Voltage Regulator On-Time Extension for Duty Cycle Limits
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Solution Overview
Problem
Fixed on-time control in DC-to-DC switching voltage regulators results in an upper limit on duty cycle, leading to output voltage undershoot when input voltage decreases or load current suddenly increases, which cannot be adequately addressed by existing technologies.
Innovation Solution
Incorporating an on-time extension circuit that lengthens the on-time of the high side transistor in response to output voltage undershoot, allowing the load current to step up quickly and reducing the magnitude of undershoot by extending the on-time during periods of voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed on-time control is used for the HS transistor, then the control circuit is simple and reliable, but the duty cycle is limited and output voltage undershoot occurs when input voltage decreases
Solution Approach 1:
The patent implements dynamic on-time control where the HS transistor on-time is no longer fixed but is extended dynamically based on output voltage feedback. When output voltage drops below a threshold, the on-time is extended to allow higher duty cycles, thus adapting the control to varying input voltage conditions and preventing undershoot while maintaining circuit reliability.
Solution Approach 2:
The patent changes the on-time parameter from a fixed value to a variable parameter that can be extended when needed. By monitoring output voltage and extending on-time during voltage drops, the system adjusts this critical timing parameter to achieve higher duty cycles and maintain stable output voltage under varying input conditions.
2Stability of the object's composition
If fixed on-time control is used, then the switching frequency is stable, but the load current cannot step up quickly causing large output voltage undershoot
Solution Approach 1:
The patent applies preliminary action by extending the HS transistor on-time before the output voltage undershoot becomes severe. When voltage drops are detected, the on-time extension allows the inductor current to build up more quickly in advance, preparing the system to handle sudden load increases and reducing the magnitude of undershoot while maintaining stable switching operation.
3Measurement precision
If the duty cycle is increased to compensate for lower input voltage, then the output voltage regulation improves, but the on-time extension is needed to achieve higher duty cycle levels
Solution Approach 1:
The patent employs feedback control by monitoring the output voltage and using this information to dynamically extend the HS transistor on-time when voltage drops occur. This feedback mechanism enables the system to achieve higher duty cycles and improved voltage regulation precision by adjusting on-time based on actual output conditions, while keeping the control circuit relatively simple through straightforward voltage comparison and timing extension logic.
Data Source
AI summary
A voltage regulator circuit includes a high side (HS) transistor having a control input and a low side (LS) transistor having a control input. The LS transistor is coupled to the HS transistor at a switching terminal. A comparator has first and second inputs and an output. A first resistor is coupled to the switching terminal. A second resistor is coupled between the first resistor and the second input of the comparator. A capacitor is coupled between a second resistor terminal of the second resistor and ground. A switch has first and second switch terminals and a control input. The first switch terminal is coupled to the first resistor terminal of the second resistor, and the second switch terminal is coupled to the second resistor terminal. A delay circuit has an input and an output. The output of the delay circuit is coupled to the control input of the switch.