Predictive Ripple Cancellation in SMPS Error Amplifier
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Solution Overview
Problem
Switching power supplies face inaccuracies in output voltage due to ripple in the feedback voltage, which affects the control voltage and can cause inaccuracy and interaction with slope compensation, especially at high duty cycles and transient situations.
Innovation Solution
A predicted ripple in the feedback voltage is generated based on recent switching cycles and either added to or subtracted from the reference voltage to cancel out the ripple component, ensuring a non-rippling control voltage is produced, thereby improving accuracy and reducing the need for excessive capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If ripple in the feedback voltage is allowed to pass to the error amplifier, then the circuit operates simply without additional components, but the control voltage becomes inaccurate and the error amplifier may operate out of its linear region
Solution Approach 1:
The patent generates a predicted ripple signal in advance based on previous switching cycle data, then uses this prediction to pre-compensate the reference voltage before it enters the error amplifier. This preliminary action prevents the ripple from affecting the control voltage accuracy and keeping the error amplifier in its linear region.
Solution Approach 2:
The patent implements a feedback mechanism where the actual feedback voltage is monitored, and its ripple characteristics are used to generate a predicted ripple signal that compensates for future ripple effects. This closed-loop approach continuously adjusts the compensation to maintain output voltage accuracy.
2Stability of the object's composition
If capacitance is increased to smooth out feedback voltage ripple, then the ripple is reduced, but the gain-bandwidth product decreases and transient response slows down
Solution Approach 1:
Instead of using capacitance to reactively smooth ripple, the patent predictively generates a ripple compensation signal based on previous cycle data. This allows the system to proactively counteract ripple effects without needing large capacitors, thereby maintaining fast transient response while achieving ripple reduction.
Solution Approach 2:
The patent creates a copy of the ripple signal through prediction based on previous cycles, then uses this copied ripple information to generate a compensating signal. This approach replicates the ripple characteristics without physically smoothing the feedback voltage through capacitance.
3Device complexity
If the error amplifier operates with rippling control voltage, then the circuit remains simple, but the comparator tripping becomes inaccurate and slope compensation interacts adversely
Solution Approach 1:
The patent pre-generates a predicted ripple signal before the actual ripple affects the control voltage. This predicted signal is used to adjust the reference voltage in advance, ensuring that the comparator receives an accurate reference level despite the presence of feedback ripple, thereby maintaining precise tripping accuracy.
Solution Approach 2:
The patent introduces a ripple prediction and compensation mechanism as an intermediary between the feedback voltage and the error amplifier. This intermediary process filters out the harmful effects of ripple through prediction and compensation, allowing the rest of the circuit to remain simple while achieving accurate comparator operation.
Data Source
AI summary
A predicted ripple in the feedback voltage of a switching converter is generated, based on the ripple over a certain number of recent switching cycles. The DC portion of the feedback voltage is filtered out. This predicted feedback voltage ripple is then added to a fixed reference voltage to create a compensated reference voltage. The compensated reference voltage is applied to the non-inverting input of an error amplifier, and the feedback voltage (having a DC component and ripple) is applied to the inverting input of the error amplifier. Thus, substantially the same ripple component is applied to both inputs and cancels out. Therefore, the output of the error amplifier is not affected by the ripple in the feedback voltage, and a non-rippling control voltage is generated by the error amplifier. As a result, the gain-bandwidth product of the converter can be increased for faster response to transients.