Labeled D53 on PCB board for diode, SOT-89 package with marking "43."

It's part of a pulse-generator section on a DC power supply, it's right by an opto-coupler. This picture looks exactly like it, but I can't find any standard distributors in the U.S. I'm scared to throw something from Amazon.com on the board.

This Amazon link has a picture that looks exactly like the chip.

enter image description here

  • 4
    \$\begingroup\$ Add a photograph of the PCB and we stand a better chance. D53 is a component reference designator, so isn't going to help unless we have the component list. Do you know who the manufacturer is or anything else? \$\endgroup\$
    – Puffafish
    Sep 2, 2020 at 14:30
  • 2
    \$\begingroup\$ SMD codes are Mfg specific unless off patent (generic) \$\endgroup\$ Sep 2, 2020 at 14:32
  • \$\begingroup\$ Could it be a BAS40 of Diodes Incorporated? \$\endgroup\$
    – Raul Rosa
    Sep 2, 2020 at 15:17

1 Answer 1


Page 27 has your answer on bottom right.

I searched using D53 diode codes SOT-89. 43 is just for mfg traceability or date code last digits YM or YYWW

  • \$\begingroup\$ I teach how to search/ read, you can spoon feed regardless of the rules. -1 \$\endgroup\$ Sep 2, 2020 at 15:35
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 It's not about rules, its about creating a good answer. What happens to the answer when the link goes down? You might as well have not wasted your time. Thanks for fixing the answer \$\endgroup\$
    – Voltage Spike
    Sep 2, 2020 at 16:59

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