Synchronous Rectifier Control Circuit for Power Converter
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Solution Overview
Problem
Synchronous rectifiers in power converters can accidentally turn on incorrectly, leading to low efficiency in power conversion due to issues with detecting transformer voltages, especially when input voltages are low, causing incorrect measurement of demagnetized times and resulting in resonant ringing errors.
Innovation Solution
A control method and circuit that generate a control signal for synchronous rectification transistors based on the on-time of switching signals, transformer voltages, and output voltages, incorporating protection signals to prevent incorrect turn-on by adjusting the turn-on period of the transistor and using voltage-to-current converters to accurately detect voltages and generate enable and trigger signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectifier is used to achieve high power conversion efficiency, then power conversion efficiency is improved, but incorrect turn-on may occur leading to low efficiency and negative effects
Solution Approach 1:
The control circuit generates the control signal for the synchronous rectification transistor only after the switching signal is turned off, ensuring that the synchronous rectifier cannot turn on during the switching period. This preliminary timing arrangement prevents incorrect turn-on and ensures reliable operation while maintaining high power conversion efficiency.
Solution Approach 2:
The control signal generation is based on feedback from the switching signal status and transformer voltage level. The control circuit continuously monitors these parameters and adjusts the control signal accordingly, preventing incorrect turn-on under various operating conditions including low input voltage scenarios.
2Measurement precision
If control signal is generated based on transformer voltage detection, then synchronous rectification control is improved, but at low input voltages incorrect measurement of demagnetized times occurs causing resonant ringing errors
Solution Approach 1:
The control method incorporates a time threshold parameter that changes based on operating conditions. When the on-time of the switching signal exceeds this threshold, the control signal is generated only after the switching signal turns off. This parameter adjustment ensures accurate demagnetized time measurement even at low input voltages, preventing resonant ringing errors while maintaining precise transformer voltage detection.
3Reliability
If control signal is generated once switching signal is turned off, then incorrect turn-on is prevented, but control response time may be delayed
Solution Approach 1:
The control circuit dynamically adjusts the control signal generation timing based on the switching signal status. By generating the control signal immediately after the switching signal turns off (rather than at a fixed time), the system achieves the fastest possible response while ensuring incorrect turn-on is prevented. This dynamic timing optimization minimizes control delay while maintaining reliability.
Data Source
AI summary
The invention discloses a method for controlling a synchronous rectifier of a power converter and a control circuit using the same. The method includes the following steps. A control signal is generated to control a synchronous rectification transistor in response to an on-time of a switching signal, a level of a transformer voltage and an output voltage of the power converter. The switching signal is used for switching a transformer. The control signal is generated once the switching signal is turned off. A transformer signal is related to an input voltage of the power converter. The control signal is generated when the on-time of the switching signal is longer than a first time threshold.