SMPS Power Factor Correction via Zero-Crossing Switch Control
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Solution Overview
Problem
Conventional switching mode power supplies (SMPS) fail to provide a desirable power factor, leading to inefficiencies and inability to meet energy standards, particularly in LED backlight drivers where they result in low power factor and high harmonic components.
Innovation Solution
The SMPS incorporates a control circuit that manages a power switch to discharge the input capacitor during AC voltage zero crossings and prevent discharging during peak or valley phases, ensuring a larger conduction angle and improved power factor by aligning the input AC current with the AC voltage waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional rectifier circuit is used in SMPS, then the circuit structure is simple, but the power factor is low and harmonic components are high
Solution Approach 1:
The control circuit predicts the zero-crossing point of the AC input voltage in advance and triggers the power switch to turn on before the zero-crossing point. This preliminary action allows the rectifier to start conducting earlier in the AC cycle, extending the conduction angle and improving the power factor without adding complex circuit structures.
Solution Approach 2:
The invention dynamically adjusts the turn-on timing of the power switch based on the detected AC voltage waveform characteristics. By continuously monitoring the AC input and adaptively controlling the switch timing, the system optimizes the conduction angle in real-time, thereby improving power factor while maintaining simple circuit architecture.
2Device complexity
If power switch is turned on at conventional timing, then the control is simple, but the conduction angle is limited and power factor is low
Solution Approach 1:
The control circuit predicts the zero-crossing point of the AC input voltage in advance and triggers the power switch to turn on before the zero-crossing point. This preliminary action allows the rectifier to start conducting earlier in the AC cycle, extending the conduction angle and improving the power factor without adding complex circuit structures.
Solution Approach 2:
The control circuit continuously detects the AC input voltage waveform and uses this feedback information to dynamically adjust the power switch turn-on timing. This closed-loop control ensures optimal conduction angle by adapting to variations in the AC waveform while keeping the control logic relatively simple.
3Duration of action of stationary object
If input capacitor discharges continuously, then the power delivery is continuous, but the harmonic components increase and power factor decreases
Solution Approach 1:
The invention implements periodic control of the input capacitor discharge by synchronizing the power switch operation with the AC input voltage cycles. The switch is turned on near each zero-crossing point and off near peak/valley points, creating a periodic discharge pattern that follows the AC waveform. This periodic action reduces harmonic components by aligning the discharge current with the voltage waveform, thereby improving power factor while maintaining continuous power delivery over the full cycle.
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 the power factor of SMPS systems, reducing harmonic components and meeting or exceeding energy standards by providing a more efficient power delivery, suitable for LED drivers and other applications.
Implementation Method 1
a rectifying device configured for converting a periodically varying input AC (alternating current) voltage into a DC (direct current) voltage
Implementation Method 2
An input capacitor having a first terminal coupled to the rectifying device and the primary winding of the transformer
Implementation Method 3
a transformer including a primary winding, a secondary winding, and an auxiliary winding. The primary winding is coupled to the rectifying device
Data Source
AI summary
A switching mode power supply (SMPS) includes a rectifying device configured for converting a periodically varying input AC (alternating current) voltage into a DC (direct current) voltage, and a transformer including a primary winding, a secondary winding, and an auxiliary winding. The primary winding is coupled to the rectifying device. An input capacitor is coupled to the rectifying device and the primary winding of the transformer. A first power switch is coupled to the input capacitor. A control circuit is coupled to the first power switch and is configured to control the first power switch based on a phase or amplitude of the input AC voltage. By controlling the charging and discharging of the input capacitor, power is provided to the primary winding during a longer portion of the AC input voltage cycle, allowing the rectifier device to have a larger conduction angle to increase a power factor (PF).