Current Estimation Circuit for Switching Power Supplies
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Solution Overview
Problem
Existing switching power supply devices face challenges in accurately estimating inductor current due to varying inductance values, leading to increased power loss and cost, particularly when using multiple ACCTs for current detection, which also increases switching loss and wiring inductance.
Innovation Solution
A current estimation circuit that includes current detection means, a capacitor for charging and discharging, and a differentiating circuit to calculate the amplification and reduction factors of the terminal voltage, allowing for accurate estimation of inductor current without needing separate current detection in the off period, thereby reducing costs and switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current detecting resistor is used to detect inductor current, then the current can be detected, but the power loss increases and conversion efficiency decreases
Solution Approach 1:
The patent replaces the mechanical/electrical current detecting resistor with a magnetic field-based DCCT (Direct Current Transformer) incorporating a Hall element. This substitution eliminates the need for current to flow through a resistive element, thereby detecting current through magnetic field sensing without the associated I²R power losses.
Solution Approach 2:
The patent introduces a Hall element as an intermediary sensing component that indirectly measures current by detecting the magnetic field generated by the current flow, rather than directly measuring voltage drop across a resistor. This intermediary approach enables current detection without the power loss inherent in resistive sensing.
2Loss of energy
If a DCCT incorporating a Hall element is used instead of a current detecting resistor, then power loss is reduced, but the device cost increases
Solution Approach 1:
The patent employs a self-service approach where the control circuit itself performs current estimation by calculating inductor current from readily available voltage signals and known circuit parameters, eliminating the need for expensive external current sensing components like DCCTs while maintaining accurate current information for control purposes.
3Measurement precision
If multiple ACCTs are used for current detection, then current detection capability is improved, but switching loss and wiring inductance increase
Solution Approach 1:
The patent extracts the current detection function from separate physical current transformers and relocates it to the control circuit through mathematical calculation. By taking out the need for physical current sensing components and performing current estimation computationally using existing voltage measurements and circuit parameters, the patent eliminates the switching losses and wiring inductance associated with multiple ACCTs.
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
This solution enables accurate inductor current estimation despite varying inductance values, reducing power loss and cost by eliminating the need for additional current detection components and minimizing switching losses.
Implementation Method 1
a capacitor 201 that is charged by a signal voltage from the current detector circuit 300
Implementation Method 2
utilizing an energy accumulation and releasing action of an inductor 4 accompanying a turning on and off of a switching element 5
Data Source
AI summary
A current flowing through a switching element (5) of a power supply is detected by an AC current transformer (8), and a capacitor (201) is charged by a voltage corresponding to the current. A reduction factor of the terminal voltage of the capacitor in an off period of the switching element (5) is calculated based on an amplification factor of the terminal voltage of the capacitor, an absolute value of an instantaneous value of an input power supply voltage, and an instantaneous value of a direct current output voltage, and the capacitor is discharged so that the terminal voltage of the capacitor decreases by the reduction factor in an off period of the switching element (5). A current flowing through an inductor (4) is estimated from the terminal voltage of the capacitor.