TO-46 Package
Transistor Can Packages; TO46 Case style, Metal Can
TO-46 Metal Can
TO-46 is a through-hole device with a metal lid.
Terminal identification; Pin 1 Emitter, Pin 2 Base, Pin 3 Collector.
Lead 3, the collector is electrically connected to the case.
Note the location of the identification tab to the pins.
TO-46 Dimensions
TO-46 Metal Can Outline and Package Dimensions
Fabrication hint; heat conduction occurs through the leads of the TO-46 package, so the shorter the leads of the device the better the heat conduction. The shorter the leads the lower the thermal resistance between the case of the TO-46 and the Printed Wiring Board [PWB]. Just leave an air gap between the PWB and the body of the TO-46 so there air flow is still possible under the component body.
NPN Switching Transistors use this package type including; 2N3485A, 2N3486A, 2N3737, 2N5581 and 2N5582.
SCR components found in this package style include; 2N1771A, 2N1772A, 2N1774A, 2N1776A, 2N1777A, 2N1778A, and 2N2619A.
LEDs with a glass domed metal lens can use this package; [3-leaded TO-46 header].
CLE390: 1; IRED cathode. 2; Common. 3; Photodiode Anode.
Precision Temperature Sensor: LM135, LM235, and LM335.
Pin 1, Cathode. Pin 2, Anode. Pin 3, Adjustment.
Note the LM335 may also be purchased in a 8-pin SOIC, a TO-92 or a TO-46 metal can.
However this topic only refers to the TO-46 metal can.
4 Terminal TO-46 Package.
It would seem that JEDEC shows a TO-46 package as a three leaded component, and not a four leaded component shown to the left. In general JEDEC defines this style of round package as the circular distance between the pins [0.10 in this case], without defining the number of pins. The dimension used in the graphic is termed BSC, which means Basic Spacing between Centers. Than, Basic Spacing also refers to the fact that the spacing may be changed, for example to allow insertion into a hole pattern on a printed wiring board.
However; it stands to reason that a manufacturer could use a TO-46 package, but omit one of the terminals. So a two terminal device is possible using the same dimensions as shown, but with one pin missing. Also that a four terminal package is possible as long as the pin to pin spacing is kept at 0.10 inches.
In any event, some data sheets use what is called a TO-46 case using 4 terminals as shown in the diagram. The particular package shown uses a TO-46 metal-can placed within a thermal shield, although the drawing does not show the internal shape of the metal can. Because the TO-46 is encased within a shield, the diameter and the component height has increased. A number of devices use the 4 terminal TO-46 including the following parts:
Precision Voltage Reference: LM199, LM299, and LM399.
Pin 1, Cathode. Pin 2, Anode. Pin 3, Plus Heater. Pin 4, Negative Heater.
The heater, or temperature stabilizer circuit, happens to be constructed on a single monolithic chip along with the active reference zener [used as the voltage reference].
Use the transistor package links to view other heat sink styles, many of which will also fit a TO-46 package.
