what is darlington arrays?

Answer 1

A darlington array is several darlington transistors housed in the same package. Each darlington will be made up of one pair of transistors.

Sometimes arrays have shared pins between devices. For example, all of the emitters of the transistors may be tied together and brought outside the package on a single pin.

See the link below for a spec sheet on one such device.

WK

Answer 2

A darlington transistor is a network of two transistors. The collectors are tied together, and the emitter of one transistor is connected to the base of the other. The combination forms a new transistor having its collector the joined collectors, the free base and free emitter forming the new base and emitter. Darlington transistors have very high forward current gain (beta), basically the product of the gains of each transistor, but also have twice the base-emitter drop of a single transistor (or 1.4v instead of .7v for silicon transistors).