PFC Circuit Auxiliary Switch Timing for Full-Range Zero-Voltage Switching
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Solution Overview
Problem
The conversion efficiency of PFC circuits is adversely affected due to the inability to realize zero voltage switching across the full voltage range, particularly in CRM and DCM modes, leading to lower efficiency.
Innovation Solution
A PFC circuit incorporating a boost inductor, auxiliary winding, auxiliary switch tube, main switch tube, clamping capacitor, series resistor, and control module with mutual inductance, where the control module coordinates the state changes of the auxiliary switch tube relative to the main switch tube to achieve zero voltage switching through appropriate timing and voltage detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the main switch tube is controlled in CRM mode with bus voltage higher than half of output voltage, then the bottom switching function is achieved, but zero voltage switching cannot be realized and conversion efficiency deteriorates
Solution Approach 1:
An auxiliary switch tube is introduced as an intermediary component between the main switch tube and the boost inductor. The auxiliary switch tube, controlled by a control module, enables zero voltage switching by providing an additional switching path that allows the main switch tube to turn on when the voltage across it is zero, even in CRM mode when bus voltage is high. This mediator component resolves the contradiction by enabling ZVS without compromising the bottom switching function.
2Device complexity
If the main switch tube is controlled to achieve bottom switching only, then the control is simplified, but the conversion efficiency is reduced due to inability to achieve zero voltage switching
Solution Approach 1:
The switching control function is segmented into two independent parts: the main switch tube handles the primary bottom switching function, while the auxiliary switch tube manages the zero voltage switching function. The control module independently controls each switch tube based on different conditions, allowing the system to maintain simplified overall control while achieving both switching functions simultaneously. This segmentation resolves the contradiction by separating the control responsibilities.
3Device complexity
If the PFC circuit operates in full voltage range without auxiliary switch tube, then the circuit structure is simple, but zero voltage switching cannot be realized across full voltage range
Solution Approach 1:
The auxiliary switch tube is activated in advance before the main switch tube needs to switch on, specifically when the voltage across the main switch tube reaches zero. The control module detects the zero voltage condition and turns on the auxiliary switch tube beforehand, creating the necessary conditions for the main switch tube to perform zero voltage switching. This preliminary action ensures ZVS capability across the full voltage range while maintaining a relatively simple circuit structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration ensures effective zero voltage switching across the full voltage range, enhancing conversion efficiency by coupling electric energy between the boost inductor and auxiliary winding, thereby improving the circuit's performance.
Implementation Method 1
the boost inductor and the auxiliary winding have mutual inductance
Data Source
AI summary
A PFC circuit includes: a boost inductor, an auxiliary winding, an auxiliary switch tube, a main switch tube, a clamping capacitor, a series resistor and a control module; the boost inductor and the auxiliary winding have mutual inductance, a first terminal of the auxiliary winding is connected to a first terminal of the auxiliary switch tube, a second terminal of the auxiliary switch tube is connected to a first terminal of the clamping capacitor, a second terminal of the clamping capacitor is connected to a first terminal of the series resistor, and a second terminal of the series resistor is connected to a second terminal of the auxiliary winding; the main switch tube is connected between the boost inductor and the ground; and the control module is respectively connected to a control terminal of the main switch tube and a control terminal of the auxiliary switch tube.