I understand that when you have a diode that is in forward bias, it can be modeled by a resistor and a voltage source, as seen in the top right of this diagram.

However, I'm confused about the negative bias region (modeled by the bottom left corner resistor/source combination). If the anode of a diode has positive voltage with respect to the cathode, why isn't the resistor/source combination modeled like this?

I feel like I'm missing something really fundamental here.

Thank you for your help

EDIT to include further questions requiring clarification:

(1) Using the forward bias diode model. If I use a positive voltage (1.6V) source greater than the "turn-on-voltage(0.6V)", I get a positive (clock-wise) current which is the same as the value given in the piece-wise linear diode model graph.

However, when I use a Voltage less than the 0.6V "turn-on-voltage", I get a negative current. What is this negative current telling me?

I understand that when you have a diode that is in forward bias, it can be modeled by a resistor and a voltage source, as seen in the top right of this diagram.

However, I'm confused about the negative bias region (modeled by the bottom left corner resistor/source combination). If the anode of a diode has positive voltage with respect to the cathode, why isn't the resistor/source combination modeled like this?

I feel like I'm missing something really fundamental here.

Thank you for your help

EDIT to include further questions requiring clarification:

(1) Using the forward bias diode model. If I use a positive voltage (1.6V) source greater than the "turn-on-voltage(0.6V)", I get a positive (clock-wise) current which is the same as the value given in the piece-wise linear diode model graph.

However, when I use a Voltage less than the 0.6V "turn-on-voltage", I get a negative current. What is this negative current telling me?

(2)

Also, assigning a voltage of -7.2V and using a clockwise current loop. Why do I get a value of -110mA when I should be getting -100mA according to the graph?

I understand that when you have a diode that is in forward bias, it can be modeled by a resistor and a voltage source, as seen in the top right of this diagram.

However, I'm confused about the negative bias region (modeled by the bottom left corner resistor/source combination). If the anode of a diode has positive voltage with respect to the cathode, why isn't the resistor/source combination modeled like this?

I feel like I'm missing something really fundamental here.

Thank you for your help

I understand that when you have a diode that is in forward bias, it can be modeled by a resistor and a voltage source, as seen in the top right of this diagram.

However, I'm confused about the negative bias region (modeled by the bottom left corner resistor/source combination). If the anode of a diode has positive voltage with respect to the cathode, why isn't the resistor/source combination modeled like this?

I feel like I'm missing something really fundamental here.

Thank you for your help

EDIT to include further questions requiring clarification:

(1) Using the forward bias diode model. If I use a positive voltage (1.6V) source greater than the "turn-on-voltage(0.6V)", I get a positive (clock-wise) current which is the same as the value given in the piece-wise linear diode model graph.

However, when I use a Voltage less than the 0.6V "turn-on-voltage", I get a negative current. What is this negative current telling me?