch, which is responsible for opening the load and disabling output power?

    I don't know if either option is correct. I have only seen the circuit be broken with a mechanical disconnection high voltage comparators. So AFE3010 activate an SCR, which pulls high current through a solenoid, and this actuate a mechanical motion to make a disconnection.

    I am not aware of any UL 943 requirements that limit the choice of using a relay or breaker, or both to open the load switch, but if these options are permitted, the AFE3010 could work with both.

    Keep in mind that the device has a periodic SCR self test every 3 seconds (SEL=GND). The self test is specifically designed for the SCR pin to drive a SCR that is connected to the HOT line (via a solenoid). Thus if you do not use an SCR (and rather a relay or breaker), then customer will need to disable the SCR self test by floating the SEL pin.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    TI__Expert 4015 points

    Thanks for the reply, Peter. 

    Yes, I was referring to the load switch. I am not familiar GFCI application. The UL943 did not limit the choices. It was just that the max load requirement was 16V/3800W @ 240Vac or 16A/1900W @120Vac for the thermostats application, and we thought the load switch cannot handle it, but I guess it is different path, right. 

  • 0 in reply to Jack Shen2
    TI__Mastermind 26730 points

    Hey Jack,

    The AFE3010 is not a load switch, nor does it contain a load switch. The load switch is just a general term for the disconnection/connection of the electrical/mechanical connection of line to load. It could be a relay IC or some electromechanical contraption. No matter what the load switch is, it must of course be able to withstand the rated current and voltage you mention.

    The AFE3010 was specifically designed to open a load switch via by turning on a SCR (silicon controlled rectifier) and pulling high momentary current through a solenoid. The things that happen from when solenoid is energized to when load switch is opened and outlet is disabled, is up to the engineers designing the system.

    Now if engineers want to use the SCR active-high signal to control a relay (that is acting as the load switch), then this should be possible. However, I cannot confirm whether this design will adhere to UL 943 requirements. Additionally, some features with the device might not be available such as the SCR self test procedure. If need be, the SCR self test can be turned off by floating the SEL pin.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    TI__Expert 4015 points

    Thanks for the explanation. 

    One more thing to check with you and that is the max load (16V/3800W @ 240Vac or 16A/1900W @120Vac). We should base on the max load of the application to choose whether to use a load switch or a relay. However, just like what you have mentioned, if relay is chosen, then we need to check if the engineer wants to use SCR active-high signal control or not, right.   

  • +1 in reply to Jack Shen2
    TI__Mastermind 26730 points

    Hey Jack,

    The signal from SCR pin driver should ultimately be used to latch open a load switch/relay/disconnect power and prevent someone from being shocked per the UL 943. Now how the engineer wants this to translate this signal from SCR pin to the disconnection of power is completely up to the engineer. TI recommend in the datasheet to use SCR pin to activate an SCR to pull current through a solenoid, which will break open the power, but if there is another way/mechanism to open the load (and also is compliant with UL 943), then the engineer can pursue this route.

    As for the max load, yes. Whatever load switch is chosen (and also conducting, high-voltage metals, and components, etc.), they all must be able to withstand the max rated load over all system variables (line voltage, current, temperature, vibration, etc) or else system will probably blow up. These are system-level design considerations that have no effect or dependence on the AFE3010.

    Sincerely,

    Peter