With the continuous maturity of switching power supply technology, its application field has been further expanded. Compared with the traditional series continuous regulated power supply, the switching power supply has been greatly improved in efficiency, electromagnetic pollution, volume and reliability. On the other hand, the latest solid-state FM broadcast transmitter has higher and higher requirements for power supply. With the maturity of switching power supply technology, the constant updating of components and the application of high reliability control chip, the requirements of FM broadcast transmitter can be fully met. At present, switching power supply is widely used as the energy support for the exciter and power amplifier in the solid-state FM broadcast transmitter. The future digital control and management put forward higher requirements for switching power supply. Intelligent, digital, small size and high reliability will be the development direction of switching power supply for FM broadcast transmitter.

Switching Mode Power Supply

The power supply is the power heart of the entire FM broadcast transmitter. Considering the electromagnetic compatibility between the equipment in the transmitter room, the overall efficiency of the transmitter, the reliability of the power supply and the daily maintenance, the switching power supply is undoubtedly the best choice for the power supply of the solid-state FM broadcast transmitter. The excellent characteristics of switching power supply are mainly reflected in the following aspects. First: smaller size. It can be integrated with the power amplifier. The switching frequency of several hundred kHz reduces the volume of the filter impedance element to the minimum, thus reducing the weight and volume of the transmitter and facilitating transportation and daily maintenance. Second: higher efficiency. Including the application of new devices such as power switches and MOSFETs, the switching technology of multiple circuit topologies of switching power supply is an important guarantee to reduce the loss and improve the efficiency of power supply system. Third: less electromagnetic pollution. The electromagnetic interference (EMI) filter circuit and relevant high peak pulse absorption circuit installed in the transmitter power supply are important guarantees that the current harmonics of the power supply meet the requirements. It can not only improve the load characteristics of the power supply to the power grid, reduce the serious pollution to the power grid, but also reduce the harmonic interference to other network equipment. Fourth, the reliability has been further improved. A variety of protection measures against lightning, induction or counterattack overvoltage and the use of printed circuit boards coated with three protection paints (moisture, salt and mold) can minimize the probability of failure.

Switching power supply application

The switching power supply is a power supply form that continuously controls the power switch tube to perform on-off operation at a certain frequency so that power can be supplied to the converter or load through energy storage elements (such as inductors and capacitors). The average output voltage or current can be controlled by changing the duty cycle, the switching frequency or the related phase. The switching frequency range of the switching power supply is from 20kHz to several MHz. For working occasions with power supply power greater than 90W, switching power supply usually adopts two-stage conversion mode. I.e., a power factor correction (PFC) control converter and a DC / DC converter. In particular, the power factor correction circuit should be mentioned here. It is set to ensure that the input voltage and current work in phase. As a result, the power factor is close to 1, and all apparent power is converted into active power, thus the system efficiency is improved. If there is no PFC correction circuit, the input current will be input to the switching power supply in the form of narrow pulse width and high peak value pulse, causing serious harmonic interference. These harmonic components not only do not provide any energy to the load, but also cause the transformer and other equipment to heat. Power factor correction circuits are divided into active and passive types. The switching power supply of FM broadcast transmitter mostly adopts active power factor correction circuit, which is composed of AC / DC converter with active power factor correction and independent DC / DC converter.