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Original question:

SN6501-Q1: SN6501-Q1&SN6505-Q1 difference.

SN6505B: Output Protection

Garret Holt
Intellectual 1050 points
Part Number: SN6505B

Hello Team,

We are using SN6506B for an isolated gate drive power supply in a high voltage power supply. The secondary side of the transformer experience a large voltage swing every time the power transistor switches.  We are finding dV/dt induced transient voltages occurring at the D1 and D2 pins of the SN6505B that approach the absolute maximum rating of the part (16 V).  Are you aware of any clamping or protection techniques that can be used with the SN6505B?  We have tried Zener diodes, but they tend to cause heating problems in the SN6505B.  We are assuming this is due to the capacitance on the Zener diodes. Thanks for your feedback!


Regards,


Garret

  • 0
    TI__Genius 17100 points

    Hi Garret,

    Thank you for posting to E2E!

    Zener diodes are acceptable to protect D1/D2 switching lines from transients, but the Zener voltage spec must be >2x input Vcc  and <16V to allow enough headroom for the SN6505's push-pull action. If the Zener voltage is too low, the power supply could become unbalanced, causing the SN6505 to sink more current than necessary.

    Additional options depend on the strength and duration of the transient induced from the power transistor switching. Can you share oscilloscope waveforms of the following three points on the same screen?

    1. The isolated output voltage line
    2. D1 or D2 switching lines
    3. One of the transformer output lines (before the diodes)

    A schematic will also be helpful to identify other aspects this transient may be affecting. Please do provide a schematic if possible, and if you would like to share it privately, you may send me a Request to Connect and Personal Message.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points

    Hi Garret,

    Please do provide the information requested above if possible, otherwise Zener diodes with a Zener voltage spec >2x input Vcc  and <16V are a preferred method to protect the SN6505 D1/D2 switching lines from overvoltages, along with TVS diodes, and it's possible the Zener voltages are too low for diodes being used so far.


    Respectfully,
    Manuel Chavez