Transistor Case Packages

TO-72 Package

Transistor Can Packages TO-72 Case style, Metal Can

TO-72 Metal Package
TO-72 Metal Can

TO-72 Metal Package

This drawing shows the basic outline of the TO-72 package. The call-outs correspond to the dimensions used in the table in the lower right corner.

Four pins [4-terminals] are shown in this diagram, but three pins would be much more common. In fact most of these packages may have, or could have, more than three pins as long as the pins stay on the radius depicted.
Part of the package definition includes the pins being on a .100 pin circle.

The letter call-outs used in the drawing are the same call-outs used for any other metal can with this basic shape. However different manufacturer, or different data sheets, might use different call-outs.

The TO-72 package is a 3 pin or 4 pin device in a metal can.
A four terminal through-hole [thru-hole] device is shown above. Pin 4 may be missing.
As with any package, any number of uses will be found for a TO-72 metal can, as in a photodiode with phototransistor, or a Dual-Gate FET. Of course the pin functions change depending on what circuit resides within the device.

Like any other metal case, a number of heat sinks are possible for a TO-72 package. Normally the same heat sink will also fit a TO-18, or a TO-78 package. Many of the pages covering transistor packages also show a particular style of heat sink. There are a number of different clip-on or press-on heat sinks that work for a round metal can. A small-fin press-on heat sink is shown above. Normally produced in Black Anodized Aluminum.
Check the thermal Resistance of the heat sink and use thermal grease if required.

The 2N4416A N-Channel FET uses the TO-72 package as;
Lead 1 = source, lead 2 = drain, lead 3 = gate, lead 4 = case.

The 2N3821 N-Channel Depletion Mode FET [also 2N3822, 2N3823 FETs];
Lead 1 = source, lead 2 = drain, lead 3 = gate, lead 4 = case.

The 2N2857 Low-Power NPN Transistor uses the TO-72 package as;
Lead 1 = emitter, lead 2 = base, lead 3 = collector, lead 4 = case (electrically connected) PNP Switching Transistor 2N4261.

The active elements [terminals] are electrically insulated from the case
Terminals 1, 2, and 3 are insulated from the case.

A similar size metal-can is the TO-71 package with 6 leads.

Package Style:
.100 Pin Circle, 4 Axial Leads
4-Terminal Metal Can

Slide-on Metal Round Heat Sink
TO-72 Heatsink

TO-72 Package Dimensions
TO-72 Mechanical Dimensions

Related Technical Pages;
Types of Transistor cases.
Guideline to Derating Transistor.
Definition of Transistor Terms.
Manufacturers of FETs and BJTs

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Modified 6/13/15
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