Adaptive Synchronous Rectifier Control for Low Voltage DC-DC Converters
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Solution Overview
Problem
Low power electronic circuits face efficiency degradation due to voltage drop and power loss in output rectifier diodes, particularly in low voltage applications, where existing solutions require expensive components or complex signaling schemes to achieve high efficiency in DC-DC converters.
Innovation Solution
A current loop powered DC-DC converter with a switch transformer and active rectifier using an adaptive control scheme, where a phase detector and charge pump regulate the pulse length of the gate drive signal for the FET transistor, synchronizing it with the transformer secondary signal to minimize power loss and improve efficiency without needing additional transformer windings or complex signaling across the isolation barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an active rectifier using FET transistor is employed to reduce power loss, then converter efficiency is improved, but device complexity and cost increase due to expensive electronic components or complex signaling schemes
Solution Approach 1:
The synchronous rectifier circuit drives itself using the transformer secondary voltage to control the FET switching, eliminating the need for external control signals across the isolation barrier. The circuit automatically synchronizes with the transformer voltage, providing self-driven operation that reduces both complexity and cost while maintaining low power loss
Solution Approach 2:
A delay circuit is introduced as an intermediary element between the transformer secondary voltage and the FET gate drive signal. This delay circuit introduces a controlled time delay to ensure proper timing of the FET switching relative to the transformer voltage waveform, enabling simple autonomous control without complex signaling schemes
2Loss of energy
If complex dual structure phase-lock loops and voltage controlled oscillators are used for synchronous rectification, then rectifier efficiency is improved, but device complexity increases significantly
Solution Approach 1:
The invention extracts only the essential timing control function needed for synchronous rectification, removing unnecessary components such as voltage controlled oscillators and complex phase-lock loop structures. By using only a simple delay circuit to provide the required timing delay, the solution achieves synchronous rectification with minimal complexity
Solution Approach 2:
Instead of using complex phase-lock loops to generate control signals, the invention inverts the approach by using the transformer secondary voltage itself as the control reference and introducing a simple delay to generate the FET gate drive signal. This reversal of the control signal generation approach dramatically simplifies the circuit while maintaining rectifier efficiency
3Difficulty of detecting and measuring
If current sensing by voltage sense across switching element is used, then switching state detection is achieved, but continuous power dissipation occurs reducing converter efficiency
Solution Approach 1:
The invention uses periodic sampling of the transformer secondary voltage to detect switching states and control FET timing, rather than continuous voltage sensing across the switching element. This periodic action approach achieves accurate switching state detection while minimizing power dissipation by sensing only when needed
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
The solution achieves high efficiency in low voltage and low power applications, such as current loop transmitters, by minimizing power loss and maintaining reliability under varying conditions using readily available standard electronic components, thus meeting the stringent power budget requirements of devices like temperature transmitters.
Implementation Method 1
a phase detector driving a charge pump and a loop filter, which charge pump and loop filter generates a control signal to control the pulse length driving the switch element
Implementation Method 2
a phase detector driving a charge pump and a loop filter, which charge pump and loop filter generates a control signal
Implementation Method 3
the active rectifier is comprised of a field-effect transistor, FET transistor, and an adaptive control circuit driving the FET transistor
Implementation Method 4
a switching transformer having a primary and a secondary winding, the primary winding being connected to a drive circuitry and the secondary winding being connected to at least one active rectifier
Data Source
AI summary
The present invention relates to a current loop powered DC-DC switch mode converter for use as a local isolated low power supply for electronic circuits such as current loop transmitters where the requirements for supply efficiency and cost of the implementation is critical. It is the object of the invention to provide a simple and low cost solution for driving a synchronous rectifier thereby improving the supply efficiency, especially at low output voltages.