Switching power supplies consume power in two main ways: fixed losses caused by parasitic resistances in semiconductor switches, magnetic components, and wiring, and switching losses that occur during the on/off process. Fixed losses are largely dependent on the intrinsic properties of the components, so reducing them requires advancements in component technology. For magnetic elements, researchers have long explored low-loss winding techniques that account for skin effect and proximity effect.
To reduce switching loss from transformer leakage inductance surges, new circuit technologies like snubber circuits with energy regeneration functions have been developed. Here are some key methods to improve the efficiency of switching power supplies:
(1) ZVS (Zero Voltage Switching) and ZCS (Zero Current Switching) use resonant switches to minimize switching losses. These techniques are highly effective but can increase peak current and voltage, which may lead to higher fixed losses.
(2) Edge Resonance techniques, such as active clamp circuits, help reduce switching loss. The active snubber is a practical ZVS method, but it can suffer from efficiency degradation under light load due to reactive currents.
(3) Extending the on-time of the switching element helps suppress peak current, thereby reducing fixed losses. This approach is particularly useful when using a tap inductor to manage leakage inductance surges.
(4) In low-voltage, high-current applications, improving the synchronous rectification circuit significantly reduces fixed losses. A two-stage structure is one common approach, where the first stage controls the output voltage, while the second stage manages the current. Although traditional thinking suggested this would lower efficiency, it has proven very effective in specific scenarios.
(5) Implementing parallel structures in the converter circuit, such as a Current Doubler, can also reduce fixed losses. This method allows for more efficient power distribution and better thermal management.
In summary, optimizing both fixed and switching losses is crucial for enhancing the performance of switching power supplies. Each technique has its own advantages and trade-offs, and selecting the right method depends on the application’s specific requirements.
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