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I'm trying to identify a specific component on a circuit board here (circled in red on the photo, and highlighted in red as "Q1" in the circuit). Note that the four diodes, one capacitor, and the voltage regulator are all lumped together as "DC 5v" in the circuit diagram, while the three 470 ohm resistors on the right are lumped together as R3:

PCB photograph

Circuit diagram

For context, I should probably describe the function of the circuit. When voltage is first applied to the circuit, LED D1 is lit. However, when S1 is closed momentarily, D1 is turned off and stays off until S1 is pressed again (at which point it turns on, rinse and repeat).

Obviously, without any identifying markings, it's impossible to identify the component Q1 is exactly, but I just need some initial direction so that I can choose a component of similar function and value.

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    \$\begingroup\$ A flip-flop ic might make sense here. \$\endgroup\$
    – evildemonic
    Dec 8, 2022 at 17:53
  • \$\begingroup\$ It's switching power, it's an IC, and it's an SOT-5 package, so there are some search terms to start with. Not sure if I should post an answer as this question may be bordering on being off topic. \$\endgroup\$
    – GodJihyo
    Dec 8, 2022 at 17:53
  • \$\begingroup\$ @evildemonic It's almost certainly a dedicated power switch IC,. \$\endgroup\$
    – GodJihyo
    Dec 8, 2022 at 17:54
  • \$\begingroup\$ @winny Why would a switch need an inductor? \$\endgroup\$
    – GodJihyo
    Dec 8, 2022 at 17:56
  • \$\begingroup\$ Sorry, I read switcher, as in DC-DC. \$\endgroup\$
    – winny
    Dec 8, 2022 at 18:04

2 Answers 2

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It appears the P/N is rubbed off by Mfg, so I am wondering why you need this info. Pls Advise.

The momentary switch triggers a toggle function, normally done by Qbar to D and clk input pulse.

I found an SOT-23 with such a device but it is not compatible and needs a jumper from Qbar to and pullup R on CLK. So keep looking or ask a better question.

enter image description here

Then I looked closer to see your unreadable photo to see a SOT23-6 not the -5 in your schematic.

The correct pin#'s are CCW from pin 1 not alternating sides for these chips.

But this still does not match since the power is on the center pins. So keep looking.

enter image description here

REV A

Your questions needs more clarity/accuracy to find a match to verify Vcc and Gnd pins. Yet the answer given by @Tarabas seems close but not quite the same.

enter image description here

Neither does a single D FF IC below fit exactly , but can be made to work with Qbar to D input jumper and CLK in. (CLR# to V+)

enter image description here

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    \$\begingroup\$ It's definitley SOT23-5. There is no physical pin at the "right middle" position, nor is there a solder pad. \$\endgroup\$
    – Trainboy
    Dec 9, 2022 at 17:04
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    \$\begingroup\$ There is also no physical connection between the "left middle" lead and anything else on the board. It's just an open lead. Trust me, I spent more than half an hour trying to figure that out. \$\endgroup\$
    – Trainboy
    Dec 9, 2022 at 17:10
  • \$\begingroup\$ As for the pin numbers, I just used what Visio assigned in my quick and dirty drawing, which was only meant to illustrate the component in question. As for the photo being unreadable, what do you mean? \$\endgroup\$
    – Trainboy
    Dec 9, 2022 at 17:17
  • \$\begingroup\$ If you see a physical lead then show it on logic schematic with no connection. The photo says it has 6 leads which is important info to match part, but is unreadable for surface reflection of numbers which is also important info. The convention for pin numbers, now you know, is left to right and CCW top view from dot for pin 1. Connectors may have different rules than IC's. \$\endgroup\$
    – Tony Stewart EE75
    Dec 9, 2022 at 18:27
  • \$\begingroup\$ Alright. I thought I was as clear as I could possibly be in the logic schematic. So I'll try to be clearer here. Counterclockwise from top left pin: - Pin 1 (a1 on my schematic): 5V supply (you can call this Vcc if you want) Pin 2 (a2 on my schematic): No connection Pin 3 (a3 on my schematic): Ground Pin 4 (b3 on my schematic): This lead shorts to ground when the circuit is to be turned off Pin 6 (b1 on my schematic): "input" lead. \$\endgroup\$
    – Trainboy
    Dec 10, 2022 at 16:43
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This could well be a On/Off controller with debounce, something like to MAX16054 for instance, but with just one of the outputs. I'll assume it has an inverted output that is pulled down after the first button press, and lowers the base voltage enough to switch off the transistor.

See the datasheet for inspiration: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX16054.pdf

It would help a bit to have the size of the package, to know if it is of size SOT23-5 or SC70-5. It might not be relevant here, but would improve your question to have the resistor values in your reverse engineering schematic ;-)

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  • \$\begingroup\$ SOT23-5 R1 is 4.7k, while R2 is 220 ohms. R3 is not relevant. \$\endgroup\$
    – Trainboy
    Dec 10, 2022 at 16:49

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