DCDC Start-Up Control for Transformer Surge Current Suppression
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Solution Overview
Problem
In DCDC circuits, the limited inductance of leakage inductance in transformer-based topologies, such as LLC and DCX circuits, cannot effectively suppress sudden changes in current during start-up, leading to excessive surge currents that can damage switches.
Innovation Solution
A DCDC circuit design that includes a transformer circuit, a synchronous rectification circuit, and a control circuit. The control circuit progressively increases the turn-on duration of switches in both the transformer and synchronous rectification circuits until target voltages are reached, ensuring controlled current entry and suppression of surge currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the leakage inductance of the transformer is used as a resonant inductor to save circuit space and cost, then the circuit structure is simplified and cost is reduced, but the inductance is limited and cannot suppress sudden current changes during start-up
Solution Approach 1:
The patent divides the resonant inductor function into two separate components: the leakage inductance of the transformer and an independent resonant inductor. This segmentation allows each component to have specialized functions - the leakage inductance maintains magnetic coupling while the independent inductor provides sufficient inductance for current suppression during start-up, resolving the contradiction between circuit simplification and current suppression capability.
Solution Approach 2:
The patent introduces an independent resonant inductor as an intermediary component that mediates between the transformer's leakage inductance and the resonant capacitor. This independent inductor acts as a buffer that can handle sudden current changes during start-up, while allowing the leakage inductance to fulfill its primary transformation function, thus protecting switches without compromising circuit efficiency.
2Reliability
If the turn-on duration of switches is increased progressively during start-up, then surge currents are suppressed and switch safety is improved, but the start-up time is extended
Solution Approach 1:
The patent applies preliminary action by implementing a progressive turn-on strategy where the duty cycle of switches is gradually increased from a small initial value during the start-up phase. This preliminary gradual activation allows the circuit to build up voltage and current smoothly before full power operation, preventing surge currents that would otherwise occur during abrupt switch-on, thus protecting switches while establishing stable operation.
Solution Approach 2:
The patent employs dynamics by making the switch turn-on duration variable rather than fixed. During start-up, the duty cycle dynamically increases from a small initial value to the target value over multiple switching cycles. This dynamic adjustment allows the circuit to adapt to different operating conditions - using conservative turn-on durations initially for safety, then transitioning to full performance mode, thereby balancing switch protection with 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
The proposed solution effectively suppresses current surges during the start-up of DCDC circuits, ensuring safe operation and preventing switch damage, while also enabling efficient voltage conversion.
Implementation Method 1
a transformer circuit, a synchronous rectification circuit, and a control circuit
Implementation Method 2
the resonant circuit includes an independent resonant inductor, a resonant capacitor, and a leakage inductance of the transformer
Data Source
AI summary
The present application relates to a DCDC circuit, a circuit start-up method, and an electronic device. The DCDC circuit includes a transformer circuit, a synchronous rectification circuit, and a control circuit; wherein the control circuit is configured to control a turn-on duration of a first switch and a turn-on duration of a second switch in a first bridge circuit of the transformer circuit to increase progressively every switching cycle until an output voltage of the transformer circuit is greater than a first target voltage; and control a turn-on duration of a third switch and a turn-on duration of a fourth switch in a second bridge circuit of the synchronous rectification circuit to increase progressively every switching cycle until an output voltage of the synchronous rectification circuit is greater than a second target voltage.