where I S is the saturation current or scale current of the diode (the magnitude of the current that flows for negative V D in excess of a few V T , typically 10 A). The scale current is proportional to the cross-sectional area of the diode. Continuing with the symbols: V T is the thermal voltage ( k T / q , about 26 mV at normal temperatures), and n is known as the diode ideality factor (for silicon diodes n is approximately 1 to 2).