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I got 2 samples of LP2905CZ (TO-92) voltage regulator. First sample is made by TI and second on by On Semiconductor. Links of the datasheets:

On Semiconductor

TI

Due to ignorance, I just read the datasheet of On Semiconductor and started to test the two regulators but later discovered that the TI one does not work. After trying to check all breadboard connections, I thought to check the data sheet of TI one which revealed some interesting finding.

For the On Semiconductor:

PIN 1: Output  PIN 3 = INPUT

For TI:

PIN 1: Input PIN 3 = INPUT

I understand that I should have checked the datasheet before hooking these, but my question is why do the manufacturers don't follow a logic layout (e.g. PIN 1 = INPUT and 3 = OUTPUT like all(!) LM7805)

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  • \$\begingroup\$ A standardized layout might cause problems if the wrong part was accidentally installed in a circuit. 7805 and 7905 have different layouts as a rudimentary safety system. \$\endgroup\$
    – StainlessSteelRat
    Commented Apr 17, 2015 at 13:15
  • \$\begingroup\$ Whats clever about the 78 and 79 series of regulators is that pin 1 on both is always the most positive voltage and pin 2 on both the most negative voltage hence they are hard to destroy when swapped. \$\endgroup\$
    – Andy aka
    Commented Apr 17, 2015 at 14:04

1 Answer 1

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I see no difference in the pin outs at all: -

enter image description here

TI's offering in red box; ONsemi to the right and lower

Why do the manufacturers don't follow a logic layout (e.g. PIN 1 = INPUT and 3 = OUTPUT like all(!) LM7805)

Generally they don't and, unless I'm being really stupid they don't for the LP2950.

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    \$\begingroup\$ Yes you are right. My mistake in interpreting the bottom view as top view. Thanks!! \$\endgroup\$
    – Anuj Purohit
    Commented Apr 17, 2015 at 9:34

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