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LM7481-Q1: Active rectification of 28VDC superimposed 4V pk to pk sinewave at 15khz, with 120V surge withstandability.

Sabi varghese
Prodigy 70 points
Part Number: LM7481-Q1
Other Parts Discussed in Thread: LM7481

Hello,

I am trying to understand that if i can use LM7481-Q1 for below application.

Vin: 28Vdc with 4V pk to pk 15kHz sine wave ripple, Also have a spike voltage of 120V for 1ms

Output: 28V/12A, with active rectification of 15kHz ripple

Protection: Load dump feature not required, only reverse polarity required (upto -30V continuous, and -60V peak for 1ms), so only one Mosfet will be used. Shall be able to withstand surge of 120V for 1ms & 80V for 100ms (when input voltage is above 50V Mosfet gate is not required to be driven, let the body diode conduct). Since the LM7481 is rated only upto 65V, could we use any clamp circuit with series resistor (may in ground path) to withstand the surge voltages. Plz suggest how to make LM7481 to be compatible for this surge voltage requirement application

  • 0
    TI__Guru 57737 points

    Hi Sabi,

    Thanks for reaching out to us.

    Yes, LM7480x-Q1 and LM7481-Q1 can rectify AC super imposed ripple of 4V pk-pk and 15kHz. Below are the test results with LM7480x-Q1.

    AC Super Imposed Test: 4V Peak-Peak 20kHz

    AC Super Imposed Test: 4V Peak-Peak 30kHz

    You can refer to 'Ideal Diode Controllers for Active Rectification of AC Voltage Ripple' app note for more understanding 

    LM7480x-Q1 and LM7481-Q1 can be used in common source topology to withstand 120V surge at the input. You can see a design example in datasheet which can withstand 200V unsuppressed load dump at the input. Please refer to section '10.3.1 Design Requirements for 200-V Unsuppressed Load Dump Protection' of LM7480x-Q1 datasheet. 

    The HFET is turned OFF during the surge event and the blocks the input over voltage from being seen at output as shown below. 

     

  • 0 in reply to Praveen GD
    Prodigy 70 points

    Thank you for the quick response. We had seen those load dump options.  Due to various other reasons we would need only reverse polarity and active rectification feature and can use only one Mosfet in the circuit. 

    Reverse polarity required (upto -30V continuous, and -60V peak for 1ms). Shall be able to withstand surge of 120V for 1ms & 80V for 100ms (when input voltage is above 50V Mosfet gate is not required to be driven, let the body diode conduct). Since the LM7481 is rated only upto 65V, could we use any clamp circuit with parallel zener diode for LM7481 and series resistor (may in ground path) to limit the surge voltages across LM7481. Plz suggest suitable schematic for LM7481 to be compatible for this surge voltage requirement application

  • 0 in reply to Sabi varghese
    TI__Guru 57737 points

    Hi Sabi,

    In case you do not want to use the HFET, the only option is to make sure the device does not encounter voltages beyond its Abs Max rating. 

    TVS diodes are generally used to clamp transient over voltages but the duration of the over voltage you need to clamp in this case is 100ms which is huge. I am aware of TVS devices which are rated for 10/1000 us but not for 100ms duration. As you mentioned, you can review other options like Zener + Resistance in series which can clamp the voltage at input to less than the Abs Max Rating of the device. .