Switching Power Converter Boundary Conduction Mode Control
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Solution Overview
Problem
Conventional digital control circuitry for switching power converters, especially in LED lighting applications, faces challenges in providing a wide range of output voltage and current while maintaining high switching frequencies, leading to increased cost and complexity, and often results in audible noise or reduced dimming capability.
Innovation Solution
The proposed solution involves operating the switching power converter in boundary conduction mode at low switching frequencies and transitioning to discontinuous conduction mode at higher frequencies, with the on-time of the switch adjusted based on desired output power, and clamping the on-time at a minimum to limit switching frequency and reduce control circuitry requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If digital control circuitry is used to maintain high switching frequencies for wide output voltage and current range, then output power capability is improved, but control circuitry complexity and cost increase
Solution Approach 1:
The patent dynamically switches between two conduction modes (CCM and DCM) based on operating conditions. The controller monitors the switching frequency and automatically transitions between modes to maintain optimal performance across different output power levels, thereby simplifying the control circuitry requirements while preserving wide output capability
Solution Approach 2:
The patent changes the conduction mode parameter based on switching frequency thresholds. By detecting when the switching frequency exceeds a predetermined threshold, the controller adjusts the operating mode to DCM, which allows for simpler control circuitry with fewer components while maintaining the required output power range
2Power
If switching frequency is increased to provide wide output voltage and current range, then output power capability is improved, but audible noise increases
Solution Approach 1:
The system dynamically adjusts the conduction mode based on the detected switching frequency. When the frequency enters the audible range (above the threshold), the controller transitions to DCM, which naturally limits the switching frequency and reduces audible noise while maintaining output power capability through adjusted duty cycle control
3Power
If boundary conduction mode is used with adjusted on-time for desired output power, then output power control is improved, but switching frequency may exceed limits causing control circuitry complexity to increase
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors the switching frequency and uses this information to determine whether to operate in CCM or DCM. This feedback loop ensures that the switching frequency remains within acceptable limits, preventing the need for complex high-frequency control circuitry while maintaining precise output power control
Solution Approach 2:
The controller dynamically selects the appropriate conduction mode based on real-time switching frequency measurements. By transitioning from CCM to DCM when the frequency threshold is exceeded, the system maintains output power control capability while avoiding the complexity associated with sustained high-frequency operation
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 relaxes the requirements on power converter control circuitry, allowing for cost-effective digital control implementations while maintaining a wide range of output voltage and current capabilities suitable for LED lighting, reducing audible noise and complexity.
Implementation Method 1
The transformer 12 includes a primary winding 20A coupled between an input node 22 and the switch 14 and a secondary winding 20B coupled between an anode of the diode 16 and ground. The current through the primary winding 20A induces a reverse current in the secondary winding 20B.
Implementation Method 2
The switch 14 may be a transistor such as a field-effect transistor (FET) including a gate (G) a drain (D), and a source (S). The switching control signal SC may be provided to the gate (G) of the switch 14 in order to control the amount of current flowing from the drain (D) to the source (S) thereof.
Implementation Method 3
The cathode of the diode 16 is coupled to an output node 24. This reverse current is blocked by the diode 16, and energy therefore accumulates in a magnetic field of the transformer 12.
Implementation Method 4
The capacitor 18 is coupled between the output node 24 and ground. This secondary winding current ISW charges the capacitor 18, which sources voltage and current to the output node 24 both when the switch 14 is open and closed in order to reduce ripple in the output voltage and/or output current.
Data Source
AI summary
A method of operating a switching power converter includes operating the switching power converter in a boundary conduction mode when a switching frequency of a switch in the switching power converter is below a switching frequency threshold such than an on time of the switch is adjusted based on a desired output power of the switching power converter, and operating the switching power converter in a discontinuous conduction mode when the switching frequency of the switch is above the switching frequency threshold such that one or more of the on time of the switch and a switching period of the switch are adjusted based on the desired output power of the switching power converter and the on time of the switch is clamped at a minimum switch on time.