Monolithic Isolator Circuit Using Z-Domain Feedback
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Solution Overview
Problem
Existing isolated systems, such as AC/DC and DC/DC converters, face reliability issues and bandwidth limitations due to the use of optocouplers, which tend to wear out and are prone to limit cycle oscillations, and existing alternatives like RF and magnetically coupled systems are either expensive or restricted to AC only applications.
Innovation Solution
A monolithic isolator circuit utilizing z-domain differential delay lines and digital compensators to create an error feedback structure, allowing for high bandwidth communication of analog information across an isolation barrier, replacing standard optocoupler feedback configurations and enabling cycle-by-cycle loop control and protection functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optocouplers are used for isolation feedback, then isolation functionality is achieved, but reliability deteriorates due to wear out
Solution Approach 1:
The patent replaces the optical-mechanical optocoupler system with a magnetic field-based isolation feedback system. The primary side feedback controller uses a feedback transformer and auxiliary winding to generate feedback signals, while the secondary side uses a current transformer to sense output current. This magnetic coupling mechanism eliminates the mechanical/optical components that wear out, providing indefinite operational life while maintaining isolation functionality.
2Speed
If optocouplers are used for isolation feedback, then isolation functionality is achieved, but bandwidth is limited
Solution Approach 1:
The patent substitutes the bandwidth-limited optocoupler with a magnetic field-based feedback system that achieves wider bandwidth through direct magnetic coupling. The feedback transformer and current transformer provide low-impedance magnetic coupling paths that extend the usable frequency range compared to optical coupling, while the solid-state magnetic components maintain higher reliability.
3Reliability
If primary side feedback is used to eliminate optocouplers, then reliability improves, but accuracy deteriorates
Solution Approach 1:
The patent divides the feedback function into two separate magnetic coupling paths: a feedback transformer for voltage feedback and a current transformer for current sensing. This segmentation allows each path to be optimized for its specific function, improving overall accuracy while maintaining the reliability benefits of eliminating optocouplers. The auxiliary winding on the feedback transformer provides additional sensing capability for enhanced precision.
4Reliability
If RF isolators are used for isolation, then isolation functionality is achieved, but cost and power consumption increase
Solution Approach 1:
The patent operates the magnetic feedback system at lower frequencies compared to RF isolators, typically in the audio to low-frequency range suitable for power converter feedback. This parameter change allows the use of simpler, lower-cost magnetic components and reduces power consumption while maintaining adequate isolation performance for the application requirements.
5Ease of manufacture
If magnetically coupled systems are used for isolation, then cost is reduced, but application scope is limited to AC only
Solution Approach 1:
The patent implements a dynamic feedback control system that can adapt to both AC and DC operating conditions. The primary side feedback controller continuously monitors and adjusts the feedback signals based on real-time operating conditions, enabling the system to maintain accurate regulation across varying load conditions, input voltages, and both AC and DC applications, thus expanding versatility beyond static magnetic coupling limitations.
Data Source
AI summary
A monolithic isolator circuit is provided which replaces optocoupler feedback configurations which are prone to wear out, lack reliability, and bandwidth limitations. By communicating only a subset of a sigma delta modulators quantizer across the isolator but closing the modulator loop on the primary side, much wider bandwidth communications of analog information can be achieved than with optocouplers. This allows for the use of the proposed isolator for cycle by cycle loop control and protection functions which previously required components on the local side of the isolation. The monolithic isolator circuit can be extended to isolate analog to digital converters (ADC), analog buffers, and to isolated current sense amplifiers (CSA). The monolithic isolator circuit utilizes a z-domain differential delay line to create an error in conformance with the difference between the feedback magnitude and a reference. Z-domain differential delay lines have a fast response, and may be windowed and event driven making these delay lines very current efficient. The conformance error may be fed to a digital compensator (such as a proportional-integral-derivative (PID) compensator) and finally to a z-domain modulator. The z-domain modulator may be one of several constructions, however, to achieve a reasonable number of bits a delta sigma structure, such as an error feedback structure, is utilized for the modulator.