Optocoupler Isolation Circuit With Gain-Error Compensation
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Solution Overview
Problem
Switched mode power supplies using optocouplers for isolated data transfer suffer from significant gain deviation, leading to reproducibility issues and high costs due to the need for factory calibration to compensate for gain errors.
Innovation Solution
A circuit design that translates sensed signals into time-sequential first and second current levels using a conversion circuit and optocoupler, combined with an analog-to-digital converter and controller, to derive the original signal independently of the optocoupler's gain, allowing the use of optocouplers with higher gain deviation without accuracy loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an optocoupler is used for isolated data transfer, then galvanic isolation is achieved, but gain deviation reaches up to 200% causing large measurement errors
Solution Approach 1:
The patent applies periodic action by using time-sequential switching between two reference voltages (Vref and 2*Vref) to generate two distinct current levels. This periodic switching allows the system to transfer not only the sensor signal but also reference information through the optocoupler, enabling gain compensation without requiring high-precision optocouplers.
Solution Approach 2:
The patent changes the voltage parameter dynamically by switching between two different reference voltage levels (Vref and 2*Vref) based on the sensor signal state. This parameter change creates two distinguishable current levels at the optocoupler output, allowing the receiving end to determine the original signal state while compensating for optocoupler gain variations through ratio calculation.
2Measurement precision
If expensive optocouplers with lower gain deviation are used, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent uses inexpensive optocouplers with high gain deviation by compensating for their imperfections through a clever circuit design. Instead of relying on the optocoupler's inherent precision, the system uses time-sequential voltage switching and ratio calculation to achieve accurate signal transfer, effectively making the optocoupler's gain characteristic irrelevant to the final measurement accuracy.
Solution Approach 2:
The patent creates a reference copy of the signal path by introducing two known reference voltage levels (Vref and 2*Vref) that are switched sequentially. This reference copying allows the system to measure and compensate for the optocoupler's actual gain in real-time, replacing the need for expensive precision optocouplers with a combination of cheaper components and intelligent processing.
3Measurement precision
If factory calibration is performed to compensate for gain error, then measurement precision is improved, but productivity decreases due to time-consuming calibration process
Solution Approach 1:
The patent implements self-service by enabling the system to automatically compensate for optocoupler gain variations during normal operation without requiring external calibration equipment or procedures. The time-sequential voltage switching and ratio calculation method allows the system to self-correct for gain errors dynamically, eliminating the need for time-consuming factory calibration processes.
Solution Approach 2:
The patent performs preliminary action by pre-establishing two known reference voltage levels (Vref and 2*Vref) that are switched sequentially before the actual measurement. This preliminary voltage switching creates a reference framework that enables immediate gain compensation when the signal is received, eliminating the need for separate calibration steps and allowing production to proceed without delays.
4Measurement precision
If time-sequential voltage levels are used with reference voltage combination, then measurement precision is improved by filtering out gain error, but device complexity increases
Solution Approach 1:
The patent uses periodic action through time-sequential switching of reference voltages to encode the sensor signal into two distinct current levels. This periodic voltage switching, combined with the optocoupler's natural current transfer characteristic, creates a self-referencing measurement system that inherently compensates for gain variations without requiring complex additional compensation circuits.
Solution Approach 2:
The patent achieves gain error immunity through parameter changes by dynamically switching between two reference voltage levels (Vref and 2*Vref) based on the sensor signal. This parameter switching creates a differential measurement approach where the ratio of the two voltage levels remains constant even when the optocoupler's absolute gain varies, effectively filtering out gain errors through mathematical relationship rather than complex circuitry.
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
Enables accurate and cost-effective isolated data transfer by eliminating the impact of optocoupler gain deviation, facilitating the use of cheaper components while maintaining high precision.
Implementation Method 1
A common way of providing galvanically isolated data transfer is to use an optocoupler
Data Source
AI summary
The invention relates to a circuit for providing isolated data transfer. The circuit comprises a sensor adapted to be coupled to a conversion circuit, the conversion circuit, which is adapted to use a signal generated by the sensor and an offset voltage to generate in a time sequential manner, a first voltage level and a second voltage level, wherein the second voltage level is larger than the first voltage level. The circuit comprises a voltage to current transformer circuit adapted to convert the first voltage level into a first current level within a current range and the second voltage level into a second current level within the current range, wherein the first current level and the second current level are time sequentially provided to an optocoupler. The optocoupler is adapted to receive time sequentially the first current level and the second current level and to provide an isolated output voltage having a first voltage when the first current level is provided to the optocoupler and a second voltage when the second current level is provided to the optocoupler, an analog to digital converter adapted to receive the isolated output voltage and adapted to provide a digital output voltage and a controller coupled to the analog to digital converter, wherein the controller is adapted to derive the signal generated by the sensor from the digital output voltage corresponding to the isolated output voltage received in the time sequential manner.