Primary-Side Current Sensing in Forward Converters for LED Load Control
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Solution Overview
Problem
Existing forward converters for LED light sources require an optocoupler to control the magnitude of load current, which is costly and inefficient.
Innovation Solution
A forward converter design that utilizes a transformer, semiconductor switches, a capacitor, and a current sense circuit to control load current without an optocoupler, using a half-bridge inverter circuit and a current sense circuit to generate a load current control signal representative of the primary current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an optocoupler is used to control load current in a forward converter, then the control function is achieved, but the cost and device complexity increase
Solution Approach 1:
The patent removes the optocoupler from the forward converter circuit by extracting its isolation function and replacing it with a primary-side current sensing approach using a sense resistor and controller that directly monitors primary current to regulate load current without optical coupling
Solution Approach 2:
The controller performs multiple functions: it generates PWM signals for the semiconductor switch, monitors primary current through the sense resistor, and regulates load current based on this feedback, replacing what previously required separate optocoupler-based feedback circuitry
2Reliability
If an optocoupler is used to control load current, then isolation is provided, but efficiency decreases due to additional components
Solution Approach 1:
The patent replaces the optical isolation mechanism (optocoupler) with an electrical sensing and control mechanism using a sense resistor and primary-side current monitoring, eliminating optical component losses and improving overall conversion efficiency while maintaining control functionality
3Measurement precision
If a current sense circuit is added to the forward converter, then load current control precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the current sensing function with existing circuit elements by using a sense resistor integrated into the primary circuit path and processing the sense voltage through the existing controller, merging measurement and control functions into a unified primary-side regulation system rather than adding separate independent circuits
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 precise control of load current and intensity of LED light sources without the need for an optocoupler, improving efficiency and reducing costs.
Implementation Method 1
a transformer, a half-bridge inverter circuit, a capacitor, a controller, and a current sense circuit. The transformer may include a primary winding and a secondary winding adapted to supply current to the electrical load
Implementation Method 2
The capacitor may be electrically coupled between the junction of the first and second semiconductor switches and the primary winding of the transformer to cause a primary voltage across the primary winding
Data Source
AI summary
A load control device for controlling the amount of power delivered to an electrical load (e.g., an LED light source) includes first and second semiconductor switches, a transformer, a capacitor, a controller, and a current sense circuit operable to receive a sense voltage representative of a primary current conducted through a primary winding of the transformer. The primary winding is coupled in series with a semiconductor switch, while a secondary winding is adapted to be operatively coupled to the load. The capacitor is electrically coupled between the junction of the first and second semiconductor switches and the primary winding. The current sense circuit receives a sense voltage and averages the sense voltage when the first semiconductor switch is conductive, so as to generate a load current control signal that is representative of a real component of a load current conducted through the load.