Isolated Power Converter PWM Voltage Sensing Across the Barrier
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Solution Overview
Problem
Current isolated power converters face challenges in accurately transferring output voltage information across the isolation barrier due to the non-proportional relationship between the error voltage and the output voltage, limiting precise voltage regulation.
Innovation Solution
A control circuit that uses a PWM signal with a duty cycle proportional to the output voltage, transferred across the isolation barrier, and filtered to produce a control signal for regulating the output voltage, along with a microcontroller that determines the output voltage value and calibrates the gain for precise voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an optocoupler is used to transfer the error voltage across the isolation barrier, then electrical isolation between input and output sides is maintained, but the error voltage is not directly proportional to the output voltage, limiting measurement precision
Solution Approach 1:
The patent introduces a PWM signal as an intermediary carrier to transfer output voltage information across the isolation barrier. Instead of directly transferring the error voltage through the optocoupler, the system converts the output voltage into a PWM signal with duty cycle proportional to the voltage, transfers it through the optocoupler, and then recovers the voltage information on the primary side. This intermediary approach maintains electrical isolation while enabling accurate voltage measurement.
Solution Approach 2:
The patent changes the parameter being transferred from error voltage to PWM duty cycle. By converting the output voltage information into a time-based PWM signal parameter rather than directly transferring voltage, the system achieves both electrical isolation and direct proportionality between the transferred signal and output voltage, resolving the measurement precision issue.
2Measurement precision
If a PWM signal with duty cycle proportional to output voltage is transferred across the isolation barrier, then direct proportionality between control signal and output voltage is achieved, but additional circuit components and processing steps are required
Solution Approach 1:
The patent makes the optocoupler perform multiple functions: it not only provides electrical isolation but also serves as the transfer medium for the PWM signal that carries the voltage information. The PWM generation circuit and filtering circuit work together to convert voltage to PWM and back, creating a universal signal transfer mechanism that handles both isolation and measurement tasks.
3Loss of time
If the error voltage is transferred directly across the isolation barrier, then the circuit structure is simple, but the response time and regulation accuracy are limited due to the non-proportional relationship
Solution Approach 1:
The patent employs periodic PWM signals to transfer the voltage information. By using pulse-width modulation with a defined frequency, the system creates a periodic signal that efficiently carries the voltage information across the isolation barrier. This periodic approach enables faster response compared to direct voltage transfer, as the PWM frequency can be optimized for rapid information transmission while maintaining accuracy.
Data Source
AI summary
A control circuit for an isolated power converter includes a first sensing circuit that senses a secondary side output voltage and produces a pulse width modulation (PWM) signal having a duty cycle that is proportional to a value of the secondary side output voltage. The PWM is transferred a cross the converter isolation barrier to the primary side, and a primary side circuit receives the PWM signal and outputs a control signal. A controller determines the value of the secondary side output voltage from the control signal and uses the value to control primary side power switching devices of the isolated power converter to regulate the secondary side output voltage at a selected value.