Hysteretic Switching Regulator Refresh Cycles
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Solution Overview
Problem
Switching regulators face challenges at low loads, where the switching frequency drops, leading to issues such as bootstrap capacitor discharge and potential audio band noise, as they struggle to maintain efficient operation and avoid switching in the audio frequency range.
Innovation Solution
A method for operating a hysteretic synthetic current-mode switching regulator that involves generating PWM pulses based on a ramp voltage oscillating between upper and lower window voltages, with specific control mechanisms to refresh bootstrap capacitors and manage energy transfer to prevent output voltage increases and audio band suppression, including adjusting transconductance amplifier gains and implementing refresh cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the switching regulator operates at low loads, then power consumption is reduced, but the switching frequency drops causing bootstrap capacitor discharge and audio band noise
Solution Approach 1:
The patent implements periodic refresh cycles that force PWM pulses to occur at regular intervals regardless of load conditions. This periodic action maintains the switching frequency above audio band thresholds and ensures bootstrap capacitors are recharged regularly, preventing discharge while still allowing the regulator to operate at low loads for reduced power consumption.
2Loss of energy
If the switching frequency is reduced at low loads, then switching losses are decreased, but audio band noise is generated and bootstrap capacitors discharge
Solution Approach 1:
The patent applies different operational modes locally based on system state: during normal operation, the regulator reduces switching frequency to minimize switching losses, but during refresh cycles, it forces higher frequency operation to prevent audio band noise and bootstrap capacitor discharge. This local quality differentiation allows the system to optimize for different objectives at different times.
3Reliability
If refresh cycles are implemented to maintain bootstrap capacitor charge, then capacitor reliability is improved, but additional switching events are introduced
Solution Approach 1:
The refresh cycles are integrated into the continuous operation of the switching regulator rather than being separate interruptive events. The control circuit seamlessly transitions between normal PWM operation and refresh cycles, maintaining continuous useful action. This approach ensures bootstrap capacitor reliability while minimizing disruption to overall switching efficiency by keeping the regulator in an active switching state throughout.
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
This approach effectively maintains switching frequency, prevents output voltage rises, and suppresses audio band noise by ensuring energy balance and capacitor refresh, thereby improving regulator performance at low loads.
Implementation Method 1
adjusting transconductance amplifier gains
Implementation Method 2
energy (or charge) stored in the inductor
Data Source
AI summary
A method of operating a hysteretic synthetic current-mode switching regulator is disclosed. In the switching regulator, PWM pulses (PWM) are generated by a PWM generator (20; FIG. 7) in dependence upon a ramp voltage (VR) which oscillates between upper and lower window voltages (VW+, VW−). The ramp voltage depends on a control voltage (VC) which depends on current (IL) through an inductor (6). The method comprise determining whether a period (T) equal to or greater than a given period (TREFRESH) has elapsed without a PWM pulse being generated, upon a positive determination, causing the ramp voltage to be pulled up to or above the upper window voltage (VW+) for a given duration (ΔT) and when said given duration has elapsed, causing the ramp voltage to decrease until a rising edge of a PWM pulse is generated.