Half-Bridge Converter Startup Duty Cycle Control
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Solution Overview
Problem
Half-bridge dc-dc converters experience high switching losses and hard switching conditions during startup due to asymmetrical magnetic flux and rapid current transitions, leading to inefficiencies and potential parasitic SCR triggering.
Innovation Solution
A half-bridge switching dc-dc converter with a switching control circuit that dynamically varies the duty cycle of the control signals during startup, ensuring the high-side transistor switches in a Zero Voltage Switching (ZVS) condition by maintaining a guard interval and adjusting the duty cycle to prevent hard switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the switching frequency is increased to reduce transformer size, then the transformer and filter sizes are reduced, but the switching losses and driving losses increase proportionally
Solution Approach 1:
The patent changes the switching parameters dynamically by implementing different duty cycles during startup versus normal operation. During startup, a first duty cycle is used that prevents hard switching, while during normal operation, a second duty cycle enables higher frequency switching with reduced component size. This parameter change resolves the contradiction by optimizing for different operational phases.
2Device complexity
If hard switching is used to simplify the switching control, then the control circuit is simpler, but the switching losses increase particularly during startup
Solution Approach 1:
The patent implements dynamic control by varying the duty cycle based on the operational phase. The control circuit dynamically adjusts between a first duty cycle during startup that avoids hard switching and a second duty cycle during normal operation. This dynamic approach maintains relatively simple control circuitry while significantly reducing switching losses during the critical startup phase.
3Productivity
If the duty cycle is fixed at 50% for symmetric operation, then the converter operates efficiently in steady state, but hard switching occurs during startup due to asymmetrical magnetic flux
Solution Approach 1:
The patent applies preliminary action by using a specific first duty cycle during the startup phase that prevents hard switching before the converter reaches steady state. This preliminary duty cycle configuration ensures that the magnetic flux builds up symmetrically from the beginning, preventing the asymmetrical flux conditions that would otherwise cause hard switching. Once startup is complete, the duty cycle transitions to the standard 50% for efficient steady-state 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
The solution reduces switching losses and prevents hard switching during startup, improving efficiency and reducing power wastage by ensuring symmetrical current sourcing and sinking, thus maintaining converter stability and extending component lifespan.
Implementation Method 1
A switching circuit is provided with a high-side switching element and a low-side switching element connected in series between an input terminal for receiving an input dc voltage and an output terminal for providing a converted output voltage
Implementation Method 2
An input resonant network is provided coupled with a primary winding of a transformer, in such a way that a network formed by the input resonant network and the primary winding of the transformer acts as a resonant tank
Data Source
AI summary
A half bridge switching dc-dc converter an input dc voltage to an output dc voltage. The converter includes a switching circuit for receiving the input dc voltage and generating a periodic square wave voltage oscillating from a high value corresponding to the input dc voltage to a low value corresponding to a reference voltage. The periodic square wave voltage oscillates at a main frequency with a main duty cycle equal to about 50% when the converter operates in a steady state. The converter further includes a conversion circuit for providing the output dc voltage from the square wave voltage based on the main frequency and on the main duty cycle. The converter still further comprises a switching control circuit controlling the switching circuit for temporarily varying the main duty cycle during at least one period of the square wave after a power on of the converter.