Transistor array

That is, the transistors in the array are not connected to each other to implement a specific function.

There are three main motivations for combining several transistors on one chip and in one package:[1] The matching parameters and thermal drift are crucial for various analogue circuits such as differential amplifiers, current mirrors, and log amplifiers.

Often the transistors here are Darlington pairs with a common emitter and flyback diodes, e.g. ULN2003A.

While this stretches the above definition of a transistor array somewhat, the term is still commonly applied.

For instance, for an array of NPN transistors, the substrate must be connected to the most negative voltage in the circuit.

Transistor array B342D ( HFO ) – 4 NPN transistors (here in a cassette tape recorder).
Transistor array ULN2803APG ( Toshiba ) – 8 Darlington pairs.
Transistor array chip containing two bipolar transistors.