Freewheeling Diode Current Sensing for Buck LED Drivers
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Solution Overview
Problem
In non-isolated Buck converters, direct sensing of output current with a sense resistor in high side switches results in power dissipation and efficiency reduction due to the need for additional circuitry to level shift the reference, leading to increased heat dissipation and larger heat emission surfaces.
Innovation Solution
Simplified sense circuitry is introduced by sensing the output current in the path of the freewheeling diode, which shares a common reference level with the controller, reducing component count, heat dissipation, and size, and allowing for efficient current regulation in LED drivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used to directly sense output current in high side switches, then current regulation accuracy is improved, but power dissipation increases and efficiency decreases
Solution Approach 1:
The patent uses the freewheeling diode as an intermediary element to sense output current. Instead of placing a sense resistor directly in the high side switch path, the circuit senses current through the freewheeling diode's voltage drop, which naturally occurs during the switch's off-state. This intermediary approach allows current measurement without adding significant power loss to the main current path.
Solution Approach 2:
The freewheeling diode's inherent voltage drop during operation is utilized as the sensing mechanism. The diode's forward voltage (typically 0.7V for silicon diodes) serves as the sensing signal, eliminating the need for an external sense resistor. This self-service approach converts a necessary component's natural behavior into the sensing function, avoiding additional power dissipation.
2Measurement precision
If additional circuitry is added to level shift the reference voltage, then current sensing accuracy is improved, but device complexity increases
Solution Approach 1:
The patent combines the current sensing function with the existing freewheeling diode and controller ground reference. By sensing the voltage across the freewheeling diode with respect to the controller's ground (which is already at the same potential level), the design merges multiple functions into existing components, eliminating the need for separate level-shifting circuitry while maintaining accurate current measurement.
Solution Approach 2:
The sensing circuit is designed to measure voltage across the freewheeling diode with respect to the controller's ground reference, ensuring both points are at compatible potential levels. This equipotential approach eliminates voltage offset issues that would require level-shifting circuitry, as the sensing measurement is taken between two points that are already at the same reference potential.
3Measurement precision
If sense resistor is used with level shifting circuitry, then current regulation is achieved, but heat dissipation increases requiring larger heat emission surfaces
Solution Approach 1:
The freewheeling diode serves as an intermediary that naturally dissipates minimal heat while providing the sensing function. By utilizing the diode's inherent voltage drop rather than forcing current through a dedicated sense resistor, the design achieves current regulation with significantly reduced heat generation, eliminating the need for large heat emission surfaces.
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 enhances efficiency, reduces component count and size, and minimizes heat dissipation, making it suitable for compact designs like LED lamp bases, while maintaining effective current regulation.
Implementation Method 1
A typical way to measure the output current is to include a sense resistor at the output of the power converter such that the output current flows through the sense resistor. The resultant voltage across the sense resistor is proportional to the output current.
Implementation Method 2
In these examples, the output can be sensed indirectly through the use of an opto-coupler or magnetically coupled winding on the transformer core.
Implementation Method 3
In these examples, the output can be sensed indirectly through the use of an opto-coupler or magnetically coupled winding on the transformer core.
Data Source
AI summary
A current sense and feedback circuit is provided for a non-isolated Buck power converter to maintain constant current load regulation. The Buck converter may have a high side power switch and may include an input port, a switcher unit including a switch and a controller, an inductor coupled to the output, and a freewheeling diode for circulating the inductor current when the switch is open. The simplified current sense and feedback circuit of the power converter may include a current sense resistor module coupled to the freewheeling diode to provide a sense signal to the controller. The controller may also be coupled to the output of the power converter to sense an over voltage condition. The simplified current sense and feedback circuit may provide output regulation while maintaining a low component count, small size, and low loss that makes the power converter suitable for use in compact design applications.