Switching Power Supply Zero Current Detection Timing Control
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Solution Overview
Problem
Conventional switching power supplies face challenges in accurately measuring the voltage across the active switch without delay, leading to increased equipment costs and energy losses due to inappropriate correction of the freewheeling switch's on time, which results in unwanted inductor current flow from the output to the input.
Innovation Solution
A switching power supply that incorporates a zero current detector, a controller for on/off control, and a voltage meter to calculate and adjust the second on period of the synchronous rectifier, avoiding direct measurement of the switch voltage, thereby correcting the on time of the freewheeling switch and preventing negative inductor current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the voltage across the active switch is measured accurately without delay, then the on time correction of the freewheeling switch is improved, but the equipment cost increases due to requiring dedicated controllers with high withstand voltage
Solution Approach 1:
The patent introduces an intermediary approach by measuring the voltage across the boost inductor instead of directly measuring the switch voltage. This indirect measurement method uses a voltage divider circuit that can be implemented with standard components, avoiding the need for expensive dedicated controllers with high withstand voltage capabilities. The inductor voltage measurement serves as a mediator to infer the switch voltage state without direct exposure to high voltage stress.
Solution Approach 2:
The patent employs inexpensive voltage division circuits and standard microcontroller units rather than costly dedicated high-voltage controllers. By using affordable components like resistors for voltage division and conventional MCUs for processing, the system achieves accurate voltage measurement and timing control without the high equipment cost associated with specialized high-voltage controllers.
2Measurement precision
If the freewheeling switch is kept on after the inductor current starts flowing backward to release charge, then the voltage measurement accuracy is improved, but the energy loss increases due to unwanted backward current flow
Solution Approach 1:
The patent implements feedback control by continuously monitoring the inductor current direction and the inductor voltage, and adjusting the freewheeling switch timing accordingly. The controller detects when the inductor current reverses direction and uses this feedback information to terminate the freewheeling switch's on state at the optimal moment, preventing excessive backward current flow while ensuring complete charge release. This closed-loop feedback mechanism balances measurement accuracy requirements with energy efficiency.
Solution Approach 2:
The patent employs dynamic timing adjustment for the freewheeling switch based on real-time operating conditions. Rather than using a fixed on-time, the controller dynamically modifies the switch's conduction period according to the instantaneous inductor current direction and voltage state. This dynamic control allows the system to adapt the switch timing to match the actual energy release requirements, minimizing unnecessary backward current and associated energy losses.
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 solution allows for accurate correction of the freewheeling switch's on time without measuring the switch voltage, reducing equipment costs and minimizing energy losses by ensuring the synchronous rectifier is switched off before the inductor current becomes zero, thus preventing unwanted current flow.
Implementation Method 1
a detection winding, which is magnetically coupled to the boost inductor and outputs a zero current detection signal
Data Source
AI summary
A switching power supply includes a power converter with an inductor and first and second switches that converts a voltage Vac to a voltage Vdc, a detector with a winding that detects zero timing of an inductor current, and a driving signal generator that switches on the second switch based on the zero timing and then switches on the first switch. The driving signal generator ends a period T2 before the zero timing by executing a measuring process for an on period T1 of the second switch, a process that calculates the period T2 from T2=T1×|Vac|/(Vdc−|Vac|)−Tc using a correction time Tc, a process that switches on the first switch for only the period T2, a process that measures an elapsed time between the periods T2 and T1, and a process that changes the correction time Tc so that the elapsed time becomes a target time.