Low Power DC-DC Converter Cycle Control
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Solution Overview
Problem
Existing DC-DC converters experience low conversion efficiency and unstable operation at small input currents, particularly in the range of several μA to 100 mA, due to inadequate regulation loops, leading to high quiescent current consumption and inefficiency in charging storage capacitors or batteries from low power sources with high impedance.
Innovation Solution
A low power DC-DC converter design incorporating a converter stage with a low side switch and a rectifier switch, coupled with peak and zero current detectors, and a charge comparator to manage cycle time, allowing for accurate input current limit control and minimizing component count for efficient operation across varying capacities and inductances, without the need for complex regulation loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PWM control or continuous conduction mode is used, then regulation is maintained, but conversion efficiency deteriorates at small input currents
Solution Approach 1:
The patent implements periodic action by using a charge comparator that triggers cycle time based on accumulated charge thresholds. The converter operates in discrete charging cycles where the low side switch and rectifier switch are periodically activated, creating current peaks at controlled intervals rather than continuous operation. This periodic switching enables efficient operation at small input currents by eliminating continuous quiescent current consumption while maintaining regulation through cycle-time control.
2Loss of energy
If complex regulation loops are implemented, then conversion efficiency is improved, but device complexity increases
Solution Approach 1:
The patent extracts the essential regulation function from complex continuous control loops and implements it through a simplified discrete cycle-time control mechanism. Instead of using elaborate PWM controllers or continuous feedback loops, the invention extracts only the necessary charge accumulation detection and cycle triggering functions, implemented through a charge comparator that monitors integrated current and triggers switching cycles accordingly. This extraction maintains efficiency while dramatically reducing complexity.
Solution Approach 2:
The patent implements self-service through automatic cycle triggering based on charge accumulation. The charge comparator continuously monitors the integrated current and automatically triggers the next switching cycle when the threshold is reached, eliminating the need for external regulation loops or complex control circuitry. The system self-regulates its operation based on the actual charge transfer requirements, adapting automatically to varying load and input conditions without external intervention.
3Reliability
If DC-DC converter operates continuously, then regulation is maintained, but quiescent current consumption increases
Solution Approach 1:
The patent applies periodic action by transitioning from continuous operation to discrete cycling. The converter remains in a low-power standby state between charging cycles, with switches off and minimal quiescent current consumption. When charging is required, the system activates in controlled cycles triggered by the charge comparator, performing all necessary power transfer within discrete time windows. This periodic operation maintains regulation stability while minimizing average power consumption during idle periods.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining the charge accumulation function continuously through the charge comparator, even though power transfer occurs in discrete cycles. The integrated current signal continuously tracks the charge state, ensuring that the next cycle is always triggered at the appropriate moment to maintain continuous charge transfer to the output capacitor. This continuous monitoring ensures regulation stability without requiring continuous high-power operation.
Data Source
AI summary
A low power DC-DC converter includes a converter stage coupled to an input node, and having a low side switch and a rectifier switch. A peak current detector senses a current at the low side switch and a zero current detector senses a current at the rectifier switch. It is configured to set the low side switch to a non-conductive state and the rectifier switch to a conductive state if the peak current detector detects a predetermined peak current. It is configured to set the rectifier switch to a non-conductive state if the zero current detector detects zero current at the rectifier switch. A time interval between subsequent current peaks is triggered by a charge comparator receiving an average current fed to the low side and rectifier switches from the input node and a reference current coupled to the charge comparator by a reference current source.