Yup, the 4.4V is reversed biased. In most cases the, the voltage drop across the resistor would be constant becuase of a constant current in the circuit. Temperature would have some effects, but usually very little.Oh I see, so the diode with 4.4V voltage drop is reverse biased then...? shame on me for not noticing that... And btw, when using the constant-voltage-drop model for a diode, does it also mean that the voltage drop across the resistor is also constant since it is connected with the diode in a series..? and to your question - i think i dont know what limits the reverse bias voltage across a diode.