Light-emitting diodes (LEDs for short) are solid-state light sources widely used in lighting, display, and communication. In the process of using LEDs, series and parallel are common circuit connection methods.

Series connection is to connect the positive and negative poles of multiple LEDs to form a continuous circuit. Parallel connection is to connect the positive poles of multiple LEDs to the positive poles and the negative poles to the negative poles to form multiple independent circuits.

The difference between series and parallel connection lies in the distribution of current and voltage. In a series connection, the positive and negative poles of each LED are connected together, and the current will be equal when passing through each LED. In a parallel connection, each LED becomes an independent circuit, and the current will be distributed among different LEDs. Therefore, the current distribution of series and parallel is different.

In a series connection, the current of the LED is evenly distributed among each LED. This means that each LED will receive the same current, and the current size depends on the total current of the entire series circuit. When multiple LEDs are used in a series connection, the total current is equal to the sum of the currents of each LED. For example, if each LED is rated for 20 mA and 5 LEDs are connected in series, the total current is 100 mA. Therefore, the series connection does not change the current distribution, but keeps the current stable in the entire circuit.

However, in a series connection, the voltage is added between each LED. Each LED has a rated voltage drop, which is the forward voltage drop. The forward voltage drop is the voltage that the LED needs to operate normally. The forward voltage drop depends on the material and color of the LED, and is usually between 2V and 4V. Therefore, in a series connection, the forward voltage drop of each LED will gradually add up, and the total forward voltage drop will increase. Taking the 5 LEDs mentioned above as an example, if each LED has a forward voltage drop of 3V, the total forward voltage drop will be 15V.

Unlike in series connection, the parallel connection of LEDs allows each LED to have the same voltage. If each LED has a forward voltage drop of 3V, then in a parallel connection, each LED will receive a voltage supply of 3V. The parallel connection does not change the voltage distribution, but keeps the voltage stable between each LED.

In addition to the different current and voltage distribution methods, the series and parallel connection methods will also affect the brightness, reliability and failure rate of the entire circuit. In a series connection, if one LED fails, the entire series circuit will not work properly. In a parallel connection, even if one LED fails, the other LEDs can still work normally because they are independent circuits.

In summary, the series and parallel connection methods of light-emitting diodes differ in the distribution of current and voltage. The series connection allows the current to be evenly distributed between each LED, but it will cause the forward voltage drop to be superimposed. The parallel connection allows each LED to have the same voltage, but the current will be distributed between each LED. These differences will affect the brightness, reliability and failure rate of the entire circuit. Therefore, in practical applications, it is necessary to select a suitable connection method according to specific needs.