The basic structure of the LCD switching power supply circuit

At present, the switching power supplies used in LCDs are all parallel type, and there are two main forms of commonly used circuit structures:

(1) Control chip + single switch tube

The switching power supply adopts the circuit structure of control chip + single switch tube, which is most widely used in LCD switching power supplies. Its circuit block diagram is shown in Figure 1.

Figure 1 Control chip + single switch tube switching power supply circuit structure

Commonly used switching power supply control chips include UC38, KA38 series (such as UC3842, etc., in addition, FA13842 is the same as UC3842), TEA1533, ICE2AS01, SC*1, NCP1200AP40, L5991, etc. The power switch tube is located outside the control chip and can be a transistor or a field effect tube, but most of them are N-channel field effect tubes.

(2) The control chip contains a switch tube

Some switching power supply control chips have a high degree of integration. In addition to the functions of common power supply control chips, they also integrate the switch tube. Due to the large size and power of this type of switching power supply control chip, it is generally called a thick film circuit and requires a heat sink when installed.

Common models of control chips (thick film circuits) containing switching tubes include KA5M, KA55 series (such as KA5 M0365R), TOP series (such as TOP244, T0P247), etc., which have been used in some liquid crystal displays. The structure of this switching power supply is shown in Figure 2.

Figure 2 The structure of the switching power supply circuit with a switch tube inside the control chip