1 Introduction
Compared with traditional linear power supplies, switching power supplies have the advantages of small size, light weight and high efficiency. Therefore, in recent years, more and more people have studied switching power supplies, and corresponding technologies have emerged in an endless stream. Researching low-cost, reliable, and compatible switching power supplies has become the goal of many power supply design engineers. This paper proposes a low-cost full-voltage design without APFC for high-power switching power supply. This scheme uses the automatic voltage doubler method to effectively reduce the range of the AC's DC input voltage, thus greatly reducing the power supply cost.
2. Full voltage power supply
Counting the world's AC voltage, you can divide the voltage into:
100V represented by Japan, 120V represented by the United States, 127V represented by Mexico, 220V represented by China, 230V in Europe, and 240V in Australia. Therefore, voltages in the world are distributed between 100V-127V and 220V-240V. . That is, if the switching power supply that satisfies the requirements of these two voltage segments can be considered as a full-voltage switching power supply. The switching power supply that realizes full voltage can be roughly divided into: ordinary stepless type, APFC stepless type, and automatic double voltage type.
2.1 Ordinary stepless
Ordinary stepless switching power supplies are widely used in small power switching power supplies. In a small power section of less than 300W, the designer usually adopts a 100-240V full-segment voltage scheme with both structure and cost. Although the structure is simple, high requirements are imposed on power devices (such as: AC adapters, switch tubes, and rectifier tubes). Since the increase of the device parameters in a certain range does not have much influence on the price, it is quite cost-effective in the small power section. As the power rises, the power supply places new demands on the power devices of each part. This requirement has great difficulties in terms of price and technology.
2.2 APFC stepless
The APFC is an active PFC that uses a dedicated PFC controller.
The circuit power component consists of a standard boost circuit that uses dual feedback of voltage and current, where the voltage is in the outer loop and the current is in the inner loop. Therefore, the APFC makes the waveform of the current sinusoidal while ensuring a constant voltage at the output.
The benefits of APFC are also obvious: 1 large increase in power factor; 2 compatible with input 100-240V full-section voltage; 3 EMC has a good improvement. Inadequacies:
1 volume and weight have increased; 2 power supply costs have increased by about 50%.
2.3 Automatic voltage doubler
In view of the various drawbacks of manual operation and the voltage laws of various countries in the world, the automatic voltage doubler is improved on the basis of the manual voltage doubler, and the automatic switching of the input voltage of the low voltage country is realized. The automatic voltage doubler switch can use relays, MOSFETs, IGBTs, and thyristors. Since the design is applied at a power frequency of 50-60 Hz, the zero-crossing requirements and production costs are considered.
The thyristor is selected as the switching device. SCR has great advantages in cost, and the response speed can meet the requirements.
3. System structure and principle
Basic power supply specifications: rated output 1200W, peak power 2400W; input voltage can be AC100-127V and 220-240V; output voltage is DC160V. The system meets global voltage compatibility, and has ultra-low standby power consumption of less than 0.3 watts.
3.1 System Structure
The whole system can be divided into main power part to supply power to the power amplifier part. The auxiliary power supply provides primary control circuitry and secondary control circuitry. The controller is used to realize the automatic voltage recognition and voltage doubler function, and at the same time, the MCU realizes the remote wake-up system function. The AC to DC rectification section, the auxiliary power supply and the main power supply are designed to be independently powered. In standby mode, the auxiliary power is removed from the main power rectification section, which provides a hardware basis for low standby power consumption.
3.2 main power supply
3.2.1 Main power supply design
The main power supply uses a phase-shifted full-bridge topology. The full-bridge circuit is easy to achieve high-power output, and the phase-shifted full-bridge is an improved version of the full-bridge circuit, which is more advantageous in terms of overall efficiency. A resonant inductor is connected in series in the bridge circuit, and the resonant inductor resonates with the parasitic output capacitance Coss of the MOS transistor. Therefore, the voltage at the DS terminal is zero between the turn-on of the MOS transistor, and zero voltage is turned on. Since the zero-voltage turn-on of the MOS transistor is realized, the requirements of the driving circuit and the Qg constant of the MOS transistor are lowered, so that the device cost is also reduced. A dual-image thyristor is used as a voltage doubler switch. A unidirectional thyristor disconnects the entire mains supply. When the thyristor is completely disconnected, all devices on the entire main power supply circuit have no current loop, and the leakage current of the thyristor itself is removed, and the main circuit has no power loss.
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