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LM4041C: Defective parts

Douglas Reneker
Prodigy 10 points

Part Number: LM4041C
Other Parts Discussed in Thread: TL431

LM4041 ADJ regulator in TO92 package. Wired with anode to return, 10K ohms from adj to return, 47K ohms from cathode to adj, 2K ohms from cathode to positive supply (7 - 8.5 volts), careful not to exceed 10 volts. Should regulate to about 7 volts; measured approx. 1.5 volts at cathode, about 0.4 volts at adj. Problem observed with multiple parts. Even if positive supply is insufficient, should not see such low voltages!

Pinout used:  TO-92 facing the flat surface, leads down:  adj on the left, cathode in the middle, anode on the right.

Parts are marked:
(N)07111
4041C
IZADJ
where (N) is the old National Semiconductor logo.
Parts were purchased 2 Mar 2021.

I really think these parts are defective; I got my circuit working with TL431.

  • 0
    TI__Guru 56345 points

    Hi,

    During your test setup, do you have a load on Vz.  See below.

    I have checked your numbers and your setup should work.  Vz should be around 7V.  The current (assuming no load) going into the cathode was calculated to be 1.386mA, which is below the 12mA rating.

    Just to make sure, can you provide a schematic of your setup?

    Ben

  • 0
    Prodigy 10 points

    Ben -

    Thanks for taking the time!

    Your picture is the schematic I described.  Rs is 2K, R1 47K, R2 10K, and Vs 7 - 8.5.  I've not applied a load resistance, Rl, so all the current goes through the part or the R1/R2 divider.

    The original circuit drove the gate of a power MOSFET; when I discovered it wasn't working, I wired up a part on a prototype board.  I bought 20 of these things, and haven't found a good one yet. Three more parts have failed on the prototype board since!

    As mentioned earlier, I've gotten the MOSFET circuit working with a TL431; I liked the LM4041, since it takes less current, and is less finicky about capacitive loading.

    I'd like TI to take these parts and analyze them to find out what is wrong!  They don't even act like fixed 1.2 volt LM4041 parts.

  • +1 in reply to Douglas Reneker
    TI__Guru 56345 points

    Hi,

    I think I know the problem.  Can you switch R1 and R2?  If you noticed from the schematic, VREF is across R1 and not R2.  Therefore, 1.225V is across the 47K resistor.  With what you have described, you have 10K for R1.  As shown below here is what I am calculating:

    Vz = 1.225V*(1+(10K/47K)) = 1.486V

    Switching resistor values:

    Vz = 1.225V*(1+(47K/10K)) = 6.98V

    Try switching the resistor values and let me know if you are finally getting what you are expecting.

    Ben

  • 0
    Prodigy 10 points

    Ben -

    That sorted it out!  Shame on me for not reading the data sheet carefully!

    Thanks,

    Doug R.

  • 0 in reply to Douglas Reneker
    TI__Guru 56345 points

    Hi Doug,

    I am so glad to hear that everything has been sorted out!  Glad to be of help.  Good luck!

    Ben