Resonant Converter Startup Control for Zero Voltage Switching
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Solution Overview
Problem
Resonant converters, particularly those with half-bridge topology, experience hard switching during the start-up phase, leading to high peak currents and potential transistor destruction due to rapid voltage variations and parasitic SCR triggering.
Innovation Solution
A resonant DC-DC converter with a switching control circuit that temporarily halts the timing circuit after power-on to vary the duty cycle of the square wave voltage during start-up, ensuring the high-side and low-side transistors switch in a Zero Voltage Switching (ZVS) condition by waiting for the current direction to change before activating them.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If resonant converters operate with fixed duty cycle timing circuit during start-up, then the converter can be simplified in control circuitry, but hard switching occurs causing high peak currents and potential transistor destruction
Solution Approach 1:
The patent applies dynamics by making the duty cycle variable during start-up. The control circuit temporarily modifies the timing circuit to vary the duty cycle of the square wave voltage during the start-up phase, allowing the converter to avoid hard switching conditions. After start-up, the duty cycle returns to the normal fixed 50% value. This dynamic adjustment resolves the contradiction by enabling reliable transistor operation during start-up while maintaining simple control circuitry during normal operation.
2Productivity
If the timing circuit operates continuously with 50% duty cycle, then the converter achieves efficient steady-state operation, but hard switching conditions occur during start-up causing shoot-through conditions
Solution Approach 1:
The patent applies preliminary action by preparing the converter for safe start-up before normal operation begins. The control circuit detects when the converter is in start-up mode and temporarily modifies the timing circuit to vary the duty cycle, ensuring that transistors switch under ZVS conditions from the beginning. This preliminary adjustment prevents hard switching and shoot-through conditions during start-up, while allowing efficient 50% duty cycle operation once start-up is complete.
3Speed
If switching elements are activated without waiting for current direction change, then the switching frequency can be maintained, but rapid voltage variations trigger parasitic SCR and cause transistor destruction
Solution Approach 1:
The patent applies feedback by using the resonant current direction as a control signal for the timing circuit. The control circuit monitors the current direction in the resonant circuit and uses this information to determine when to activate the switching elements. By waiting for the current direction to change before activating transistors, the feedback mechanism ensures ZVS conditions are met, preventing parasitic SCR triggering while maintaining the required switching frequency for efficient operation.
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 approach reduces the occurrence of hard switching during start-up, preventing transistor damage and maintaining efficient operation by ensuring both transistors switch with zero drain-to-source voltage, thus avoiding shoot-through conditions.
Implementation Method 1
resonant conversion techniques have been widely developed. These techniques provide for processing electrical power in a sinusoidal manner
Implementation Method 2
This forces the intermediate node shared by the high-side and low-side transistors to fall to ground so that the current flows through the body diode of the low-side transistor
Data Source
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AI summary
A resonant dc-dc converter for converting an input dc voltage to an output dc voltage is provided. The converter includes a switching circuit for receiving the input dc voltage and generating a periodic square wave voltage oscillating between a high value corresponding to the input dc voltage and a low value corresponding to a fixed voltage. The square wave voltage oscillates at a main frequency with a main duty cycle. The converter further includes a switching driving circuit for driving the switching circuit. The switching driving circuit includes a timing circuit for setting the main frequency and the main duty cycle of the square wave voltage. The timing circuit is configured to set the value of the main duty cycle to about 50% when the converter operates in steady state. The converter includes a conversion circuit based on a resonant circuit for generating the output dc voltage from the square wave voltage based on the main frequency and on the main duty cycle. The converter further includes a disabling circuit for temporarily halting the timing circuit after a power on of the converter in such a way to temporarily vary the main duty cycle of the square wave voltage during at least one period of the square wave voltage.