Transistor Package TO247 Plastic Encapsulated Case, Metal Plate
TO-247AC Transistor Package Out-line and Dimensions
TO-247AC is a three-lead through-hole device with a metal plate for a heat sink.
The generic TO-247 part may have more than 3 leads, this page only deals with the TO-247AC part. Terminal 4 [metal tab] is connected to the Drain and should also be used to attach to a larger heat sink.
TO-247 BJT Terminals: Lead 1, Base. Lead 2, Collector. Lead 3, Emitter
TO-247 FET Terminals: Lead 1, Gate. Lead 2, Drain. Lead 3, Source. Lead 4, Drain
TO-247 SCR Terminals: Lead 1, Cathode. Lead 2, Anode. Lead 3, Gate.
When not used as an electrical connection, Lead 4 is a thermal tab.
Tab mount. A type of package which provides a method of readily attaching one surface of the semiconductor device to a heat sink to achieve thermal management of the case temperature. In this case the 'Tab' is an exposed metal die on the under-side of the component.
When possible the body of the TO-247 should be bolted to a metal heat sink or chassis wall using thermal grease or conductive epoxy. When the TO-247 is bolted to a printed wiring board a large copper pad should be located beneath the exposed die to conduct heat into the PWB and away from the body of the TO-247. 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.
If possible keep the leads of the TO-247 short so heat conduction on the terminals is passed into the board, away from the component. In other words mount the case or body of the device near the surface of the board.
Indicated in a data sheet: The TO-247AC package is preferred for commercial-industrial applications where higher power levels preclude the use of TO-220AB devices. The TO-247AC is similar but superior to the earlier TO-218 package because of its isolated mounting hole.
Encapsulated Plastic, N-Channel Field Effect Transistor, 2N7563, 2N754, 2N7565
Editor note: As with many packages; the TO-247AC shown is one member of a series of parts in the TO-247 family. The physical body of the device may change as more pins are used in this body style [only a three pin style is shown]. The 2 pin TO-247 version will have the same physical dimensions as the 3 pin TO-247, while a 4 pin will have different dimensions. That is any TO-247 with more than 2 or 3 terminals will use a larger package.