In many electronic devices, there are many electrical devices that require the supplied current to be kept constant. Generally, this kind of power supply that can provide constant current to the load is called a constant current source. The so-called cross-current of charging IC does not mean that the current value is absolutely unchanged, but the change is relatively small, and it maintains sufficient stability within a specified working range. How is the cross-current of charging IC achieved? Let‘s listen to Li Microelectronics to explain:

Constant current sources are often used in LED circuits. The basic constant current source circuits can be divided into three categories: transistor constant current sources, field effect transistor constant current sources, and integrated op amp constant current sources.

1. Transistor constant current source: This type of constant current source uses a transistor as the main component. The change of the collector voltage of the transistor has little effect on the current, and the current negative feedback is used in the circuit to improve the constancy of the output current. Usually, Certain temperature compensation and voltage stabilization measures are also adopted.

2.the field effect transistor constant current source: a constant current circuit composed of field effect transistors as the main component, the field effect transistor of this constant current source circuit is JEFT, ultra-low noise, the output current is determined by JEFT, and the detection voltage is related to JEFT .

3. the integrated op amp constant current source: In order to accurately output the current, an op amp is usually used as feedback, and a field effect transistor is used to avoid errors caused by the be current of the triode.

I understand how the charging IC achieves cross-current, but some people still ask about the LED drive power supply, how to distinguish between a constant voltage source and a constant current source, Hao Qi Core Technology will teach you a little trick. You can look at the output voltage parameter: if Its voltage is nominally a constant value, it is a constant voltage source. If it is a range value, it is a constant current source. For example, if there is a power supply whose output voltage is 12V, it is determined that this is a constant voltage source. If its nominal value is 30-70V, then it is a constant current source.