DC-DC Converter Mode Control for Light Load Efficiency
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Solution Overview
Problem
Power factor correction (PFC) circuits face inefficiencies at light loading conditions due to high switching losses and increased operating frequency in critical conduction mode (CRM), and existing solutions for transitioning to discontinuous conduction mode (DCM) require additional components and increase complexity and cost.
Innovation Solution
A control circuit that calculates a threshold time value based on peak inductor current and duty cycle to switch between CRM and DCM operation, eliminating the need for external current sense resistors and reducing switching losses by enforcing a minimum inductor peak current through intelligent switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If critical conduction mode (CRM) is used for PFC circuit operation, then power factor correction is achieved, but switching losses increase and operating frequency increases at light loading conditions
Solution Approach 1:
The patent implements dynamic mode switching between CRM and DCM based on load conditions. The control circuit monitors the load current and automatically transitions between conduction modes to optimize performance: CRM is used when high power factor correction is needed, while DCM is used at light loads to reduce switching losses and operating frequency, thereby resolving the contradiction between maintaining power factor correction and reducing energy losses.
Solution Approach 2:
The patent changes the operating parameters of the PFC circuit by switching between different conduction modes. By adjusting the conduction mode parameter based on load conditions, the circuit achieves optimal efficiency at different operating points, reducing switching losses and operating frequency at light loads while maintaining effective power factor correction at higher loads.
2Power
If separate interleaved CRM boost converters are used for higher power applications, then higher power capability is achieved, but cost and complexity increase due to phase synching requirements
Solution Approach 1:
The patent merges multiple PFC converter stages into a single integrated circuit implementation. By combining the functions of multiple interleaved converters into one unified device with integrated control, the patent achieves high power capability without the external complexity of phase synching circuits, reducing both cost and device complexity while maintaining the benefits of interleaved operation.
Solution Approach 2:
The patent creates a universal PFC controller that can operate in multiple modes (CRM, DCM, and burst mode) and handle various power levels through a single integrated device. This multi-functional approach eliminates the need for separate control circuits for different operating conditions, reducing overall system complexity and cost while maintaining high power capability.
3Loss of energy
If interleaved operation of two converters using DCM control for light loads is implemented, then light loading efficiency is improved, but cost and complexity increase with respect to phase synching
Solution Approach 1:
The patent implements self-service control where the integrated controller automatically monitors load conditions and switches between CRM and DCM modes without requiring external phase synching circuits. The controller uses internal sensing and control logic to achieve efficient light-load operation, eliminating the need for complex external synchronization hardware while maintaining improved light-loading efficiency.
4Productivity
If peak current measurement is implemented to trigger transition from CRM to DCM, then mode switching is achieved, but cost increases due to added sense resistor and integrated circuit pin
Solution Approach 1:
The patent extracts the peak current measurement function from external components and integrates it directly into the control circuit. By incorporating built-in current sensing capabilities within the integrated controller, the patent eliminates the need for external sense resistors and additional IC pins, reducing component count and cost while maintaining accurate mode switching capability based on peak current detection.
Data Source
AI summary
Disclosed examples include methods and control circuits to operate a single or multi-phase DC-DC converter, including an output that turns a first switch on for a controlled on time and then turns the switch off for a controlled off time in successive control cycles, as well as a PWM circuit that computes a threshold time value corresponding to a predetermined peak inductor current and a duty cycle value, and computes a first time value according to an error value for a subsequent second switching control cycle. The PWM circuit sets the on time to the first time value to operate in a critical conduction mode for the second switching control cycle when the first time value is greater than or equal to the threshold time value, and otherwise sets the controlled on time to the threshold time value for discontinuous conduction mode operation in the second control cycle.