Switching Power Supply Dead Time Control for ZVS
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Solution Overview
Problem
Switching power supplies using the phase shift method face efficiency issues in discontinuous current mode due to insufficient dead time, leading to reduced conversion efficiency as the resonance completion period is not long enough to handle the sharp increase in dead time.
Innovation Solution
A control circuit that determines the current mode by comparing measured and theoretical phase shift values, prolonging dead time in the full-bridge circuit when operating in discontinuous current mode to ensure zero voltage switching (ZVS) and maintain conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dead time is prolonged to ensure resonance completion in discontinuous current mode, then zero voltage switching (ZVS) can be established, but the conversion efficiency decreases due to increased switching loss and extended dead time
Solution Approach 1:
The patent implements dynamic dead time adjustment by detecting the current mode (continuous or discontinuous) and modifying the dead time parameter accordingly. The control circuit monitors the resonance completion status and adapts the dead time duration to match the actual operating conditions, ensuring ZVS is achieved without excessive energy loss.
Solution Approach 2:
The patent changes the dead time parameter based on the detected current mode and resonance completion status. By adjusting this critical timing parameter dynamically, the system optimizes the balance between achieving ZVS (which requires sufficient dead time) and minimizing switching losses (which are increased by prolonged dead time).
2Reliability
If the dead time is continuously prolonged in accordance with output current decrease, then resonance completion is attempted, but the prolonged dead time is insufficient to handle the sharp increase in required dead time in discontinuous current mode
Solution Approach 1:
The patent employs feedback mechanisms where the control circuit monitors the actual resonance completion status and compares it with the theoretical expectation. Based on this feedback, the system detects when it operates in discontinuous current mode and adjusts the dead time accordingly, ensuring sufficient time for resonance completion without relying on continuous prolongation alone.
Solution Approach 2:
The patent performs preliminary detection of the current mode and resonance completion status before finalizing the dead time setting. By anticipating the need for extended dead time in discontinuous mode through advance detection, the system can prepare and apply the appropriate dead time duration, preventing the insufficiency that occurs with merely continuous prolongation.
3Ease of operation
If the resonance completion period is calculated based on resonant circuit characteristics and output current, then dead time can be set theoretically, but the calculated period is not long enough to handle the sharp increase in dead time in discontinuous current mode
Solution Approach 1:
The patent enables the control circuit to automatically detect the current mode and resonance completion status, and self-adjust the dead time parameter without external intervention. The system uses its own operational parameters (output current, voltage, timing) to determine when discontinuous mode occurs and accordingly extends the dead time beyond the theoretical calculation to ensure adequacy.
Solution Approach 2:
The patent transitions from a static theoretical dead time calculation to a dynamic adjustment mechanism. The dead time is no longer fixed based solely on theoretical calculations but is continuously adapted based on the detected operating mode and resonance completion status, ensuring adequacy in both continuous and discontinuous current modes.
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 effectively sets appropriate dead time in discontinuous current mode, suppressing the decrease in conversion efficiency and ensuring efficient operation by determining the current mode and adjusting dead time accordingly.
Implementation Method 1
a resonant coil is provided between the full-bridge circuit and the insulated transformer, and the capacitance component of the switching elements provided in the full-bridge circuit and the inductance component of the resonant coil form a resonant circuit
Implementation Method 2
supplies the AC voltage via an insulated transformer to an output circuit
Data Source
AI summary
A switching power supply includes an insulated transformer, a full-bridge circuit which converts input DC power into AC power and outputs the AC power to a primary-side coil, an output circuit which converts AC power input from secondary-side coils into DC power and outputs the DC power, and a control circuit which controls the full-bridge circuit by using a phase shift method based on voltage output by the output circuit. When a measured value of the amount of phase shift determined from at least one of the voltage and current output by the output circuit is smaller than a theoretical value of the amount of phase shift corresponding to the switching power supply operating in a continuous current mode, the control circuit prolongs dead time used in the full-bridge circuit in accordance with the difference between the measured value and the theoretical value.