Secondary Switch Timing for Zero-Voltage Switching Power Supplies
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Solution Overview
Problem
Conventional switching mode power supplies face challenges in achieving higher power density and efficiency due to the limitations of battery capacity and the need for electrical isolation, particularly in fast-charging technologies, where increasing switching frequency and reducing passive component size are essential.
Innovation Solution
A switching mode power supply with a secondary control circuit that controls the secondary switch circuit to freewheel current in both directions, enabling zero voltage switching at the primary side by turning on the secondary switch circuit twice in each cycle, utilizing a secondary control signal to manage current flow and reduce power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If switching frequency is increased to reduce passive component size, then power density is improved, but power loss increases and efficiency deteriorates
Solution Approach 1:
The secondary switch circuit is turned on in advance before the primary power switch turns off, during the dead time period. This preliminary action ensures that the body diode is already conducting when the primary switch turns off, enabling zero voltage switching and avoiding voltage spikes and power loss that would occur with conventional switching timing.
Solution Approach 2:
The secondary switch circuit is controlled to conduct periodically during each switching cycle's dead time period. This periodic conduction during the interval between primary switch turn-off and turn-on enables continuous zero voltage switching operation, reducing power loss while maintaining high switching frequency for compact design.
2Volume of moving object
If switching frequency is increased to reduce passive component size, then power density is improved, but efficiency deteriorates
Solution Approach 1:
The secondary switch circuit is activated in advance during the dead time before the primary power switch turns off. This preliminary activation ensures that when the primary switch turns off, the transformer leakage inductance energy is already being discharged through the body diode, preventing voltage spikes and enabling soft switching, thereby improving converter efficiency while maintaining high switching frequency for compact size.
Solution Approach 2:
The secondary switch circuit conducts periodically during each switching cycle's dead time interval. This periodic operation ensures that zero voltage switching is achieved in every cycle, continuously improving efficiency while allowing the use of high switching frequencies that reduce passive component size.
3Device complexity
If secondary switch circuit is turned on once after current freewheeling, then circuit complexity is reduced, but zero voltage switching cannot be achieved
Solution Approach 1:
The switching control is segmented into two distinct phases: the first turn-on of the secondary switch circuit for current freewheeling after primary switch turn-off, and the second turn-on during the dead time before primary switch turn-on. This segmentation enables precise control of the body diode conduction timing, ensuring zero voltage switching is achieved while maintaining relatively simple control circuitry.
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
The implementation of zero voltage switching reduces power loss and enhances efficiency, allowing for higher power density and improved performance in fast-charging applications.
Implementation Method 1
a primary power switch, coupled to a primary side of an electrical isolation device... a secondary switch circuit, coupled to a secondary side of the electrical isolation device
Data Source
AI summary
A switching mode power supply with zero voltage switching is discussed. It adopts a first secondary signal generator and a second secondary signal generator to control a secondary switch circuit to be turned on once again after a current freewheeling process is over.