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LM78L: lifetime question

Sam Ting
Expert 3600 points
Part Number: LM78L

Tool/software:

Team,

My customer has a question about the lifetime of the LM78L05ACMX/NOPB. The device needs to be operated in a fast ON/OFF condition (see below for details). The engineers would like to know if this behaviour causes the short lifetime or early ageing. Could you please comment on this? Thanks!

Vin = 24 V
Vo = 5 V
Load = less than 20 mA
ON/OFF = 50 Hz with 50% duty cycle.

Regards,
Sam Ting  

  • 0
    TI__Expert 5380 points

    Hi Sam,

    We have not noticed a significant decrease in lifetime from these sorts of applications, but theoretically it could. We do not have hard data for this.

    During startup, the device sees a high transient current as the output capacitor charges up and current limit hasn't kicked in. This will be the source of the impact.

    The ripple current rating of your capacitors should be the limiting factor in this sort of system.

    There may also be some reverse current.

    Does the output need to switch between ON/OFF too or is it just a result of the input rail being 50% Duty Cycle @ 50Hz?

    Is the input rail switching to 0V or High Impedance in its "OFF" state

    Best,

    Gregory Thompson