Switched-Capacitor PWM Control Minimum On-Time Stability
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Solution Overview
Problem
Conventional DC-DC converters with inductor-based topologies face challenges in design considerations and efficiency, particularly at light loads, due to issues like board and component parasitics leading to unstable PWM performance and jittery operation.
Innovation Solution
An improved switched-capacitor (SC) converter topology without inductors, using a ladder SC circuit as a cap divider, which provides an unregulated output voltage fraction of the input voltage, and a PWM control scheme with a free-running OFF pulse that ensures a minimum ON pulse width, proportional to the OFF pulse, to maintain stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If inductor-based topologies are used in conventional DC-DC converters, then power conversion functionality is achieved, but board space increases and parasitic effects worsen
Solution Approach 1:
The patent removes the inductor component from the DC-DC converter topology, replacing it with a switched-capacitor architecture. This extraction of the problematic inductor element eliminates the associated parasitic effects and reduces board space requirements while maintaining the power conversion functionality through capacitor-based energy storage and transfer mechanisms.
Solution Approach 2:
The patent substitutes the magnetic field-based inductor mechanism with an electric field-based capacitor mechanism. This replacement changes the fundamental operating principle from magnetic energy storage to electric energy storage, eliminating inductor-related parasitics while achieving the same voltage conversion function through switched-capacitor networks.
2Reliability
If conventional inductor-based topologies are used, then voltage conversion is achieved, but PWM performance becomes unstable at light loads
Solution Approach 1:
The patent changes the operating parameters of the converter by using switched-capacitor topology with specific duty cycle control. The minimum on-time enforcement mechanism adjusts the timing parameters to ensure stable PWM operation across all load conditions, particularly preventing instability at light loads where conventional inductor-based converters struggle.
Solution Approach 2:
The patent implements feedback control through the minimum on-time enforcement mechanism that monitors and adjusts the PWM signal characteristics. This feedback ensures that the converter maintains stable operation by preventing excessively short on-times that cause instability at light loads, thereby improving overall reliability.
3Reliability
If minimum ON time is enforced in PWM control, then stability is improved, but control complexity increases
Solution Approach 1:
The patent implements minimum on-time enforcement by pre-configuring timing circuits that automatically prevent the PWM on-time from falling below a threshold value. This preliminary action is built into the control architecture, eliminating the need for complex real-time calculations or additional control algorithms, thereby maintaining simplicity while ensuring stability.
Data Source
AI summary
According to certain aspects, the present embodiments are based on an improved switched-capacitor (SC) converter topology that typically does not include an inductor. In particular, the topology includes a ladder SC circuit configured as a cap divider. The cap divider can be used to provide an unregulated output voltage Vout that is a certain fraction (e.g. 2) of input voltage Vin, such as Vin/2 (i.e., duty cycle≈50%). In some embodiments of a PWM control scheme for this topology, the PWM OFF pulse is free running, determined by the logic combination of timer and VOUT comparator. The PWM OFF pulse width is measured and used as the reference for a minimum PWM ON timer. The PWM ON pulse is therefore forced to be at least a minimum width that is proportional to the PWM OFF pulse. A UVOV protection window can be added to ignore the minimum PWM ON timer during a load transient.