The rapid development of the communications industry has greatly promoted the development of communication power supply, switching power supply in communication is the core of the system and power supply system has become the mainstream of modern communication. In communications, usually referred to as a high-frequency power converter, and the DC - DC (DC-DC) converter is called the secondary power supply. With the development of large scale integrated circuits, power supply module requires small, and therefore need to continuously improve the switching frequency and a new circuit topology, which high-frequency switching power supply technology for a higher requirement.
An advantage of high-frequency switch power
(1) Small size, light weight
High frequency power transformer replaced the traditional large and heavy in the frequency transformer, making the power more and more smaller and lighter.
(2) high frequency
High operating frequency, the output filter circuit can achieve miniaturization.
(3) high power factor
High-frequency switching power supply circuits using active power factor correction, power factor up to 0.98, while the traditional power supply waveform distortion on the electric line of electronic equipment have serious interference.
(4) high efficiency, energy saving
High-frequency switching power supply efficiency is usually 88 to 95%, the traditional power usually under 70%.
(5), good dynamic response
High-frequency switching power supply high frequency, on the dynamic response of the load and the power grid is far superior to the traditional power supply.
The output ripple frequency switching power supply generally smaller than traditional power.
(7) low noise
High-frequency switching power supply operating frequency in the range of human hearing, the audible noise is much lower than conventional power.
(8) to facilitate expansion
High-frequency switching power supply commonly used modular structure, maintenance, expansion is convenient.
(9) easy and flexible configuration using reasonable
In modern communication systems, high frequency switching power supply module, the general N +1 power supply. That is required to meet the design load based on the rectifier module, add a module. Usually the same time N +1 power supply modules, current sharing. When one module is in problems, the total load shared equally by the other modules, so that power supply with high reliability.
2 communication frequency switching power supply technology, the latest developments
Communication with the high-frequency switching power supply technology can basically reflect the latest development in several ways: converter topology, modeling and simulation, digital control, magnetic integration, and manufacturing processes.
2.1 Converter Topology
Soft-switching technology, power factor correction technology and multi-level technology is a hot area in recent years, converter topology. Soft-switch technology can effectively reduce the switching losses and switching stress, help converter efficiency; use of technology can improve PFC AC / DC converter input power factor and reduce harmonic pollution on the grid; and multi-level technology is mainly used in communication power three-phase input converter, you can effectively reduce switch voltage stress. At the same time as the input voltage is high, the use of appropriate soft-switching technology to reduce switching losses, is a multi-level technology in the future is an important research direction.
In order to reduce the size of converter needs to improve the switching frequency and high power density, smaller size of the magnetic materials must be used and passive components, but will increase the frequency MOSFET switching losses and drive a significant increase in losses, while the soft-switch technology The application can reduce the switching losses. The current most widely used communication power project is active clamp ZVS technology, the early 20th century, the birth of 90 phase-shift full-bridge ZVS technique and the late 90's synchronous rectification.
(1) ZVS active clamp
After three generations of active-clamp technique, and have declared a patent. VICOR Corporation on behalf of the United States the first active clamp ZVS technology, the operating frequency of DC-DC up to 1 MHZ, the power density close to 200 W/in3 However, the conversion efficiency does not exceed 90%. The first generation of active clamp to reduce the cost of technology, IPD company declared a second-generation active-clamp technology patents, which uses P-channel MOSFET, and is used in the transformer secondary side active clamp forward topology, This makes a lot of product cost reduction. However, this method forms the MOSFET of the zero voltage switching (ZVS) narrow boundary conditions, and the PMOS operating frequency is not ideal. In order to reset the magnetic energy in the core is not in vain when consumed, a Chinese-American engineer in 2001 and applied for a third-generation active-clamp technology patents, which is characterized in the second generation will be the core basis of the active clamp reset the energy released when transferred to the load, so to achieve a higher conversion efficiency. He has three circuit program: one program can use N channel MOSFET, and therefore a higher operating frequency, the use of the technology can be ZVS soft switching, synchronous rectification techniques together, which delivers up to 92% of its efficiency and power density of more than 250 W/in3.
(2) ZVS phase-shifted full-bridge
The mid-90s from the 20th century, ZVS phase-shifted full-bridge soft-switching technology has been widely used in the field of power supply. The MOSFET switching speed in less than ideal, the improvement of converter efficiency played an important role, but its shortcomings are many. The first disadvantage is that adding a resonant inductor, which led to a definite volume and loss, and the resonant inductor of the electrical parameters of the need to maintain consistency, which in the manufacturing process is more difficult to control; second drawback is that the effective duty cycle loss ratio. In addition, synchronous rectification make it easier to improve the efficiency of the converter, and phase-shifted full-bridge secondary-side synchronous rectification control performance is not satisfactory. The initial phase-shift PWM ZVS full-bridge controller logic required to provide accurate plus sub-pole synchronous rectifier control signal; today the latest phase-shift full-bridge PWM controllers such as the LTC1922 / 1, LTC3722-1/-2, although increase the secondary side synchronous rectifier control signal, but still can not effectively achieve the secondary side of the ZVS / ZCS synchronous rectification, but this is to improve the converter efficiency is one of the most effective measures. Another major improvement of the LTC3722-1/-2 can reduce the inductance of resonant inductor, which not only reduces the volume of the resonant inductor and its loss, the loss of duty cycle also been improved.