Optocoupler Mains Voltage Detection for Isolated Power Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing supply voltage detection devices lack accurate and reliable methods for determining mains voltage with galvanic isolation, and are influenced by load variations and the need for electrolytic capacitors for smoothing, which can lead to inaccurate measurements and high ripple.
Innovation Solution
The use of an optocoupler to transmit a signal with a duty cycle dependent on the mains voltage value, eliminating the need for capacitors and providing galvanic isolation, allowing for digital conversion and precise detection of the mains voltage, with a zener diode device setting a limit voltage value and a current-limiting resistor to manage excessive currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrolytic capacitors are used to smooth the rectified mains voltage, then the voltage ripple is reduced, but the device complexity increases and the measurement accuracy is compromised due to load influence
Solution Approach 1:
The patent extracts and eliminates the electrolytic capacitors from the voltage smoothing circuit. Instead of using capacitors to smooth the rectified voltage, the invention directly processes the pulsating DC voltage from the rectifier through the optocoupler, removing the problematic component that caused measurement inaccuracies and increased device complexity.
Solution Approach 2:
The patent replaces the passive electronic smoothing circuit (capacitors) with an active digital processing system. The microcontroller measures the duty cycle of the optocoupler output signal and calculates the RMS voltage digitally, substituting the mechanical/electrical smoothing approach with a computational method that achieves higher accuracy without additional passive components.
2Reliability
If a transformer is added to provide galvanic isolation, then the isolation is achieved, but the device complexity increases and the voltage measurement becomes less accurate due to high fluctuation with small load variations
Solution Approach 1:
The patent introduces an optocoupler as an intermediary device between the mains voltage circuit and the control electronics. The optocoupler provides galvanic isolation through optical coupling while maintaining a direct relationship between the input voltage and output signal duty cycle, eliminating the measurement errors introduced by transformer load variations.
Solution Approach 2:
The patent changes the parameter being measured from the instantaneous voltage (which fluctuates with load) to the duty cycle of the optocoupler output signal. By measuring how long the optocoupler conducts during each AC cycle rather than the voltage level itself, the system achieves accurate RMS voltage measurement that is immune to load-induced fluctuations.
3Stability of the object's composition
If the voltage is smoothed with capacitors, then the DC voltage is stabilized, but the device requires additional components and the response speed is reduced
Solution Approach 1:
The patent employs periodic action by utilizing the natural frequency of the AC mains voltage. The optocoupler is triggered at each zero-crossing and conducts during the positive half-cycle, creating a periodic signal whose duty cycle directly reflects the RMS voltage. This approach achieves voltage stabilization through rhythmic, predictable switching rather than passive energy storage.
Solution Approach 2:
The patent maintains continuous useful action by processing every AC cycle without interruption. The microcontroller continuously measures the optocoupler duty cycle and updates the voltage reading in real-time, eliminating the delay inherent in capacitor charging/discharging cycles and achieving both stability and fast response.
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 accuracy and speed of mains voltage detection, enabling quick and precise switching between mains and emergency power supplies, while maintaining stability over a wide temperature range without the need for electrolytic capacitors.
Implementation Method 1
a signal can be transmitted by the optocoupler for the duration of this exceeding, with a duty cycle dependent on the mains voltage value being able to be determined from the signal duration and period of the signal
Implementation Method 2
a zener diode device (6) with at least one zener diode (7) is connected between the rectifier (5) and the optocoupler (4)
Implementation Method 3
a rectifier (5) connected to the mains voltage supply (2)
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to a supply voltage detection device (1), particularly for at least one load, for monitoring a rectified mains voltage of a mains voltage supply (2) and comparing a detected mains voltage value to a predetermined reference value; if this detected mains voltage value is lower than the reference value, using an electronic control system (3) it is possible to switch to, for example, an emergency voltage of an emergency voltage supply. In addition, the rectified mains voltage can be fed to an optocoupler (4) if a voltage limit value has been exceeded, and a signal can be transmitted from said optocoupler for the duration of this excess, it being possible to determine a duty cycle that is dependent on the mains voltage value, from the duration and period of this signal.