Dynamic Hysteresis Control for Soft-Start in Power Converters
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Solution Overview
Problem
Existing power supply circuits face issues with surge currents and output voltage overshoot during soft-start processes due to limitations in device technology and input voltage range, leading to reliability and malfunction concerns.
Innovation Solution
A power supply circuit with a hysteresis control circuit that dynamically adjusts the hysteresis of a comparator based on feedback and reference voltages during soft-start, preventing undesirable behaviors like current surges and voltage spikes by gradually activating hysteresis when the circuit reaches operational conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a soft-start process is implemented using a gradually ramped reference voltage, then in-rush currents and voltage spikes are reduced, but surge currents and output voltage overshoot still occur due to low feedback voltage values and comparator limitations
Solution Approach 1:
The hysteresis of the comparator is made dynamic by adjusting it based on the output voltage level. During soft-start when output voltage is low, hysteresis is reduced to prevent surge currents. As output voltage increases, hysteresis is increased to stabilize operation and prevent oscillations. This dynamic adjustment resolves the contradiction between preventing in-rush currents and avoiding output voltage overshoot.
Solution Approach 2:
The patent changes the hysteresis parameter of the comparator based on operating conditions (output voltage level). By modifying this parameter dynamically during the soft-start process and normal operation, the system adapts to different voltage levels and prevents both surge currents at low voltage and voltage overshoot at higher voltage levels.
2Temperature
If folded-cascode topologies are used as error comparators to handle low voltages, then low voltage operation is achieved, but power consumption, area, and gain are undesirable
Solution Approach 1:
Instead of using complex folded-cascode topologies, the patent achieves low voltage operation by dynamically adjusting the hysteresis parameter of a simpler comparator. This parameter adjustment allows the comparator to operate effectively across a wide voltage range without requiring the complex circuit topology, thereby reducing power consumption and area while maintaining low voltage capability.
Solution Approach 2:
The patent extracts the essential function of handling low voltages from the complex folded-cascode topology and implements it through a simpler comparator with dynamically adjusted hysteresis. This removes the unnecessary complexity while retaining the low voltage operation capability.
3Stability of the object's composition
If hysteresis is increased to prevent oscillations during normal operation, then stability is improved, but current and voltage limits are exceeded during soft-start
Solution Approach 1:
The hysteresis is made dynamic rather than fixed. During soft-start when output voltage is low, hysteresis is automatically reduced to prevent current and voltage spikes. During normal operation when output voltage is stable, hysteresis is increased to prevent oscillations and improve stability. This dynamic behavior resolves the contradiction between stability and preventing harmful spikes.
Solution Approach 2:
The system prepares for potential oscillations by having hysteresis adjustment mechanisms ready, but only applies high hysteresis when needed (during normal operation). During soft-start, the system preliminarily uses low hysteresis to avoid spikes, then transitions to high hysteresis once stable operation is achieved.
Data Source
AI summary
In one general aspect, a power supply circuit can include a power stage configured to be coupled to a power source and configured to deliver an output voltage to a load circuit, and can include a comparator coupled to the power stage and configured to receive a reference voltage. The power supply circuit can also include a hysteresis control circuit configured to receive at least one of a feedback voltage or a reference voltage and configured to change a hysteresis of the comparator in response to the at least one of the feedback voltage or the reference voltage during a soft-start of the power supply circuit.