Croatia the switching frequency of the AC-DC switching power supply module?(4)

When testing electronic and electrical equipment, the electronic and electrical equipment shall be tested for conducted interference voltage emission at its LED advertising screen power supply terminal. Although the test frequency bands of different standards are different, the test frequency bands of most products are 150K~30M. It can be seen from the lower limit of the test frequency that the operating frequency of the switching LED advertising screen power supply is close to 150K, and the more difficult it is to deal with the conducted disturbance.

input protection circuit
General module power products have built-in filters, which can meet the requirements of general power supply applications. If a more demanding power system is required, an input filter network should be added. An LC or π-type network can be used, but care should be taken to choose a smaller inductance and larger capacitance as much as possible.
In order to prevent the transient high voltage of the input power supply from damaging the power supply of the module, it is recommended that the user connect a transient absorption diode at the input end and use it with a fuse to ensure that the module is within a safe input voltage range. In order to reduce common-mode noise, Y (Cy) capacitors can be added, and a few nf high-frequency capacitors are generally selected. R is a fuse, D1 is a protection diode, and D2 is a transient absorption diode (P6KE series).

3. What special applications are required for the power switching frequency?

In some special cases, the circuit operation is more sensitive to the switching noise of the LED advertising screen power supply. Such as power carrier, wireless communication, wireless identification, etc. The LED advertising screen power supply requirements for power carrier applications are as follows.

At present, the power carrier is mainly used for intelligent carrier in the home, remote meter reading system, and remote street lamp control system. The use range of the carrier frequency of power lines in my country is 9KHz ~ 500KHz, and the carrier bandwidth is 4KHz. The development of power carrier is very limited due to the change of power line impedance and the interference of power line noise. In order to increase the communication distance of the power carrier, we must move away from the power switching frequency of the circuit carrier unit. The carrier frequencies currently used in China are 115KHz and 132KHz. In this case, the switching frequency is around 60KHz for the LED advertising screen power supply.