Transistor Case Packages

TO-254 Package

Transistor Packages TO254 Case style, Metal Tab

TO-254 Package
TO-254 Transistor Package

TO-254 is a through-hole device with a metal tab for a heat sink.
The metal tab may also be used to attach to a larger heat sink.

TO-254 BJT Terminals: Lead 1, Base. Lead 2, Collector. Lead 3, Emitter
TO-254 FET Terminals: Lead 1, Drain. Lead 2, Source. Lead 3, Gate
TO-254 Dual Diode Terminal: Lead 1, Anode. Lead 2, Common Cathode. Lead 3, Anode

Tab mount. A type of package which provides a method of readily attaching one surface [metal tab] of the semiconductor device to a heat sink or other heat dissipater to achieve thermal management of the case temperature. The tab may or may not be isolated from another pin [the tab may be electrically connected to another lead].

When possible the tab of the TO-254 should be bolted to a metal heat sink or chassis wall. An example clip-on heat sink is shown above, which just clips on the metal tab using compression, and requiring no tools.

When the TO-254 is bolted to a printed wiring board a large copper pad should be located beneath the metal tab to conduct heat into the PWB and away from the body of the TO-254. The copper pad or island could extend to copper plane to increase the metal and further dissipate the heat. Thermal vias may be used to conduct heat through the PWB to the opposite side of the board.
Heat conduction will be enhanced with the application of thermal grease.

If possible keep the leads of the TO-254 short so heat conduction on the terminals is dumped into the board, away from the component. Lead Length vs Heat Dissipation

Similar packages, TO-257 [slightly smaller] and TO-258.

Example Devices that use the TO-254 package include;
Which also happen to be component derating curves.
FETs: 2N6766T1 FET, and 2N6770-T1 FET
Transistors: 2N6249 BJT, and 2N6249T3 BJT

TO-254 Semiconductor Devices
NPN Power Transistors; 2N6306-T1,2N6308-T1, 2N6249-T1, 2N6250-T1, 2N6251-T1
PNP High-Power Transistor 2N7369
NPN High-Power Transistor 2N7368
High-Power NPN Darlington Transistor 2N7370
High-Power PNP Darlington Transistor 2N7371
Radiation Hardened (Total Dose and Single Event Effects) P-Channel Field Effect Transistor [FET],2N7403, 2N7404
Radiation Hardened (Total Dose and Single Event Effects) N-Channel Field Effect Transistor, 2N7405, 2N7406, 2N7407, 2N7408

TO-254AA Semiconductor Devices
PNP Power Transistor, 2N7372
NPN Power Transistor, 2N7373, 2N6676T1, 2N6678T1
PNP High-Power Darlington Transistor 2N7371
NPN Power Darlington Transistor, 2N7575, 2N7576, 2N7577

N-Channel High Voltage Field Effect Transistor, 2N7387
N-Channel Repetitive Avalanche Field Effect Transistor 2N7224, 2N7225, 2N7227, 2N7228, 2N7218, 2N7219, 2N7221, 2N7222
P-Channel Repetitive Avalanche Field Effect Transistor 2N7236, 2N7237

N-Channel Radiation Hardened Field Effect Transistor, 2N7268, 2N7269, 2N7270, 2N7394, 2N7292, 2N7294, 2N7296, 2N7298, 2N7431, 2N7432, and 2N7433
P-Channel Field Effect Transistor Radiation Hardened (Total Dose Only), 2N7424, 2N7425, 2N7426, 2N7422, 2N7423
N-Channel Radiation Hardened Field Effect Transistors, Total Dose and Single Event Effects [Enhancement-mode, MOSFET], 2N7444, 2N7434, 2N7391, 2N7392, 2N7509, 2N7510, 2N7511, 2N7470T1, 2N7471T1, 2N7478T1, 2N7475T1, 2N7476T1, and 2N7477T1
Power Rectifier Diode, Common Cathode or Anode Center Tap, 1N6828, 1N6828R, 1N6833, 1N6833R

Editor note; In some cases the internal connections of the semiconductor may be swapped. For example a 1N6828 defines a dual diode component with a common Anode [and two Cathode leads]. While a 1N6828 defines the same semiconductors, but connected as a common Cathode [and two Anode leads]. At least in the case of the 1N6828, the tab is isolated from the semiconductor. Check the specific data sheet to determine if a particular component uses the tab as an electrical connection.

Transistor Package
Flange-Mounted, Peripheral Leads

Free-standing Clip-on Metal Heat Sink with Fins
TO-254 Heatsink

TO-254 Transistor Dimensions
TO-254 Package Dimensions

BJT Package styles.
FETs and BJTs Manufacturers
Radiation Terms

TO-254 Common Cathode Connections
Dual Diode Common Cathode

PC motherboard

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Modified 6/13/15
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