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TLV1811: Polarity protection

ArTzy
Genius 15779 points
Part Number: TLV1811
Other Parts Discussed in Thread: LM9061, TLV1812

Hi Experts,

Seeking your assistance on this query from Cx:

Customer would like to implement a ZCD (https://www.ti.com/lit/an/snoa999/snoa999.pdf) using TLV1811 comparator. See attached circuit:

Customer is asking if Q201 FET can turn ON with 24V? Seems NO for me as higher potential is needed at Source pin prior to external supply (24V).

Question to ask:
Can you help provide a safe design for this protection?
Also, what are the values of resistors, capacitors here?

Thank you.

Regards,
Archie A.

PS: I am also checking the other device other than performing this safety via comparator: LM9061

  • 0
    Guru 140200 points

    Hi Archie,

    I don't understand how the circuit shall work. Is this an NMOS? How shall the gate source voltage be controlled? What is connected to "Ex_SUP" and what signal shall the comparator generate?

    Please write some lines and explain how the circuit shall work.

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 15779 points

    Hello Kai,

    Actually, we are trying to implement the functionality like when the external supply is ON, the battery should be made off.

    For that case, we using TLV1811 and external supply is checked with respect to ground, then the comparator output is fed to PMOS and make it turn off. As shown in the attachment X1 and X2:

    X1:

    .

    X2:

    Customer is asking assistance regarding the schematic preparation for using TLV1811- as a voltage comparator and when external supply is ON, it generates enough output to turn off the Pmos in X2 file in the attachments. Along with the reverse polarity protection of the battery.

    Thanks,
    Archie A.

  • 0 in reply to ArTzy
    TI__Genius 11701 points

    Hi Archie, 

    Sorry I missed your post, will take a look in depth tomorrow. But to clarify, it looks like you’re creating some sort of or-ing mosfet controller to switch between the external 24V supply and the battery right? What is the voltage of V_BAT?

  • 0 in reply to Chi Nguyen1
    TI__Genius 15779 points

    Hello Chi,

    Thank you.

    Yes, we are trying for OR-ing MOSFET control. The comparator we are planning to use is TLV1811 and we are planning to use the battery of 8V.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Genius 11701 points

    Thanks for the follow up. My concern would be prior to the 24V supply if there are any voltages applied to the inputs when the comparator is not powered. Whats VCC connected to the right in X1?

    I was thinking you could try using the dual channel TLV1812 to switch between the 24V supply and 8V battery using two fets similar to this circuit: ORing MOSFET controller with comparator circuit (ti.com).

  • 0 in reply to Chi Nguyen1
    TI__Genius 15779 points

    Hello Chi,

    Customer is planning to use this circuitry.

    Can you please help us with the Schematic of TLV1811 which one terminal is connected to external supply and that is compared with the ground? Then output is generated. Can you please help us with the application design of TLV1811 only?

    That would be very helpful.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Genius 11701 points

    Archie,

    How is the comparator being turned on? Is the comparator powered separately on a different supply? or through the 24V supply? I am not sure if the comparator is turned on and the voltages are applied to the inputs before it is turned on. 

  • 0 in reply to Chi Nguyen1
    TI__Genius 15779 points

    Apology Chi,

    But still unable to receive updates from customer other than their request for application design of TLV1811 with the information provided.

    Regards,
    Archie A.

  • +1 in reply to ArTzy
    TI__Genius 11701 points

    Archie,

    may need more information but the idea is to ensure the comparator is ever turned on or powered before it sees the input. also looks like the reference is gnd, might need a higher reference so it can actually toggle or have a change in state as it goes above the reference.