TIP127PNP Darlington power transistor

TIP127 is a PNP Darlington power transistor. Two transistors share a collector, with the first emitter driving the second base for high overall current gain. Internal base-emitter resistors provide discharge paths, while the external circuit controls the operating point. The selected onsemi TIP127G uses a TO-220 body with base 1, collector 2 and emitter 3. MJD127T4G is the manufacturer’s documented DPAK replacement family: its physical layout, thermal limits, leakage and electrical test points must be checked separately. The example switches a 12 V resistor load from the positive side. A source-referenced buffered driver sinks base current to turn on and returns to the emitter voltage to turn off. The displayed currents and power are calculations using stated voltage-drop assumptions.