often used in the push-pull output stages of the power audio amplifiers that drive most sound systems. In a fully symmetrical push-pull circuit two Darlington pairs are connected as emitter followers driving the output from the positive and negative supply: an NPN Darlington pair connected to the positive rail providing current for positive excursions of the output, and a PNP Darlington pair connected to the negative rail providing current for negative excursions. Before good quality PNP power transistors were available, the quasi-symmetrical push-pull circuit was used, in which only the two transistors connected to the positive supply rail were an NPN Darlington pair, and the pair from the negative rail were two more NPN transistors connected as common-emitter amplifiers. Safety A Darlington pair can be sensitive enough to respond to the current passed by skin contact even at safe zone voltages. Thus it can form a new input stage of a touch-sensitive switch. Amplification Darlington transistors can be used in high-current circuits such as the LM1084 voltage regulator. Other High current applications could include those involving computer control of motors or relays, where the current is amplified from a safe low level of the computer output line to the amount needed by the connected device. See also Insulated-gate bipolar transistor ULN2003A Sziklai pair, sometimes called the "complementary Darlington", a similar configuration but with transistors of opposite type (one NPN and one PNP) Integrated injection logic (I2L) References External links "Semiconductor signal translating device" (Darlington transistor) A Darlington pair motor speed control circuit ECE 327: Procedures for Output Filtering Lab – Section 4 ("Power Amplifier") discusses Darlington pairs in the design of a BJT-based class-AB current driver in detail. Multi-stage transistor amplifiers Transistor types