Can Kirchoff's laws and Ohm's law be used on circuits with diodes?

[SiennaB]

Homework Statement

Can Kirchhoff's voltage and current laws, and Ohm's law, be used when analysing circuits with constant voltage and current sources, but also diodes?

I'm trying to analyse such a circuit, and I'm finding that current is flowing backwards through one of the diodes.

Homework Equations

Kirchhoff's Voltage Law: sum of voltage drops in a closed loop is zero.
Kirchhoff's Current Law: sum of currents entering a node equals sum of currents leaving a node.
Ohm's Law: V=IR

The Attempt at a Solution

 

[darkxponent]

Kirchhoff's Laws that is the current law(KCL) and the Voltage law(KVL) is indeed valid everywhere, whether the circuit contains diodes, transistors or any other nonlinear element.

The thing which is not valid with the nonlinear elements in circuit is the principal of superposition.

Regarding your question on Ohm's Law, ohm's law is not basically a law. when we say V=IR, means the resistance of the element is constant. For nonlinear elements resistance in not usually important, as V is not linear to I. We still define resistance of nonlinear elements using R-= V/I or R = dV/dI.

 

[SiennaB]

Great, thanks for your reply.

 

[darkxponent]

you are welcome!

 

[rezeew]

Yes, Kirchhoff's laws and Ohm's law can be used when analyzing circuits with diodes. However, they may need to be modified to account for the behavior of diodes.

In the case of Kirchhoff's voltage law, the sum of voltage drops in a closed loop will still be zero, but the voltage drop across a diode will depend on the direction of current flow. If the diode is forward biased, it will have a small voltage drop (typically around 0.7V), and if it is reverse biased, it will have a large voltage drop (close to the supply voltage). Therefore, when applying Kirchhoff's voltage law, you must take into account the direction of current flow through the diode and the corresponding voltage drop.

Similarly, Kirchhoff's current law still applies, but the current through a diode will be dependent on its bias. In a forward biased diode, current will flow through it as normal, but in a reverse biased diode, very little current will flow. Therefore, when applying Kirchhoff's current law, you must consider the direction of current flow through the diode and the corresponding current value.

Ohm's law can also be used in circuits with diodes, but again, it may need to be modified to account for the behavior of diodes. Ohm's law states that the voltage across a resistor is equal to the current through it multiplied by its resistance (V=IR). In the case of a diode, the voltage-current relationship is not linear, so Ohm's law cannot be directly applied. However, you can still use the concept of voltage and current to analyze the behavior of a diode in a circuit.

In summary, Kirchhoff's laws and Ohm's law can be used in circuits with diodes, but they may need to be modified to account for the behavior of diodes. It is important to consider the direction of current flow and the voltage-current relationship of the diode when applying these laws.