Switched-Mode Power Supply Current Control via Series Resistor
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Solution Overview
Problem
Switched mode power supplies (SMPS) face challenges in accurately controlling the average current delivered to loads, particularly in applications like LED lighting, where precise current management is required to optimize efficiency and reduce energy loss, especially in configurations like buck converters where monitoring and control mechanisms are complex.
Innovation Solution
The method involves using a switching transistor with a series resistor and inductor to monitor the load current by measuring voltage across the resistor, and controlling the switching transistor based on these measurements to maintain a predetermined average current, employing a controller circuit that includes a voltage-to-current converter and a pulse generator to adjust switching times according to the load's current needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedback loop is used to control current or voltage in an SMPS, then the precision of current control is improved, but the device complexity increases due to additional monitoring and control circuits
Solution Approach 1:
The patent implements a feedback mechanism where the controller circuit continuously monitors the current through the load (using voltage measurement across the series resistor) and adjusts the switching transistor's duty cycle accordingly. This closed-loop feedback system maintains precise current control by comparing the measured current with the desired current level and dynamically adjusting the switching parameters to eliminate any deviation.
Solution Approach 2:
The patent introduces a series resistor as an intermediary element that enables current measurement through voltage monitoring. Instead of directly measuring current (which would require complex current sensors), the system uses the voltage drop across the small series resistor as a proxy measurement, simplifying the monitoring circuit while maintaining measurement accuracy.
2Measurement precision
If the switching transistor is switched on and off frequently to control average current, then the current control precision is improved, but the energy loss increases due to switching losses
Solution Approach 1:
The patent employs periodic switching of the transistor with variable duty cycles to control the average current. By adjusting the ratio of on-time to off-time in each switching cycle, the system achieves precise average current control without requiring excessively high switching frequencies. The controller modulates the duty cycle based on feedback to maintain the desired average current while minimizing switching losses.
Solution Approach 2:
The patent implements dynamic adjustment of the switching parameters (duty cycle and switching timing) based on real-time current measurements. The controller continuously adapts the switching waveform to maintain optimal efficiency, reducing switching frequency when high precision is not required and adjusting the duty cycle dynamically to match load conditions, thereby minimizing unnecessary switching losses.
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 approach allows for precise control of the average current through the load, enhancing efficiency and reducing energy loss by continuously monitoring and adjusting the switching transistor's operation, which is particularly beneficial in SMPS configurations like buck converters used in LED lighting applications.
Implementation Method 1
measuring comprising monitoring a voltage across the series resistor
Data Source
AI summary
In accordance with an embodiment, a method of operating a switched-mode power supply includes receiving power from an input node via a first transistor, providing a first portion of the received power to a load via a switching transistor having a first terminal coupled to the first transistor and a second terminal coupled to the load via a series resistor and a series inductor, measuring a current through the load, measuring comprising monitoring a voltage across the series resistor; and controlling an average current through the load by switching on and switching off the switching transistor according to the measured current.