Flyback Converter Active Clamp Reduces EMI
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Solution Overview
Problem
Flyback converters face challenges in reducing electromagnetic interference (EMI) due to high power levels and increasing operating frequencies, which result in high-order harmonics and inefficient snubber circuits that waste energy and are problematic in resonant and quasi-resonant converters.
Innovation Solution
The implementation of an active clamp circuit with variable timing, specifically frequency dithering, to absorb noise from switching discontinuities, recirculate wasted energy, and spread radiated emissions across a wider spectrum, minimizing switching losses and EMI while maintaining converter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If snubber circuits are used to absorb high frequency transients, then electromagnetic interference is reduced, but energy is wasted due to inefficiency
Solution Approach 1:
The patent converts the harmful high frequency transients into beneficial recirculating energy flow. The active clamp circuit captures the transient energy that would normally be dissipated as heat in snubber resistors, and redirects it through the active switch back into the circuit, where it can be utilized or safely dissipated through the resonant tank. This transforms the harmful EMI-generating transients into a useful energy recovery mechanism.
Solution Approach 2:
The patent changes the operational parameters of the circuit by introducing active switching control with variable duty cycle. Instead of passive energy dissipation, the system actively controls the timing and duration of the clamp switch, adjusting the duty cycle dynamically to optimize both EMI reduction and energy efficiency. This parameter control enables the system to adapt to different operating conditions while maintaining efficiency.
2Volume of moving object
If operating frequency is increased to reduce component size, then inductor and capacitor values are reduced, but high order harmonics increase causing more EMI
Solution Approach 1:
The patent applies periodic active clamp switching synchronized with the resonant oscillations of the circuit. By timing the clamp switch activation to coincide with specific phases of the resonant cycle, the system periodically captures and redirects the high frequency transients. This periodic action effectively suppresses the harmful harmonics generated at high operating frequencies while maintaining the benefits of reduced component size.
Solution Approach 2:
The system employs feedback control through the active clamp circuit that responds to the instantaneous voltage and current conditions in the circuit. The clamp switch is activated based on feedback from the resonant tank voltage, creating a closed-loop control mechanism that dynamically suppresses EMI-generating harmonics. This feedback ensures that the high frequency transients are consistently managed regardless of operating conditions.
3Object-affected harmful factors
If spectral spreading is used to reduce EMI, then noisy signals are spread over wide bandwidth, but timing alignment with resonant signal troughs is compromised
Solution Approach 1:
The patent introduces dynamic timing control where the active clamp switch duty cycle and timing are continuously adjusted based on the resonant cycle phase. Rather than fixed timing, the system dynamically adapts the clamp activation moments to maintain optimal alignment with resonant troughs while simultaneously achieving spectral spreading. This dynamic adjustment allows the system to preserve timing reliability while reducing EMI through spreading.
Solution Approach 2:
The system performs preliminary action by proactively activating the clamp switch before the resonant voltage reaches its peak, anticipating the need for EMI suppression. The timing is pre-coordinated with the expected resonant cycle phases, allowing the clamp to be activated at optimal moments without disrupting the overall timing alignment. This preliminary action ensures both EMI reduction and timing reliability are maintained.
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 approach effectively reduces radiated emissions below EMI thresholds, minimizes switching losses, improves converter stability, and reduces output ripple, making it well-suited for resonant and quasi-resonant converters with high resonant frequencies.
Implementation Method 1
a resonant tank including an inductance in series with a capacitance, the resonant tank having a resonant frequency
Implementation Method 2
A second jitter delay spreads a second pulse width of the second pulse to reduce an amplitude of the radiated emission below an electromagnetic interference limit
Data Source
AI summary
A method for reducing electromagnetic interference in a flyback converter includes activating a first switch to generate a primary current therein. The first switch is deactivated to generate a secondary current from a magnetic flux generated by the primary current. The magnetic flux is removed by the generation of the secondary current. A second switch is activated with a first voltage pulse to limit an excess voltage across the first switch. The excess voltage is generated in response to the deactivation of the first switch. A second switch is activated with a second voltage pulse to limit a voltage oscillation across the first switch. The voltage oscillation occurs after the removal of the magnetic flux. A first pulse width of the first voltage pulse is increased by a first jitter delay. A second pulse width of the second voltage pulse is increased by a second jitter delay.