Multi-channel Switching Regulator Synchronous Rectification Control
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Solution Overview
Problem
In switching regulators, the voltage at the switching terminal can become overvoltage due to a high-impedance state when the transistor for synchronous rectification is turned on after the main switch is turned off, leading to potential circuit loss and reliability issues.
Innovation Solution
A step-up type switching regulator design that includes an inductor and a main transistor in series, with rectification circuits having synchronous rectification transistors disposed in series between output terminals and the switching terminal, where the controlling unit manages the transistors to prevent high impedance at the switching terminal by sequencing their turn-on and turn-off based on a pulse signal, ensuring the switching terminal is coupled with the body diode of the second synchronous rectification transistor during the transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the transistor for synchronous rectification is turned on after the main switch is turned off, then the rectification function is achieved, but the switching terminal enters a high-impedance state causing voltage swings and overvoltage
Solution Approach 1:
The first synchronous rectification transistor is turned on before the main transistor is turned off, in advance preparing a conduction path. This preliminary action ensures that when the main transistor switches off, the switching terminal already has a low-impedance path through the first synchronous rectification transistor, preventing the high-impedance state and voltage swings that would otherwise occur.
2Productivity
If the transistor for synchronous rectification is turned on after the main switch is turned off, then the rectification function is achieved, but the switching voltage exceeds the breakdown voltage affecting reliability
Solution Approach 1:
The first synchronous rectification transistor is activated before the main transistor turns off, pre-establishing a safe voltage path. This prevents the switching voltage from exceeding the breakdown voltage of the second synchronous rectification transistor, thereby protecting the transistor reliability while maintaining rectification efficiency.
Solution Approach 2:
The first synchronous rectification transistor acts as a protective cushion by being turned on in advance. It provides a predetermined low-impedance path that cushions against voltage spikes and overvoltage conditions, preventing damage to the second synchronous rectification transistor and ensuring reliable operation.
3Reliability
If separate control timing is generated for turning on the first synchronous rectification transistor, then precise voltage control is achieved, but control complexity increases
Solution Approach 1:
The control signals for the first and second synchronous rectification transistors are generated by combining their turn-on conditions logically. The first transistor is controlled by a signal that is active when the main transistor is off, while the second transistor is controlled by a signal that is active when both the main transistor is off and a specific timing condition is met. This merging of control logic achieves precise voltage control without requiring entirely separate control timing generation, thereby reducing control complexity.
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 design effectively restrains the rise of switching voltage, reducing overvoltage and maintaining circuit reliability by eliminating the high-impedance period at the switching terminal, and simplifies control by integrating the timing of transistor operations.
Implementation Method 1
the switching terminal and the output terminal are coupled with the body diode of the second synchronous rectification transistor in the period from the time when the first synchronous rectification transistor is turned on to the time when the second synchronous rectification transistor is turned on
Data Source
AI summary
A controlling unit generates a pulse signal whose duty ratio is controlled so that the output voltage of each channel will be constant, and controls the main transistor and the rectification circuit of each channel in accordance with the pulse signal. The first synchronous rectification transistor is disposed in a direction such that the cathode of the body diode thereof is on the switching terminal side. The second synchronous rectification transistor is disposed in a direction such that the cathode of the body diode thereof is on the output terminal side. The controlling unit first turns on the first synchronous rectification transistor, and then turns on the second synchronous rectification transistor for a period of time in accordance with the pulse width of the pulse signal.