Transformerless Boost Regulator Current Sensing
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Solution Overview
Problem
Standard peak-current based controllers for boost converters fail to operate correctly when combined with charge pumps due to current corruption, limiting their use in applications like medical diagnostic ultrasound imaging and high-power car stereos, as they rely on grounded sense resistors which are affected by charge pump currents.
Innovation Solution
A current-mode controlled boost converter with separate current paths for sensing and charge pump operation, using a diode to block reverse current from the charge pump and an auxiliary switch to manage charge pump current, allowing accurate current sensing and preventing incorrect measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a standard peak-current based controller with grounded sense resistor is used in a boost converter combined with charge pump, then the circuit can be simplified and cost reduced, but the charge pump current corrupts the sensed current and the controller cannot operate correctly
Solution Approach 1:
The patent segments the current sensing path from the charge pump current path by introducing a separate sense resistor connected to the switching node. This allows the controller to measure only the inductor current through the sense resistor, while the charge pump current flows through a separate path that does not interfere with the sensing measurement.
Solution Approach 2:
The patent introduces an intermediary switching node and sense resistor configuration that mediates between the inductor current and the charge pump current. The sense resistor is placed in a position where it only senses the inductor current, while the charge pump connects to the switching node through a diode that prevents its current from flowing through the sense resistor, thus eliminating corruption.
2Power
If multiple inductors are used in superboost configuration to increase multiplication ratio, then the boost factor is improved, but parasitic resistances increase and complexity increases
Solution Approach 1:
The patent merges the functionality of multiple inductors into a single inductor by combining it with a charge pump circuit. The inductor operates in conjunction with the charge pump to achieve the same voltage multiplication effect that would require multiple inductors, thereby reducing component count and parasitic resistances while maintaining the desired boost factor.
Solution Approach 2:
The patent makes the single inductor serve multiple functions by combining it with the charge pump mechanism. The inductor not only performs its traditional energy storage function but also works synergistically with the charge pump to achieve high voltage multiplication, effectively replacing what would traditionally require multiple inductors in a superboost configuration.
3Measurement precision
If current sensing is performed in the supply path rather than ground return to avoid charge pump current corruption, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates an equipotential reference at the switching node by connecting the sense resistor between the switching node and ground. This allows the controller to accurately sense the inductor current without being affected by charge pump current, as the sense resistor is positioned at a node where only inductor current flows, establishing a clean measurement reference point.
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
Enables the use of common controllers for transformerless switching regulators, providing a high boost factor and accurate current sensing, reducing costs and complexity while supporting applications requiring programmable voltages greater than the supply voltage.
Implementation Method 1
A diode connects between the inductor and the input of the charge pump. The diode connects to prevent current from the charge pump entering the first transistor.
Implementation Method 2
An inductor of a boost converter is charged. During the charging, reverse current from a charge pump is blocked from reaching a current sensing path with a diode.
Data Source
AI summary
For transformerless switching regulators, a current-mode controlled boost converter operates based on current sensing through a switch to ground, allowing use of common controllers. To avoid reverse current from a cascaded charge pump, the input of the charge pump is blocked by a diode from passing through the switch to ground and is itself separately switched to ground.