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

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.

PC motherboard

Distributor rolodex Electronic Components Electronic Equipment EDA CDROM Software Engineering Standards, BOB card Cabled Computer Bus Electronic Engineering Design Table Conversion DB9-to-DB25.
DistributorsComponents Equipment Software Standards Buses Design Reference
Modified 6/13/15
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