Switch Mode Power Supply High Power Factor Control Without Line Voltage Sampling
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Solution Overview
Problem
Conventional switched mode power supplies for LED lighting systems suffer from inefficiencies in AC power utilization, measured by power factor, and are prone to noise and instability due to line voltage sampling.
Innovation Solution
A switch mode power supply with a power switch having a constant turn-on time in each cycle of rectified input line voltage, where the maximum value of peak currents is compared to a reference signal to adjust the turn-on time, maintaining the output in phase with the line voltage without line voltage sampling, using a controller chip with as few as five pins or seven pins with external resistors for mode selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional LED light bulbs are used, then they can provide lighting function, but they do not provide desirable efficiency in AC power utilization (low power factor)
Solution Approach 1:
The patent employs periodic action by operating the power supply in cycles synchronized with the rectified AC line voltage. The controller adjusts the power switch turn-on time periodically, with each cycle corresponding to one period of the rectified input voltage, ensuring the output current envelope follows the input voltage waveform to achieve high power factor
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the power switch turn-on time based on the comparison between the maximum peak current and reference signal. This parameter adjustment ensures the output current waveform maintains proper phase relationship with input voltage, improving power factor without energy loss
2Loss of energy
If line voltage sampling is used to improve power factor, then power factor can be improved, but the circuit becomes complicated and performance becomes susceptible to noise and instability
Solution Approach 1:
The patent extracts and eliminates the line voltage sampling function from the circuit. Instead of sampling the noisy line voltage, the controller generates control signals based solely on the rectified input voltage and internal reference signals, removing the source of noise and instability while maintaining power factor correction
Solution Approach 2:
The patent introduces an intermediary approach by using the rectified input voltage itself as the basis for control, rather than sampling the original line voltage. The controller uses this rectified voltage along with internal reference signals to generate the power switch control signals, creating a stable intermediate control mechanism that avoids noise
3Loss of energy
If line voltage sampling is used to improve power factor, then power factor can be improved, but the system becomes susceptible to noise and instability
Solution Approach 1:
The patent removes the vulnerable line voltage sampling function from the system. By eliminating this sampling mechanism, the system no longer suffers from noise and instability issues associated with sampling the noisy AC line voltage, while maintaining power factor correction through alternative control methods
Solution Approach 2:
The system serves itself by using internally generated reference signals and the rectified input voltage to control the power switch. This self-service approach eliminates dependence on external line voltage sampling, making the system inherently more reliable and resistant to noise and instability
Data Source
AI summary
An SMPS received a rectified periodic input line voltage and is configure to provide a regulated output. A power switch has a constant turn-on time in a given cycle of the rectified periodic input line voltage. A maximum value of the envelope of peak currents through the power switch is determined and is compared with a reference value, and the power switch turn-on time in the next cycle is adjusted accordingly. The output of the power supply is regulated to a target output value, and the current is in phase with the periodic input line voltage, resulting in a high power factor. No sampling of the line voltage is needed to maintain the high power factor. A controller chip can have as few as five pins. Alternatively, a seven-pin controller chip can have two external resistors for selecting operations in either Boundary Conduction Mode (BCM) or Discontinuous Conduction Mode (DCM).