Transistor Case Packages

TO-257 Package

Transistor Packages TO257 Case style, with Metal Tab


TO-257 Transistor Package
TO-257 3-Terminal Package

The TO-257 transistor is a through-hole device, with three leads and a tab. Although not shown the leads may also be bend upwards, but a bit less common. Another variant uses semi-flexible leads with the origins being rigid which is even less common.

TO-257 BJT Terminals: Lead 1, Base. Lead 2, Collector. Lead 3, Emitter
TO-257 FET Terminals: Lead 1, Drain. Lead 2, Source. Lead 3, Gate





Tab mount. A type of package which provides a method of readily attaching one surface of the semiconductor device to a heat dissipater [heat-sink] to achieve thermal management of the case temperature. If required a metal washer and thermal grease could also be used.

Similar packages, 2-Terminal TO-257, and TO-254 [with different dimensions].

Devices that use the TO-257 package include;
2N6249T3 Transistor, and 2N6676T3 Transistor

TO-257 Transistor Types
NPN Power Transistors; 2N6306-T3, 2N6308-T3, 2N6249-T3, 2N6250-T3, 2N6251-T3
N-Channel Radiation Hardened Field Effect Transistor 2N7380, 2N7381 [TO-257AA]
P-Channel Radiation Hardened Field Effect Transistor 2N7382, 2N7383 [TO-257AA]
N-Channel Field Effect Transistor, Radiation Hardened (Total Dose and Single Event Effects), 2N7399, 2N7400, 2N7401, 2N7402, 2N7512, 2N7513, and 2N7514
P-Channel Field Effect Transistor, Radiation Hardened (Total Dose and Single Event Effects), 2N7440, and 2N7441
Diode, Silicon, Schottky, Power Rectifier, Common Cathode or Common Anode Center Tap 1N6785

TO-257AA Transistor Types
Common Cathode Gallium Arsenide Power Rectifier Diode 1N6753 [Anode (I) 1, Anode (II) 3. Cathode 2]
Gallium Arsenide Power Rectifier Diode 1N6757 [Anode 1, 3. Cathode 2]
Dual Common Cathode/Anode Center Tap Ultrafast Power Rectifier Diode, 1N6762 through 1N6765 [Anode (I) 1, Anode (II) 3. Cathode 2]
Diode, Silicon, Power Rectifier, Dual, Common Cathode or Anode Center Tap, Ultrafast, Types 1N6768 through 1N6771, 1N6772, 1N6773 [Anode (I) 1, Anode (II) 3. Cathode 2]
Field Effect Radiation Hardened (Total Dose and Single Event Effects) Transistors, N-Channel, 2N7465T3, 2N7466T3, 2N7482T3, 2N7483T3, and 2N7484T3
NPN Power Transistor 2N6676T3, 2N6678T3

Diode Array; 1N6664 through 1N6666
Terminal 1, Anode 1
Terminal 2, Cathode 1, 2
Terminal 3, Anode 2

1N6664 TO-257 Diode Array
1N6664

Editor note some use the term Tab Mount, others use Flange-Mount.
The TO-257 is part of the TO-25x series of component packages.

Transistor Package
Flange-Mounted Header Family






TO-257 Dimensions
TO-257 Transistor Package Dimensions
Transistor Pinout

Semiconductor Packages.
FETs / BJT Manufacturers
Heat Sink Manufacturers

Transistor part number are examples.
Devices could exist in other packages.




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Modified 6/13/15
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