• State Resolved
  • Locked Locked
  • Replies 12 replies
  • Subscribers 32 subscribers
  • Views 2075 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ULN2803A / About Vce(sat) when the Input port pulled-up by 3.3kohm.

ACGUY
Guru 11170 points

Hi all,

Our customers are considering a change from competitors products to ULN2803A.

They have question.
When the input port pulled-up to 3.3V by 3.3kohm resistor,
How much the Vce(sat) at Ic=50mA, 80mA and 100mA?

Regards,
Nagai

  • 0
    TI__Mastermind 24485 points
    Hello Nagai-san,

    3.3kOhm is quite a bit of additional resistance at the base of the transistor.
    This would effectively act as though the input voltage was directly tied at 2.63V, which is slightly low.
    For low current applications, less than 200mA, this should be ok, but for higher current applications >250mA, this would not be recommended (it would be recommended to put a smaller additional base resistance.

    I can look further into the variance for this device, but is there a reason that they are using 3.3kohm, and would they consider decreasing this resistance?

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Guru 11170 points
    Hello Michael-san,

    They use the competitor device for electromagnetic relay turn-on.
    In the currently product circuit of their, the input port is pulled-up to 3.3V by 3.3k ohm.
    They want an information for propriety about change the device to ULN2803A.

    >> would they consider decreasing this resistance?
    If 3.3k ohm is quite a bit, they will reconsideration about it.
    I'll confirm to their that why pull-up resistor is 3.3k ohm.

    Regards,
    Nagai
  • 0 in reply to Michael J Schultis
    Guru 11170 points
    Hello Michael-san,

    Sorry, I had mistake.
    It's not 3.3k ohm, it's 1k ohm.

    Regards,
    Nagai
  • 0 in reply to ACGUY
    TI__Mastermind 24485 points
    Hello Nagai-san,

    Thank you for your confirmation.
    I will work to gather bench data to show the variance in the Vce when using a 1kohm additional base resistance. I will respond with results by end of tomorrow.

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Guru 11170 points
    Hi Michael-san,

    I have additional question.
    Our customer wants to know about internal clamp diode of the device.
    Could you provide the information about electrical characteristics of that to us?
    - When If=500mA, is there a limit to the current pulse width of this device?
    - When If=350mA, can this diode flow the continuous current?
    - How much the maximum reverse-recovery-time (Trr)?

    Best regards,
    Nagai
  • 0 in reply to Michael J Schultis
    Guru 11170 points
    Hi Michael-san,

    This is just a friendly reminder that I’m waiting for your reply.

    Thank you!
    Nagai
  • 0 in reply to ACGUY
    TI__Mastermind 24485 points
    Hello Nagai-san,

    Thank you for the reminder.
    The data points are almost the same, the 1k resistor does not make too much difference.
    Please see data below (and please note that this is typical data only and is not a guarantee of the specification):

    With no additional resistance
    50mA: 796mV
    80mA: 846mV
    100mA: 876mV
    500mA: 1450mV

    With 1k additional resistance
    50mA: 798mV
    80mA: 843mV
    100mA: 873mV
    500mA: 1436mV

    There should not be any problem using the device at these currents with the additional base resistor.

    As for you other questions regarding the flyback diode. I will have to consult with my design team, which may take some time to be able to get an answer.

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Guru 11170 points
    Hi Michael-san,

    Than kyou very much!
    I am looking forward to answers to additional questions from you.

    Regards,
    Nagai
  • 0 in reply to ACGUY
    Guru 11170 points
    Hi Michael-san,

    Do you have any update on about Trr of internal clamp diode?
    I am looking forward to reply from you.

    Regards,
    Nagai
  • 0 in reply to ACGUY
    TI__Mastermind 24485 points
    Hello Nagai-san,

    We are still working on this.

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    TI__Mastermind 24485 points

    Hello Nagai-san,

    Here is what I can answer:

    - When If=500mA, is there a limit to the current pulse width of this device?

    At 25C, the device can manage 500mA continuous current through the diode.

    - When If=350mA, can this diode flow the continuous current?

    Yes, at 25C, this current can flow continuously 

    - How much the maximum reverse-recovery-time (Trr)?

    I was able to measure the reverse recovery time of the diode on the bench. The recovery time will depend on the current flow in the ON state as well as the voltage applied to reverse bias.

    I found that with 250mA forward current and -0.4V reverse bias, the reverse recovery time is around 250ns. Note this was taken for a single unit at room temperature and is not a guarantee of the device specification.

    Best,
    Michael

  • 0 in reply to Michael J Schultis
    Guru 11170 points
    Great!!!
    Thank you very much!!!!!