SMPS Control Circuit for High Power Factor and Constant LED Current
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Solution Overview
Problem
Conventional switch mode power supply (SMPS) systems for LED lighting struggle with maintaining constant output current and achieving high power factor, especially when used with different AC power sources and dimmer circuits, failing to meet energy efficiency standards and requiring additional customization or circuits.
Innovation Solution
The SMPS system generates a phase reference signal in phase with the AC input current, controlling current pulses to maintain a constant average output current and high power factor, allowing operation across a wide range of AC input voltages without additional source selection circuits and accommodating dimmer circuits by adjusting energy transfer during specific AC cycle phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional SMPS is used to drive LED with different AC power sources (110V vs 220V), then the LED lighting device needs to be customized for local power sources with additional control circuits or power source selection circuits, but this increases device complexity and production cost
Solution Approach 1:
The control circuit is designed to universally support multiple AC input voltages (110V, 220V, and other voltages within a wide range) without requiring additional power source selection circuits. The circuit automatically adapts to different voltage levels through its inherent design, making the LED lighting device compatible with various regional power standards while maintaining simple circuit architecture.
Solution Approach 2:
The control circuit dynamically adjusts its operating parameters based on the detected AC input voltage level. By monitoring the input voltage and automatically modifying its control strategy, the circuit maintains optimal performance across different voltage conditions without requiring manual configuration or additional hardware for voltage selection.
2Loss of energy
If conventional LED lighting devices are used without power factor correction, then the circuit design is simpler, but the power factor is low and energy efficiency standards are not met
Solution Approach 1:
The power factor correction function is merged into the existing control circuit of the LED driver. Rather than adding a separate power factor correction circuit, the same control circuit that regulates LED current is used to shape the input current waveform and achieve high power factor. This integration eliminates the need for additional components while meeting energy efficiency standards.
Solution Approach 2:
The control circuit performs multiple functions simultaneously: it regulates the LED output current, corrects the power factor, and adapts to different AC input voltages. By making the control circuit multi-functional, the design achieves high power factor correction without increasing overall device complexity or requiring separate dedicated circuits for each function.
3Adaptability or versatility
If conventional LED lighting devices are used without dimmer compatibility, then the circuit design is simpler, but the brightness adjustment capability is lost
Solution Approach 1:
The control circuit is designed to work with both dimmer circuits and direct AC power sources. It detects the presence of a dimmer circuit and automatically adjusts its operation mode accordingly, enabling brightness control when a dimmer is present while maintaining normal operation when connected directly to AC power. This universal compatibility is achieved through intelligent detection and adaptive control strategies.
4Productivity
If current pulses are used to drive LED, then the SMPS can operate with simpler switching control, but the power factor is low and the current is not in phase with voltage
Solution Approach 1:
The control circuit uses periodic pulse-width modulation (PWM) to drive the LED while shaping the input current waveform to be in phase with the input voltage. By synchronizing the switching pulses with the AC voltage cycle and adjusting the pulse width dynamically, the circuit maintains high switching efficiency for LED control while simultaneously achieving high power factor through waveform shaping.
Solution Approach 2:
The control circuit employs feedback mechanisms to monitor both the LED output current and the input current waveform. Based on this feedback, it dynamically adjusts the switching pulses to maintain the desired relationship between input current and voltage phase, ensuring high power factor while preserving the efficiency benefits of pulse-based LED driving.
Data Source
AI summary
A switch mode power supply (SMPS) system includes a rectifying circuit for coupling to an AC input voltage and a transformer having a primary winding for coupling to the rectifying circuit and a secondary winding coupled to the primary winding. The system also has a power switch coupled to the primary winding and a control circuit coupled to the power switch. The control circuit is configured to control current flow in the primary winding such that an envelope waveform formed by peak points of current pulses is in phase with the magnitude of the AC input voltage. Moreover, the SMPS system is configured to provide a constant average output current.