LLC voltage regulators are widely used in power supply design, especially in high-performance power supplies. For example, LLC voltage regulators can be applied to server power supplies, industrial power supplies, and communication power supplies. Furthermore, LLC voltage regulators can also be used in electric vehicle charging stations and solar inverters.
The LLC resonant converter is a high-efficiency power converter used for voltage stabilization. This article details the principle, operation, and application of the LLC resonant converter in voltage stabilization. The LLC resonant converter is a topology based on a resonant circuit, mainly composed of capacitors, inductors, and switching transistors. Its working principle is to regulate the output voltage by controlling the switching transistors to turn them on and off. The working process of the LLC resonant converter is described in detail below. The resonance process of the LLC resonant converter mainly consists of two stages: resonant capacitor charging and resonant capacitor discharging. In the charging stage, when the switching transistor is on, the inductor discharges, transferring electrical energy to the output capacitor, while the resonant capacitor begins to charge. In the discharging stage, when the switching transistor is off, the inductor begins to store energy, while the resonant capacitor begins to discharge, transferring energy to the load.
LLC resonant converters can operate in two modes: continuous conduction and intermittent conduction. In continuous conduction mode, the switching transistor remains on until the resonant capacitor voltage drops to zero, at which point the inductor current is negative. This ensures that the inductor current is continuous throughout the entire operating cycle, thus achieving zero-voltage switching (ZVS) operation.
In intermittent conduction mode, the on-time of the switching transistor is less than one resonant cycle. While the short on-time leads to intermittent inductor current, ZVS (Zero-Voltage-Side-Shift) operation is still achievable. LLC resonant converters offer numerous advantages, making them widely used in voltage regulation. The following section will introduce the application of LLC resonant converters in voltage regulation. LLC resonant converters provide high-efficiency power conversion. Because the resonant capacitor and inductor store and release energy during resonance, losses are minimal. Furthermore, LLC resonant converters can achieve ZVS operation, reducing power losses in the switching transistor and improving overall conversion efficiency.
LLC resonant converters can operate over a wide input voltage range, from tens to hundreds of volts. This makes them suitable for applications with large input voltage fluctuations, such as solar panels and wind power generation. LLC resonant converters feature fast dynamic response. Their resonant process enables rapid energy transfer and regulation, thus achieving rapid voltage regulation. This characteristic makes LLC resonant converters particularly suitable for applications requiring fast response, such as data centers and electric vehicles. Because LLC resonant converters can achieve ZVS operation, reducing power losses in the switching transistors, they reduce electromagnetic noise and interference. This makes them widely used in applications with strict requirements for electromagnetic noise and interference, such as medical equipment and communication equipment.
The LLC resonant converter is a high-efficiency, wide-operating-range, fast dynamic response, low-noise, and low-electromagnetic-interference power converter. Through the resonant process and ZVS operation, the LLC resonant converter can achieve stable voltage regulation. Its applications in voltage stabilization are very extensive, including solar panels, wind power generation, data centers, and electric vehicles. The application of LLC resonant converters will provide stable and reliable voltage output for various power systems.
To reduce switching losses of transistors and improve power supply efficiency, soft-switching technology is widely used, which includes two main methods: zero-voltage switching (ZVS) and zero-current switching (ZCS).
Zero-voltage switch (ZVS): The voltage of the switch is reduced to zero before it is turned on, and it remains at zero during the turn-off process.
Zero-current switch (ZCS): The current is controlled to zero at the instant the switch is turned on, and the current is gradually reduced to zero before it is turned off.
In order to make LLC resonant converters applicable to wide range of voltage inputs, a large number of scholars have conducted related research. Reference [6] achieves the maximum gain range of the circuit by establishing an accurate model of the LLC resonant converter, but this method does not fundamentally change the gain of the converter. Reference [7] adopts a flexible control method to switch the single-phase full-bridge LLC to a single-phase half-bridge LLC and keep the output voltage stable, thereby expanding the voltage gain range of the converter. However, the analog control circuit makes the duty cycle of the trigger pulse change at a fixed speed, and the hardware implementation is complicated. The LLC (LLC resonant converter) is a high-efficiency, high-performance power conversion technology that regulates the output voltage by controlling the switching frequency and phase shift. The following are the main methods of LLC control of output voltage:
Variable-Frequency Control (VFC): Adjusts the output voltage by changing the conduction frequency of the main switch. When the output voltage is low, a fixed-frequency phase-shift control is used; when the output voltage is high, variable-frequency control is used, meaning the operating frequency changes with the output voltage. Phase-Shift Control (PSC): Adjusts the output voltage by changing the phase difference between the main and auxiliary switches. Phase-shift control ensures zero-voltage turn-on (ZVS) for the lead diode, but the auxiliary switch struggles to achieve ZVS under light loads and may cause reverse recovery problems in the diode.
Startup Strategy: During startup, a high-frequency start-up is typically used to reduce the startup current and avoid excessive impact on the switching transistor. Protection Functions: To ensure the safe operation of the power supply and load equipment, LLC circuits usually include overload protection and overvoltage protection. Through the above methods, LLC can achieve a wide range of output voltage regulation while maintaining high efficiency and performance. It should be noted that the design and control of LLC requires consideration of various factors, including circuit parameters, control strategies, and protection functions, to ensure stable operation under various operating conditions.
LLC voltage regulation is primarily achieved by controlling the resonant frequency of the LLC resonant circuit. When the input voltage changes, the LLC power supply senses this change and adjusts the resonant frequency to maintain a stable output voltage. Specifically, when the input voltage increases, the LLC power supply lowers the resonant frequency to keep the output voltage constant. Conversely, when the input voltage decreases, the LLC power supply increases the resonant frequency to maintain a stable output voltage.
Besides controlling the resonant frequency, LLC power supplies can achieve voltage regulation in other ways. For example, a feedback control circuit can monitor the output voltage and adjust the parameters of the resonant circuit according to changes in the output voltage, thereby achieving a stable output voltage. Furthermore, a load current control circuit can be added to achieve stable regulation of the output current. LLC voltage regulation is an important technology for achieving stable output voltage. Voltage regulation can be achieved by controlling the resonant frequency of the resonant circuit, using feedback control circuits, and load current control circuits. With the increasing integration of power supplies, combo controllers combining PFC and LLC have become the mainstream high-performance power supply solution. LLC voltage regulation is widely used in power supply design to meet the needs of various fields.
