DC-to-DC Controller Soft Start Stability via Lower Bridge Switch Control
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Solution Overview
Problem
Conventional DC-to-DC buck power converters experience instability during the initial soft start period due to weak voltage releasing ability, leading to unstable output curves, especially when the input voltage is high and the slew rate is low.
Innovation Solution
A DC-to-DC controller with a time signal generating unit and a time signal control circuit that introduces a preset dead time during each operation cycle period, turning off both bridge switches for a first preset time and then turning on the lower bridge switch for a second preset time, facilitating voltage releasing through the body diode to prevent overshoot and enabling overcurrent protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper bridge switch is turned off and the lower bridge switch is turned on during soft start period, then the inductance current flows back toward ground end for voltage releasing, but the output voltage becomes unstable due to weak voltage releasing ability when output voltage is low
Solution Approach 1:
The patent applies preliminary action by forcing the lower bridge switch to turn on at least once during the soft start period before normal operation begins. This preliminary action ensures that voltage releasing capability is established early when the output voltage is still low and the voltage releasing ability would otherwise be weak. The control circuit detects the soft start period and actively controls the lower bridge switch to conduct, preventing output instability before it occurs.
2Reliability
If the lower bridge switch is turned on continuously to maintain voltage releasing ability, then output stability improves, but overcurrent protection capability deteriorates
Solution Approach 1:
The patent applies periodic action by controlling the lower bridge switch to turn on at specific intervals rather than continuously. During the soft start period, the lower bridge switch is forced to conduct at least once to establish voltage releasing ability. After soft start completes, the circuit returns to normal periodic PWM control with proper dead time. This periodic approach maintains stability during the critical startup phase while preserving overcurrent protection during normal operation.
Solution Approach 2:
The patent applies preliminary action by temporarily modifying the switch control strategy only during the soft start period. The lower bridge switch is forced to turn on during this preliminary phase to build up voltage releasing capability. Once soft start is complete and output voltage is stable, the control returns to normal operation with standard overcurrent protection. This time-limited preliminary action resolves the contradiction by applying the non-standard control only when necessary.
3Stability of the object's composition
If the slew rate is kept low for smooth voltage transition during soft start, then output ripple reduces, but output stability deteriorates when input voltage is high
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the control parameters of the bridge switches based on the operating phase. During soft start, the lower bridge switch is forced to conduct with a minimum on-time regardless of the PWM duty cycle, ensuring sufficient voltage releasing ability even when slew rate is low. After soft start, the circuit transitions to normal PWM control where the duty cycle smoothly regulates the output. This parameter change approach maintains low ripple during soft start while ensuring stability through active lower switch control.
Data Source
AI summary
A DC-to-DC controller and a control method thereof are provided. The DC-to-DC controller couples to an output stage, and the output stage provides an output voltage and includes an upper bridge switch and a lower bridge switch. The DC-to-DC controller includes a time signal generating unit and a time signal control circuit. The time signal control circuit couples to the time signal generating unit and receives a preset voltage and the output voltage. During a soft start period, if the output voltage is lower than the preset voltage, after the upper bridge switch is turned off and before the upper bridge switch is turned on again, the time signal control circuit turns off the upper bridge switch and the lower bridge switch for a first preset time and turns on the lower bridge switch for a second preset time.