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TPS92512HV: EVM schematic

chentsu chung
Mastermind 6180 points
Part Number: TPS92512HV
Other Parts Discussed in Thread: TPS92512EVM-001

Hi,

There is a diode D1 in the user guide of TPS92512EVM-001:

1. What is the diode use for?

2. What if remove this diode from circuit?

Thank you.

  • 0
    TI__Mastermind 28655 points
    Hello chentsu,

    Diode D1 is to prevent the inductor voltage from going a diode drop above Vin if the LED stack opens. If the LED string never opens D1 isn't necessary. It may be needed during safety testing depending on how the circuit is used.

    Regards,
  • 0 in reply to Irwin Nederbragt
    Mastermind 6180 points
    Hi Irwin,

    Sorry I don't get it. For buck converter, the output voltage will be equal to Vin if duty up to 100% when LED circuit opened, am I right?
    So why it needs to be protected? Could you please explane it more detail?

    Thank you very much.
  • 0 in reply to chentsu chung
    TI__Mastermind 28655 points

    Hello chentsu,

    If the buck converter is running and you disconnect the LED string the buck inductor has current flowing.  Where does that current flow?  If there is an output capacitor it will dump its energy into the capacitor.  If the capacitor is small or there is no capacitor the voltage will rise on the open end of the inductor until it finds a path to conduct.  To figure out how high the voltage will go you use (1/2)L*I^2 compared to (1/2)C*V^2.  The capacitor portion of the equation has to go from running V to final V so (1/2)L*i^2 = (1/2)C(V2^2-V1^2) where V1 is the operating output voltage and V2 is the final voltage after the inductor discharges.

    With D1 in place the energy, once it reaches Vin plus a diode drop) will go to Vin preventing the open inductor from arcing, causing damage, or creating a safety concern.

    Regards,

  • 0 in reply to Irwin Nederbragt
    Mastermind 6180 points
    Hi Irwin,

    Understood, it's very clear, appreciate for you explain!!