HH004F is a low power integrated boost converter IC in a TO-92 package, look exactly like a small transistor.
Though it's quite a uncommon and undocumented IC, but you may find it occasionally in some LED torches. The IC is available in many different numbering and marking.
I got one of them, and decided to draw the schematic and build a prototype.
HH004F based LED driver
This IC is typically used as a low power LED driver with 1.5V input voltage, here's the schematic.
So, it's pretty simple, just the HH004F IC, a 3.3uH inductor, a LED, a switch and a 1.5V battery.
Here's the pin out of the IC.
I decided to build a quick prototype after salvaging the IC from a torch, below the picture of my prototype.
The value of inductor is not so important, anything between 2.2uH to 10uH should work.
So, that's all for this short post. Don't forget to share your thought through the comments.
Dear Arnab
The good news is that the HH004F is easily available in ebay and other sites for about Rs 165 ($2.5). here is the link:
http://www.ebay.com/itm/50PCS-HH004F-TO92-DC-step-up-chips-Transistor-NEW-good-quality/351791436058?_trksid=p2047675.c100623.m-1&_trkparms=aid%3D2220072%26algo%3DSIC.MBE%26ao%3D2%26asc%3D42799%26meid%3D333a7ade17c84935b60a4baefa6ff35c%26pid%3D100623%26rk%3D1%26rkt%3D2%26sd%3D182219874731
Forgot to mention that the price mentioned in my previous post is for 50 pcs of the IC.
Then it's dirt cheap, I'll order some in future.
Arnab, thanks for posting! I found this "transistor" (marked HH004F) in a 3-LED stick-on closet light (2 AA batteries).
I couldn't for the life of me figure out how this "transistor" and "resistor" were doing anything. It never occurred to me it was an IC and an inductor (0 ohms, thought it was shorted).
Thanks for the feedback.