How to determine the current limiting resistor of LED and the common resistance of digital diode?

How to determine the current limiting resistor of LED and the common resistance of digital diode?

To answer this question, we need to first understand the working principles of light-emitting diodes and digital diodes.

Light emitting diode (LED) is a semiconductor component that can convert electrical energy into light energy. In LED, when electrons and holes combine through PN junction, photons are emitted, resulting in a light effect. However, the brightness of LED is directly proportional to the current density, and when the current density is too high, the LED will quickly burn out. Therefore, in order to protect the LED, it is necessary to use a current limiting resistor to limit the current density.

A digital diode is a device used to display numbers, consisting of multiple light-emitting diodes, each representing a number or character. There are two types of common resistors for digital diodes: common anode and common cathode. In a common anode digital diode, the anodes (positive poles) of all LEDs are connected together and connected to the positive pole of the power supply. In a common cathode digital diode, the cathodes (negative poles) of all LEDs are connected together and connected to the negative pole of the power supply. A common resistor is used to limit the current of each LED in a digital diode.

The method for determining the size of current limiting resistor and common resistor is as follows:

1. Determine the rated current and operating voltage of the LED

Before using LED, we need to consult its data manual to determine its rated current and operating voltage. In circuit design, we need to use these parameters to calculate the size of the current limiting resistor.

2. Calculate the size of the current limiting resistor

The design goal of the current limiting resistor is to ensure that the current density of the LED does not exceed its rated value. According to Ohm's Law, the size of the current limiting resistor can be calculated using the following formula:

R = (VSource - VLED) / ILED

Among them, R is the resistance value of the current limiting resistor, VSource is the voltage of the power supply, VLED is the operating voltage of the LED, and ILED is the rated current of the LED.

3. Choose the closest standard resistance value

The calculated current limiting resistance may be a non-standard value, so we need to choose the closest standard resistance value to design the circuit. The standard resistance values usually use E12, E24, or E96 series.

4. Calculate the size of the common resistance

The design goal of a common resistor is to make the current in each LED equal. We need to calculate the size of the common resistance based on the type of digital diode (common anode or common cathode) and the number of LEDs. If a common anode digital diode is used, the current of all LEDs needs to be added up, and then the size of the common resistance is obtained by subtracting the total current from the power supply voltage. If a common cathode digital diode is used, the total current needs to be divided by the number of LEDs to calculate the size of the common resistance.

In short, the process of determining the current limiting resistor and common resistor requires careful calculation and inspection. Accurately calculating these resistors can ensure that the circuit works properly, prevent LED from being over driven and burned out, and ensure that the brightness displayed by each LED in the digital diode is consistent.