Primary-Side Regulated PFM Controller for Audible Noise Reduction
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Solution Overview
Problem
Existing primary-side regulated Pulse Frequency Modulation (PFM) controllers in switching mode power supplies face issues with audible noise, poor transient response, and voltage drops at light loads due to low switching frequencies, which affect the efficiency and stability of battery-powered portable electronics charging.
Innovation Solution
A novel primary-side regulated PFM controller that adapts a peak current and frequency reduction scheme, utilizing a CS comparator, PFM control module, feedback error amplifier, and a reference voltage generating module with a time detector, peak current reference voltage generating unit, and error reference voltage generating unit to dynamically adjust peak current and frequency based on output loading, ensuring high conversion efficiency at light loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching frequency is reduced at light loads, then conversion efficiency is improved, but audible noise increases and transient response deteriorates
Solution Approach 1:
The patent implements dynamic switching frequency adjustment based on load conditions. The control circuit monitors the AC input voltage and dynamically adjusts the switching frequency of the primary switch: at light loads, frequency is reduced to improve efficiency; at heavy loads or transient conditions, frequency increases to reduce audible noise and improve transient response. This dynamic adaptation resolves the contradiction between efficiency improvement and noise reduction.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically based on operating conditions. A frequency adjustment circuit modifies the switching frequency in response to load variations and input voltage changes. At light loads, frequency is lowered to reduce switching losses; at higher loads or during transients, frequency is raised to maintain stable operation and reduce audible noise, thus resolving the efficiency-noise tradeoff.
2Loss of energy
If the switching frequency is reduced at light loads, then conversion efficiency is improved, but transient response deteriorates
Solution Approach 1:
The control circuit dynamically adjusts switching frequency based on real-time detection of input voltage and load conditions. During transient events or when input voltage varies, the circuit automatically increases switching frequency to maintain fast transient response. During steady-state light load operation, frequency is reduced to improve efficiency. This dynamic behavior resolves the contradiction between efficiency and transient response.
Solution Approach 2:
The patent implements parameter changes in switching frequency based on operating conditions. A frequency control mechanism adjusts the frequency parameter: lowering it at light loads for efficiency, and raising it during transients or voltage variations to maintain fast response. This adaptive parameter adjustment resolves the efficiency-transient response tradeoff.
3Ease of manufacture
If the peak current is kept constant, then circuit implementation is simple, but voltage drops occur at light loads due to cable resistance
Solution Approach 1:
The patent implements peak current adjustment based on load detection. The control circuit modifies the peak current parameter dynamically: at light loads, peak current is reduced to minimize voltage drops across cable resistance; at full load, peak current is maintained at design values. This selective parameter adjustment maintains voltage regulation reliability while keeping the circuit relatively simple.
Solution Approach 2:
The patent employs dynamic peak current adjustment based on real-time load detection. The control circuit adapts the peak current parameter to match actual load requirements, reducing it at light loads to eliminate voltage drops and maintaining it at higher values during heavy loads. This dynamic adaptation ensures reliable voltage regulation while preserving circuit simplicity.
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 effectively reduces audible noise, improves transient response, and maintains high conversion efficiency by dynamically adjusting peak current and frequency, addressing the limitations of prior art PFM controllers while keeping circuit implementation simple.
Implementation Method 1
a transformer T1 (including three windings: primary winding 101, secondary winding 102 and auxiliary winding 103)
Implementation Method 2
a primary switch 105
Implementation Method 3
a full bridge rectifier 107
Data Source
AI summary
A switching mode power supply, and a primary-side controlled PFM converter using the primary-side regulated PFM controller are discussed. In present embodiment, the primary side cycle by cycle switch peak current is no longer a constant. The time detector is added to monitor the waveform of primary-side sample voltage and then generate the duty cycle. The transfer function should be selected to satisfy a specific relationship of switching frequency and switch peak current against with output loading current. The new design shows higher switching frequency but lower value of switch peak current at light load condition. This resolves the audible noise and poor transient response issue from the prior art PFM controller.