Today, I will show you how the circuit of the LCD touch screen is designed: There are two main points when the LCD touch screen works: the driving circuit on the PCB substrate and the leads of the backlight. The electrical design related to the PCB substrate is the EMI design, and the electrical design of the backlight leads is the insulation withstand voltage design. This paper introduces the circuit design ideas of LCD touch screen from two aspects: EMI design and insulation withstand voltage design.

1. EMI of PCB substrate

EMI is the root cause of electrical interference. When designing a signal processing board, adequate electrical design countermeasures must be taken. The main method is to cover the substrate with a metal shield, or use a shielding strip to shield the impact of external electromagnetic interference on the substrate. In order to prevent the metal shielding layer from loosening and forming contact resistance, screws or contact pieces can be used for multiple connections. In addition, connecting the signal ground on the signal substrate to the board ground on the metal plate can also reduce the leakage of electrical interference to the outside. At the same time, conductive tape can also be used to strengthen the contact between sheet metal parts and substrates.

2. LED backlight insulation withstand voltage

LED backlights do not need high-voltage driving, while CCFLs require high-voltage driving of several thousand volts, so the dielectric withstand voltage design of the liquid crystal module is aimed at the structure of CCFL backlights. Insulation withstand voltage design requires that the structural design must meet the electrical insulation withstand voltage standards, as well as the requirements of the space distance and separation distance of the insulating medium. Specifically, it is necessary to clarify the maximum voltage specification of the wire of the lamp, pay attention to the maximum moving range of the high-voltage area and the insulating element, and the distance between the high-voltage area and the insulating element, and distances between  transformer coils, high-voltage terminals and conductive elements.

The above are the main points of circuit design ideas introduced from EMI design and insulation withstand voltage design. I hope it will be helpful to everyone~