Experts talk about: constant current diode and its application in driving LED

Constant current diodes have been around for a long time, but this type of diode has not attracted attention because it is only used as a standard for current in some instruments. However, with the recent boom in the LED industry, this diode has suddenly attracted widespread interest. Many large foreign companies have developed such products to drive LEDs because LEDs must use constant current sources as the driving force. Below we will discuss in depth the performance and application of constant current diodes.

First, what is a constant current diode

The ideal constant current source is a device with an internal resistance of infinity, and the current flowing through it will never change regardless of the voltage across it. Of course this device is impossible to exist. The actual constant current diode is equivalent to a certain operating voltage range (for example, 25-100V), and its current is constant to a certain value (for example, 20mA). Its equivalent circuit is shown in Figure 1.

Figure 1. Equivalent circuit of a constant current diode

Its internal resistance is Z, and the capacitance in parallel is approximately 4-10pF. Its typical volt-ampere characteristics are shown in Figure 2.

Figure 2. Typical volt-ampere characteristics of a constant current diode