TO-126

TO-126 is a type of semiconductor package for devices with three pins, such as transistors.^[1] The package is rectangular with a hole in the middle to allow for easy mounting to a board or a heat sink. On one side of the package typically a metal sheet is exposed, with the transistor die bonded to the other side of the metal sheet inside the package.^[2] This allows for an efficient heat transfer from the transistor die to an external heat sink but also implies that the metal sheet is electrically connected to the die (for a bipolar junction transistor usually the collector is connected to this metal sheet).

Front and back of a transistor in a TO-126 package.

History and origin

The JEDEC TO-126 descriptor is derived from the original full name for the package: Transistor Outline Package, Case Style 126.^[3] In the updated JEDEC outline system, the package is numbered as TO-225AA.^[2]

STMicroelectronics refers to this package style as SOT-32.^[4]

National Standards

Size comparison of BJT transistor packages, from left to right: SOT-23, TO-92, TO-126, TO-3

Standards organization	Standard	Designation for TO-126
JEDEC	JEP95[5]	TO-225AA
IEC	IEC 60191[6]	A56
DIN	DIN 41869[7]	12A3
Gosstandart	GOST 18472—88[8]	KT-27[a]
Rosstandart	GOST R 57439—2017[9]
Kombinat Mikroelektronik Erfurt	TGL 11811[6]	N
	TGL 26713/09[6]	H1B

1. Russian: КТ-27

See also

• TO-66, a metal package with similar power ratings
• TO-220, a plastic package with higher power ratings