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Original question:

ULN2003B: 【ULN2003A】Off state input voltage

ULN2003B: ULN2003B

Austin Hu49
Prodigy 70 points
Part Number: ULN2003B

I am using ULN2003B for my PWM switching circuit, as shown in attached.

A 100 Ohm resistor is serial connection to restrict the current.

Input is 3V3, 100Hz & 10K Hz PWM signal. Output is supposed to be 24V PWM.

I did two batch samples. The first one is quite normal, very good behavior of ULN2003B as in the 1st oscilloscope picture. However the 2nd batch samples behave strangely which vibrating symmetrically with respect to the 24V line, as shown in the 2nd oscilloscope picture. Can anybody advise me what I might have done wrongly.

  • 0
    TI__Genius 10855 points

    Hey Austin, 

    Thanks for reaching out on E2E!

    Can you elaborate on the input voltages? For my understanding, you're PWM-ing the 24V line on SOV1 and SOV2, but not PWM-ing the 24V on the COM pin? This could potentially be causing the ringing on the 24V. 

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 70 points
    Hi Arthur,
    I connect the COM pin to 24V supply voltage. However, today I found the mistake made by myself. I actually took different measure points using the oscilloscope so that I got different results. Still, thank you very much for reply.