Resonant Half-Bridge Flyback Control With Skipping Cycles for ZVS
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Solution Overview
Problem
Existing half-bridge flyback power converters face inefficiencies during light and middle load operations due to high switching losses and inability to achieve zero voltage switching (ZVS) and variable output voltage, especially when operating in discontinuous conduction mode.
Innovation Solution
A resonant half-bridge flyback power converter with a switching control circuit that generates a skipping cycle period when output power is below a threshold, reducing switching frequency and incorporating a resonant capacitor and transformer to achieve ZVS and programmable output voltage, thereby improving power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power converter operates in DCM with reduced pulse width at light load, then the output power is decreased, but the switching frequency increases and switching loss increases
Solution Approach 1:
The patent introduces a skipping cycle mechanism where the power converter alternates between normal switching cycles and skipping cycles. During skipping cycles, the low-side switch is not activated, eliminating the second pulse that causes excessive switching. This periodic action between normal and skipping cycles allows the converter to maintain output power while reducing average switching frequency and switching loss at light load conditions.
Solution Approach 2:
The patent dynamically changes the switching pattern parameter by introducing a skipping cycle period based on output power level. When output power is below a threshold, the controller transitions from continuous switching to skipping cycles, effectively changing the operating parameters to reduce switching frequency and associated losses while maintaining adequate power delivery.
2Reliability
If the low-side switch toggles on/off twice during a switching cycle to achieve ZVS, then ZVS is achieved for the high-side switch, but the average switching frequency of the low-side switch increases significantly causing switching loss and heat
Solution Approach 1:
The patent applies periodic action by introducing skipping cycles where the low-side switch remains off during entire cycle periods. This reduces the frequency of low-side switch toggling from twice per switching cycle to once every other cycle or less, significantly reducing average switching frequency and associated losses while maintaining ZVS capability during normal cycles.
Solution Approach 2:
The patent extracts or removes the second pulse of the low-side switch during skipping cycles, eliminating the unnecessary switching action that contributes to losses. By taking out this redundant switching event while retaining the essential ZVS function in normal cycles, the patent reduces overall switching loss without compromising reliability.
3Power
If the switching frequency is increased to maintain power delivery at light load, then the power delivery is maintained, but the switching loss and heat generation increase
Solution Approach 1:
The patent uses periodic skipping cycles to reduce the average switching frequency and associated heat generation while maintaining adequate power delivery. By alternating between normal cycles (for power delivery) and skipping cycles (for heat reduction), the system maintains power delivery capability while reducing overall heat generation through reduced switching activity.
Solution Approach 2:
The patent dynamically adjusts the switching pattern based on load conditions. At light load, it transitions to skipping cycles to reduce switching frequency and heat generation. This dynamic adaptation allows the system to optimize between power delivery and heat management based on real-time operating conditions.
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 solution significantly reduces switching losses and heat generation, enhancing power efficiency for both light and middle load operations by skipping pulses during the skipping cycle period and extending the ZVS period, allowing for efficient operation with variable output voltage.
Implementation Method 1
a transformer and a resonant capacitor which are connected in series and are coupled to the half-bridge circuit
Implementation Method 2
a transformer and a resonant capacitor which are connected in series and are coupled to the half-bridge circuit
Data Source
AI summary
A resonant half-bridge flyback power converter includes: a first transistor and a second transistor which form a half-bridge circuit; a transformer and a resonant capacitor connected in series and coupled to the half-bridge circuit; and a switching control circuit configured to generate a first driving signal and a second driving signal to control the first transistor and the second transistor respectively for switching the transformer to generate an output voltage. The first driving signal is configured to magnetize the transformer. The second driving signal includes at most one pulse between two consecutive pulses of the first driving signal. The switching control circuit generates a skipping cycle period when an output power is lower than a predetermined threshold. A resonant pulse of the second driving signal is skipped during the skipping cycle period. The skipping cycle period is increased in response to the decrease of the output power.