Full Bridge LLC Converter ZVS Regulation via Duty Cycle Control
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Solution Overview
Problem
Full bridge LLC converters face challenges in maintaining zero voltage switching (ZVS) during light-load conditions due to increased switching frequency, which can lead to burst mode operation and inefficient output voltage regulation.
Innovation Solution
A switched mode DC-DC power supply with a control circuit that varies the frequency and duty cycle or phase of control signals to the power switches, allowing for wide-range output voltage regulation while maintaining ZVS, by adjusting the duty cycle or phase of only two control signals to minimize switching frequency variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the switching frequency is increased during light-load conditions to regulate output voltage, then the output voltage regulation is improved, but zero voltage switching (ZVS) cannot be maintained and burst mode operation occurs
Solution Approach 1:
The patent changes the control parameter from switching frequency to duty cycle of specific control signals. By varying the duty cycle of only two control signals (while keeping frequency constant), the converter maintains ZVS operation across the full output voltage range while achieving light-load regulation, eliminating the need to increase frequency and avoid burst mode.
2Measurement precision
If the switching frequency is increased above a particular value to regulate output, then output voltage control is achieved, but the converter enters burst mode operation which reduces efficiency
Solution Approach 1:
The invention changes the control approach by varying the duty cycle of select control signals instead of increasing switching frequency. This allows continuous output voltage regulation from 40V to 60V while maintaining efficient continuous conduction mode operation, avoiding the inefficient burst mode that would otherwise occur at light loads.
3Measurement precision
If all control signals are varied to regulate output voltage, then voltage regulation range is improved, but control complexity and impact on output current increases
Solution Approach 1:
The patent applies local quality by varying the duty cycle of only two specific control signals (out of four) to achieve output voltage regulation. This selective control approach simplifies the control system compared to varying all signals, and maintains stable output current by keeping the overall switching frequency constant while achieving wide voltage regulation range.
Data Source
AI summary
A switched mode DC-DC power supply includes a power circuit having an input for receiving an input voltage, an output for providing an output voltage, and four power switches coupled between the input and the output. The four power switches are arranged in a full bridge configuration. The power supply further includes a control circuit coupled to the power circuit for providing a plurality of control signals to the power switches. The plurality of control signals have a variable frequency. The control circuit is adapted to vary the frequency of the plurality of control signals, and to vary a parameter of only two of the plurality of control signals to regulate the output voltage. The parameter is a duty cycle or a phase of said two control signals. Other example switched mode DC-DC power supplies are also disclosed.