Flyback SMPS Mains Voltage Compensation via Sense Resistor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Switched mode power supplies, particularly flyback SMPS, experience output power variations due to changes in mains input voltage, leading to increased complexity and circuit requirements when attempting to maintain constant power across different voltage levels.
Innovation Solution
The solution involves deriving the mains voltage level from the rate of change of the sense voltage within the existing feedback control system, reusing the current sensing pin to detect mains voltage, and adjusting the maximum current level through the switching element, thereby integrating mains voltage compensation into the feedback loop without additional signal pins or circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the maximum output power increases with increasing mains voltage to meet higher power demands, then the power supply can deliver more power at high mains voltages, but the output power becomes inconsistent across different mains voltage levels
Solution Approach 1:
The patent changes the reference voltage parameter dynamically based on the detected mains voltage level. When high mains voltage is detected (indicating faster current ramp-up), the reference voltage is reduced, which compensates for the increased power delivery and maintains consistent output power across different mains voltage levels.
2Stability of the object's composition
If a separate mains voltage detection circuit is added to compensate for power variations, then the output power consistency can be maintained, but the circuit complexity increases
Solution Approach 1:
The patent makes the existing sense resistor serve multiple functions: it continues to sense the primary current for PWM control while simultaneously enabling mains voltage level detection through its voltage ramp rate. This multi-functionality eliminates the need for separate detection circuits and maintains simple circuit architecture.
Solution Approach 2:
The patent combines the mains voltage detection function with the existing current sensing function by using the same sense resistor and integrating the detection logic into the existing PWM control circuitry. The voltage ramp rate detection is merged with the current feedback mechanism already present in the power supply.
3Stability of the object's composition
If additional signal processing circuits are added to detect mains voltage, then the output power can be maintained constant, but the number of signal connections and processing requirements increases
Solution Approach 1:
The sense resistor voltage itself provides the information needed for both current control and mains voltage detection. The natural voltage ramp created during the switching cycle contains embedded information about the mains voltage level, which the circuit extracts and uses for compensation without requiring external signal sources or additional processing inputs.
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 allows for constant power delivery across varying mains voltage levels without additional signal processing, reducing circuit complexity and enabling over power protection using the same signal for current sensing, thus maintaining consistent output power.
Implementation Method 1
A capacitor is connected across the sense resistor. The voltage change rate signal is converted to a current signal using the capacitor
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A power supply has over power protection based on the same signal as used by the feedback path for controlling the switching of the power supply. This means that no additional signal needs to be supplied to the control circuit to implement mains over protection.