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Original question:

ULN2003A: Recommendation for protection circuit

ULN2003A: required Protection circuit

Amena Mulla
Prodigy 30 points
Part Number: ULN2003A

Hello,

We are using ULN2003A to driving relay for touch electrical switches. We got many issues while in production testing as well as site issue after some time. Most common issues in ULN 7th , 6th pin output get shorted with either COM pin or GND pin of ULN. as mentioned in datasheet each channel can drive upto 500mA still it got damage. Single relay required only 37.5mA current. ULN input given by MCU which is work on 5VDC. Relay are 12VDC. 

Kindly suggest us some protection to minize this isse.

Also what if we use TBD62003AFWG? What is main difference between this? Which is better to use?

  • 0
    TI__Mastermind 32650 points

    Hi Amena,

    The peak current through a single channel is 500mA. But when more channels are being and when the duty cycle is 100%, the maximum collector current is limited.

    Please refer to Figure 4 and Figure 5 on the datasheet for further information. 

    As a further question, are you pulling the COM pin to 12V to minimize inductive kickback effects from the relay load? 

    The TBD62003AFWG look like a pin to pin compliant device.

  • 0 in reply to Shreyas Dmello
    Prodigy 30 points

    Hi shreyash,

    Yes I am pulling com pin to relay input 12V.

    Also is it necessary to add capacitor between COM and GND pin of ULN.? If yes then how to calculate its value.? What is the use of this capacitor.? What if we are not using that capacitor.?

  • 0 in reply to Amena Mulla
    TI__Mastermind 32650 points

    Amena,

    What is your logic on using a capacitor between COM and GND? I have not seen that implementation before.

    Unfortunately, with the information that you provided it is hard to troubleshoot. Can you estimate how much current is flowing through each channel? 

    These are legacy TI devices so protection features on them are limited. 

  • 0 in reply to Shreyas Dmello
    Prodigy 30 points

    Hi shreyash,

    Capacitor is used for filter purpose only. And it is also shown in datasheet Cout of 15pF. Can you explain how they calculate this value.?

    Each channel having Maximum 75mA current at 100% duty cycle.

    Now my main question is when we got damage ULN , I measure COM and output channel resistance of few channels are not match with respect to other channel.

    Is there any protection circuit we can add to minimize this issue.??

  • 0 in reply to Amena Mulla
    TI__Mastermind 32650 points

    Hi Amena,

    Are you referring to the CL=15pF in figure 18? Apologies but could you please point this out to me as I am not sure what capacitance you are referring to?

    Also, what package of the device are you using? 

    As far as protection circuitry goes, it is possible to use an external flyback diode in place of the integrated diode to increase inductive kickback protection. I have seen implementations that place a protection diode across all loads too. But this is all moot if you are electrically overstressing the part with high currents. 

  • 0 in reply to Shreyas Dmello
    TI__Mastermind 32650 points

    Hi Amena,

    I want to follow up on this thread? Have you been able to work around your issue?

    I am going to close this thread but feel free to rely and we will resume support.