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I have a flashlight that malfuntions. I opened it up and traced the circuit, came up with this schematic enter image description here

enter image description here

Power input 3V, LED bulb dia. 9mm

I checked the transistor with a multimeter. One side has reading, the other side none. So, I know there's something wrong with it. I want to replace it with a good one. I searched the web with the number on the housing which is 0118, and found nothing. Does anyone know what kind of transistor(part #) I can use to replace that defective one?

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    \$\begingroup\$ Your diagram looks very strange. If it is correct, then a transistor has no business being where it is. I rather expect the circuit to be different, in such a way that the transistor makes sense. That, or else it isn't a transistor. \$\endgroup\$ – JRE May 23 '17 at 6:03
  • \$\begingroup\$ Might be an scr, would be strange in a flashlight, though. \$\endgroup\$ – JRE May 23 '17 at 6:11
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    \$\begingroup\$ Even more likely, if it is an LED light it might be a voltage regulator configured as a constant current source. Your diagram would still be off, though. \$\endgroup\$ – JRE May 23 '17 at 6:17
  • \$\begingroup\$ @JRE I think you must be right. ST micro has the part P0118DA and it's in the right package, too. I'll delete my answer. \$\endgroup\$ – jonk May 23 '17 at 6:29
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    \$\begingroup\$ The green through-hole component is most likely an inductor, I would guess the 3 terminal component is a complete ic \$\endgroup\$ – sstobbe May 23 '17 at 11:01
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Found it. That is indeed NOT a transistor.

It is a CL0118 LED driver. It uses an inductor to boost the voltage of a single cell high enough to drive a white LED. It will operate from cells that are very close to empty - input range of 0.8 to 1.5V.

Link to the datasheet for the closely related CL0117

Here's the example circuit from the datasheet:

enter image description here

It looks almost exactly like yours. The part you thought was a resistor is actually an inductor. They look a lot alike, but @sstobbe is right that it is an inductor. Inductors in axial packages tend to be green, unlike beige or grey for resistors.

I've posted information and links for the CL0117 because I could find good links for it, but the CL0118 should match it pretty well. You'll want to buy a replacement from someplace that can give a correct datasheet, anyway.

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    \$\begingroup\$ The main difference is that the CL0117 is designed to work with 1 cell and the CL0118 is intended to work with two cells (1.8V~3.0V input voltage for the CL0118 vs. 0.8~1.5V for the CL0117). The recommended inductor value is 47uH in either case. \$\endgroup\$ – Spehro Pefhany Jan 1 '18 at 15:45

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