DC-DC Converter Mode Control Circuit Using Time Interval Measurement
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Solution Overview
Problem
Existing dc-dc converters face inefficiencies in mode switching between PWM and PFM modes, especially in discontinuous conduction mode, due to inaccurate current measurements, leading to reduced power efficiency and increased PCB footprint and material costs.
Innovation Solution
Implementing a mode control circuit that switches between PWM and PFM modes based on time intervals of quasi-periodic current waveforms, measured and compared to threshold values, allowing for precise mode control without additional current comparators and enabling all-digital, programmable, and scalable designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the coil current amplitude is measured at the midpoint of the rising current waveform to determine mode switching, then the approach is simple to implement, but the measurement becomes inaccurate in discontinuous conduction mode where current is clamped at zero
Solution Approach 1:
The patent changes the measurement parameter from current amplitude to time interval. By measuring the time duration of the current waveform instead of its amplitude, the system accurately determines mode switching conditions without being affected by the zero-current clamping in discontinuous conduction mode. This parameter transformation resolves the measurement accuracy issue while maintaining implementation simplicity.
2Area of stationary object
If smaller inductors are used to decrease PCB footprint and reduce bill of materials, then the device size and cost are reduced, but the coil current slews faster increasing the trend towards discontinuous conduction mode where current measurements become inaccurate
Solution Approach 1:
The patent transforms the measurement approach from amplitude-based to time-based, which remains accurate even with faster current slewing in smaller inductors. The time interval measurement is independent of the slew rate, allowing the use of compact inductors without sacrificing measurement precision in discontinuous conduction mode.
3Measurement precision
If additional current comparators are added to accurately measure current in discontinuous mode, then measurement precision improves, but device complexity and bill of materials increase
Solution Approach 1:
The patent measures time interval instead of current amplitude, eliminating the need for additional current comparators. The time measurement can be performed using existing timing circuits or digital counters already present in most DC-DC converters, achieving accurate mode detection in discontinuous conduction mode without increasing device complexity or component count.
Data Source
AI summary
Representative implementations of devices and techniques determine when a dc to dc converter switches from a first mode of operation to a second mode of operation. The determination is based on a time interval representing a portion of a current waveform, which is measured and compared to a threshold value.