Voltage Converting Controller Dynamic Off-Time Control
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Solution Overview
Problem
The constant-turn-on time control mode in switching voltage converting circuits is limited by the minimal off-time, restricting the duty cycle of the high-side power switch and limiting the input voltage to a minimum value, which is not suitable for battery applications where voltage decreases over time.
Innovation Solution
A voltage converting controller that operates a high-side and low-side power switch with a high-side control signal and a low-side control signal, where the period of the high-side control signal is set to a constant value or positively correlated with the ideal duty cycle, allowing the input voltage to approach the output voltage without the constraints of minimal off-time, using a comparator, current sources, capacitors, and amplifiers to manage the duty cycle based on the output voltage and input voltage ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the minimal off-time is imposed on the high-side power switch, then the control signal noise interference is reduced, but the duty cycle is limited and the input voltage cannot approach the output voltage
Solution Approach 1:
The patent applies dynamics by making the off-time period dynamic rather than fixed. The controller adjusts the off-time period based on the duty cycle: when the duty cycle exceeds a threshold, the off-time period is extended beyond the minimal off-time. This dynamic adjustment allows the system to maintain control signal stability (by extending off-time when needed) while simultaneously enabling the input voltage to approach the output voltage (by allowing larger duty cycles), thus resolving the contradiction between reliability and adaptability.
2Device complexity
If the duty cycle is limited by minimal off-time, then the control circuit complexity is reduced, but the power conversion efficiency decreases
Solution Approach 1:
The patent uses dynamics to adjust the off-time period based on operating conditions. The controller monitors the duty cycle and dynamically extends the off-time period when the duty cycle exceeds a threshold, rather than imposing a fixed minimal off-time. This dynamic approach maintains relatively simple control circuitry while improving power conversion efficiency by allowing the duty cycle to reach values closer to 100% when needed, thereby reducing energy losses.
3Ease of operation
If the fixed pulse width is used in constant-turn-on time control, then the circuit operation is simplified, but the input voltage range is restricted
Solution Approach 1:
The patent applies dynamics by making the control signal period adaptive. While maintaining the simple constant-turn-on time control structure with fixed pulse width, the controller dynamically adjusts the period of the control signal based on the duty cycle. When the duty cycle exceeds a threshold, the period is extended, which effectively allows larger duty cycles and broader input voltage range without complicating the basic fixed pulse width control mechanism.
Data Source
AI summary
A voltage converting controller is applied to a switching voltage converting circuit, in which the voltage converting controller periodically operates a high-side power switch and a low-side power switch in the switching voltage converting circuit with a high-side control signal and a low-side control signal, respectively, so as to convert an input voltage into an output voltage via an inductor. Defining an ideal duty cycle as the rating value of the output voltage divided by the value of the input voltage, when the ideal duty cycle is less than one threshold duty cycle, then the period of the high-side control signal is a constant; and when the ideal duty cycle is greater than the threshold duty cycle, the period of the high-side control signal and the period of the ideal duty cycle are positively correlated.