Isolated Forward Converter Control Circuit Using Amplitude Modulated Feedback
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Solution Overview
Problem
Existing isolated DC-to-DC converters face challenges in achieving lossless switching and efficient feedback control due to the isolation barrier between the primary and secondary sides, leading to increased complexity and cost.
Innovation Solution
A control circuit that utilizes an isolation transformer for primary and secondary side isolation, coupled with an error amplifier and isolation driver, allows for amplitude modulation of error signals across the transformer, enabling efficient feedback control with reduced component count and cost by leveraging existing switching signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolation transformer is used to provide primary and secondary side isolation, then safety and prevention of current ground loops are improved, but device complexity and cost increase
Solution Approach 1:
The patent uses the isolation transformer as an intermediary device to transfer the error signal from the secondary side to the primary side while maintaining galvanic isolation. The transformer couples the two sides magnetically without direct electrical connection, thus providing safety isolation while enabling control signal transmission.
Solution Approach 2:
The error signal is amplitude modulated onto a periodic switching waveform at the switching frequency of the converter. This periodic modulation allows the DC error signal to be transmitted through the isolation transformer, which blocks DC but passes AC signals. The periodic nature of the modulation enables reliable signal transmission across the isolation barrier.
2Measurement precision
If feedback control is implemented across the isolation barrier, then output voltage regulation is improved, but device complexity increases due to additional isolation components
Solution Approach 1:
The patent implements a feedback control system where the output voltage on the secondary side is sensed, compared with a reference voltage, and the resulting error signal is transmitted to the primary side through the isolation transformer. The error signal modulates the duty cycle of the primary switch, closing the feedback loop across the isolation barrier to maintain precise output voltage regulation.
Solution Approach 2:
The isolation transformer serves as the intermediary medium that carries the modulated error signal from the secondary side feedback circuit to the primary side control circuit. This allows the feedback function to be implemented without direct electrical connection between sides, maintaining isolation while achieving precise voltage regulation.
3Productivity
If amplitude modulation is used to transmit error signal across isolation transformer, then signal transmission efficiency is improved, but device complexity increases due to modulation circuitry
Solution Approach 1:
The patent leverages the existing switching waveform generated by the converter's own operation as the carrier for amplitude modulation. The error signal modulates this naturally occurring switching waveform, eliminating the need for separate modulation oscillators or carrier signal generators. The converter's switching activity itself provides the modulation carrier.
Solution Approach 2:
The switching waveform serves multiple functions: it drives the power switches for voltage conversion and simultaneously serves as the carrier signal for transmitting the error feedback across the isolation barrier. This multi-functionality reduces the need for separate dedicated modulation circuitry, simplifying the overall design while maintaining efficient signal transmission.
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 solution enables lossless or near-lossless switching and efficient output voltage regulation in isolated DC-to-DC converters, reducing component count and cost while maintaining safety through isolation, thereby addressing the inefficiencies in existing designs.
Implementation Method 1
an isolation transformer operable to transfer the amplitude modulated error signal from the secondary side to the primary side
Data Source
AI summary
An isolated DC-to-DC converter comprises a converter section configured to receive an input voltage and produce an isolated output voltage and a controller section configured to control the operation of the converter section to maintain the output voltage at a predetermined value by, at least in part, turning switches on and off at a certain duty cycle at a set switching frequency. The controller section comprises an isolation transformer providing primary and secondary side isolation and an error amplifier having an output coupled to the isolation transformer, the error amplifier providing an error signal that is representative of the difference between an output voltage and a desired output voltage. The converter further comprises an isolation driver coupled to an isolation driver switch, the isolation driver operable to turn on and off the isolation driver switch at the same frequency as the converter section, the switching of the isolation driver switch resulting in the error signal becoming an amplitude modulated error signal that is transferred across the isolation transformer.