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ULQ2003A-Q1: About forward voltage of diode

Junya Kato
Expert 1635 points
Part Number: ULQ2003A-Q1

Hello Team,

Please tell me the forward voltage of the diode circled below.

Best regards,
Kato

  • 0
    TI__Genius 15710 points

    Hi Kato,

    This is the parameter V_F (clamp forward voltage) in the datasheet. For this device, it is 1.7V (typ) and 2.1V (max).

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Expert 1635 points

    Hello Alek-san,

    Does the spec you answered point to the clamp diode surrounded by the red circle below?  Looking at the test circuit looks like that.
    The information I want is the Vf value of the diode surrounded by the blue circle below. Does that mean it use the same diode?

    Best regards,
    Kato

  • 0 in reply to Aleksandras_Kaknevicius
    Expert 1635 points
    Hello Alek-san,

    It is an additional question.
    If truly VF is Typ 1.7V, why is the voltage higher than VF(about 0.7V) of general diode?
    For example, although it can not be confirmed in the block diagram, are three connected in series?

    Best regards,
    Kato
  • 0 in reply to Junya Kato
    TI__Genius 15710 points

    Hi Kato,

    You are right, and thank you for catching this. VF is referring to the flyback diode, not the output clamping diode. While 0.7V is a very ideal voltage for a diode, many different types of diodes can be created, and these will result in different voltage drops. As you mentioned, it would be possible to also string diodes in series to increase the forward voltage.

    As for the forward voltage of the output clamping diode, we did not take this data when characterizing the device. With the emitter (pin E) pulled to ground, the diode should not be forward biased since the output would have to be very negative. Could you help me understand why this information is needed?

    Thanks,

    Alek Kaknevicius