a resistor 440 and the second base 412 is connected to ground via a resistor 442 the shared sub collector region n epi 420 is depicted in fig5 by the connected collectors the p region 430 formed in the n epi defines a first diode 500 while the p region 432 formed in the n epi defines a second diode 502 the p region 430 forming the anode of the first diode 500 and the p region 432 forming the anode of the second diode 502 the diodes 500 502 share a common cathode as defined by the n epi and as depicted by the connection between the diodes 500 502 in fig5 when a positive esd pulse is applied to the pad 404 the upper diode 500 is forward biased thus providing a lower voltage on the collector of the upper npn bjt 510 than the emitter 400 of npn 510 the base collector junction of the lower transistor 512 is in turn reverse biased at a certain voltage the base collector junction of transistor 512 breaks down causing minority carriers in the base collector junction which allows current to flow through the upper diode 500 and the lower resistor 442 the voltage drop across the resistor 442 opens the transistor 512 the forward biased diode 500 provides additional injection of holes which leads to the increase of the current and compensates for the space charge of carriers.