Want to squeeze a bit more current through those inexpensive TO-92 package transistors? Then add a small metal heatsink.
I made this for a PWM DC motor driver, as some 2N2222 bi-polar transistors were handy. It worked OK, but the 2N2222 was getting very hot (too hot to touch.)
This will work with any TO-92 device--but the device must have a flat part to contact the sink (as TO-92 cases do.)
It's not entirely crazy; commercial heatsinks are available for this package. And the 2N2222 specs include two power dissipation ratings, Tamb <= 25 C (500-800mW) and Tcase <= 25 C (1.2-1.8 mW) (being ambient air temperature and case temperature.) Keep the case at 25 C or below, and the current rating more than doubles.
Step 1: You'll need...
-- Heatsink material: copper, aluminum or other sheet metal
-- Heat shrink tubing
-- Thermal paste compound (for CPU heatsinks)
-- A nibbler (or tin snips)
-- Files and sandpaper
Step 2: Cut out the Heatsink
The heatsink should be large enough to soak up excess heat, but can be almost any shape. However, it must have a "tab," slightly wider and taller than the transistor.
It can contain a hole for attaching to a circuit board, if that's desired.
Step 3: Fine-tune the Shape
This prevents the "tab" from sliding out of the heat shrink tubing, and off the transistor.
Note: to be honest, tapering the "throat" at the top of the tab seems to work better....the drawing illustrates this alternate method (which I used on the prototype.)