Switching Power Supply On-Time Accuracy Control
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Solution Overview
Problem
In switching power supplies, the practical on-time of the power switch can be greater than the ideal on-time due to comparator delays, leading to inefficiencies, especially when the duty cycle is small, and can result in high inductor currents and large ripple voltages during load recovery.
Innovation Solution
A control method and circuit that generates an ideal on-time signal based on input and output voltages, a ripple voltage signal with specific characteristics, and a regulating control signal to accurately drive the power switch, reducing delays and ensuring consistent on-time with the ideal on-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional control methods are used to drive the power switch, then the control circuit is simple, but the practical on-time deviates from the ideal on-time due to comparator delays, leading to high inductor currents and large ripple voltages
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing compensation values in a lookup table before they are needed. The compensation data, which accounts for comparator delays and circuit characteristics, is prepared in advance during system initialization or manufacturing. When control is needed, the pre-computed compensation values are directly retrieved and applied, eliminating the need for real-time complex calculations and reducing actual control delay impact on on-time accuracy.
Solution Approach 2:
The patent introduces an intermediary compensation mechanism between the ideal on-time signal and the actual power switch drive signal. A compensation signal is generated based on stored compensation data that accounts for comparator delays and circuit characteristics. This intermediary compensation signal adjusts the timing to bridge the gap between ideal and actual on-time, ensuring accurate power switch control without requiring complete redesign of the control architecture.
2Productivity
If the duty cycle is small, then the switching power supply operates efficiently, but the practical on-time becomes significantly greater than the ideal on-time due to comparator delays, causing inefficiencies
Solution Approach 1:
The patent applies preliminary anti-action by anticipating and counteracting the comparator delay effect before it impacts the on-time control. Compensation data is pre-calculated to specifically address the delay issues that occur at small duty cycles. This compensation signal is applied in advance to the control waveform, effectively canceling out the anticipated comparator delay and ensuring that the practical on-time matches the ideal on-time even when operating at high switching efficiency points with small duty cycles.
3Reliability
If no compensation is applied, then the control circuit is simple and fast, but inductor currents become excessively high and ripple voltages increase during load recovery
Solution Approach 1:
The patent applies local quality by providing targeted compensation specifically during critical operating conditions such as load recovery, rather than uniformly across all operating modes. The compensation data in the lookup table is selectively applied based on the current operating state, allowing the control circuit to maintain simplicity during normal operation while providing enhanced stability and current control during transient conditions like load recovery when it is most needed.
Data Source
AI summary
In one embodiment, a method of controlling a switching power supply can include: (i) generating an ideal on time signal according to an input voltage and an output voltage of the switching power supply; (ii) generating a ripple voltage signal having a predetermined constant value when a power switch of the switching power supply is on, and a linearly decreasing value when the power switch is off; (iii) generating a regulating voltage signal according to an output voltage sense signal and the ripple voltage signal; (iv) generating a regulating control signal by comparing the regulating voltage signal against a first reference signal; (v) generating an on time control signal according to the regulating control signal and the ideal on time signal; and (vi) generating a driving signal according to the on time control signal for driving the power switch.