You can calculate the current through the diode when it is connected in the series to the resistor using **Kirchhoff’s Voltage Law (KVL)** and the **Shockley diode equation**. This article describes the step-by-step procedure and formula to find the current through the diode.

### 1. **Kirchhoff’s Voltage Law (KVL)**:

According to KVL, in a closed electrical circuit, the sum of the voltage drop across electrical devices equals the sum of the supply voltage. The devices used in the circuit are a resistor and diode, therefore the sum of the voltage across the resistor and diode equals the supply voltage. In other words, input supply voltage V_{in} equls to the sum of the voltage drop across resistor V_{R} and diode V_{D}. For example, if the voltage across the diode is 0.7 volts and the supply voltage is 2 volts, then the voltage across the resistor will be 1.3 volts.

### 2. **Voltage across the Resistor V**_{R}:

_{R}

You can find the voltage across the resistor using Ohm’s law.

### 3. **Voltage across the Diode V**_{D}:

_{D}

You can find the voltage across the diode by the Shockley diode equation.

### Putting it all together:

From KVL:

This is a nonlinear equation and we can solve it either numerically or using iterative methods.

### Simplified Case (For Forward Biased Diode):

In the case of a forward-biased diode where I≫IS, the voltage drop across diode VD diode equation can be approximated as:

Where V_{on} is the forward voltage drop of the diode.

The voltage drop across a silicon diode is 0.7 V and 0.3 V for a germanium diode when diodes are in a conduction state, therefore you can write the diode current formula as,

This is the basic and most practical formula for calculating the current through a diode in a series circuit with a resistor.

### Solved Example

A diode with a forward voltage drop of V_{D}=0.7 is connected in series with a 1kΩ resistor to a 5V power supply. Calculate the current flowing through the diode.

**Given:**

- Supply voltage, Vsupply=5 V
- Diode forward voltage, VD=0.7
- Resistor, R=1 kΩ=1000 Ω

**Formula:**

The current I in the circuit is calculated using Ohm’s Law, considering the voltage drop across the resistor.

**Solution:**

- Subtract the diode’s forward voltage drop from the supply voltage to get the voltage across the resistor:

- Now, apply Ohm’s Law to find the current through the diode:

The current flowing through the diode is 4.3 mA.