Power Converter Control Circuit Stabilizing Inductor Current
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Solution Overview
Problem
Conventional power conversion circuits with small parasitic resistance in output capacitors experience instability due to phase differences between output voltage ripple and pulse width modulation signals, leading to ringing phenomena and unstable inductor currents.
Innovation Solution
A control circuit for power converters that includes a sensing circuit, ramp signal generator, error amplifier, comparator, and pulse width modulation circuit, which senses the inductor current and adjusts the slope of the ramp signal to prevent ringing by generating a gentler falling slope when the current sensing signal is larger, thereby stabilizing the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a ceramic capacitor with small parasitic resistance is used as the output capacitor, then the power conversion efficiency is improved, but the system stability deteriorates due to phase difference between output voltage ripple and PWM signal
Solution Approach 1:
The patent introduces a dummy resistor connected in parallel with the output capacitor to simulate the ESR of traditional capacitors. This dummy resistor acts as an intermediary element that restores the phase difference between output voltage and inductor current, thereby maintaining system stability while allowing the use of low-ESR ceramic capacitors for improved efficiency
Solution Approach 2:
The patent modifies the electrical parameters of the output stage by adding the dummy resistor, which changes the impedance characteristics and phase relationships in the feedback loop. This parameter change allows the system to achieve both low loss (through ceramic capacitor) and stability (through modified impedance profile)
2Loss of energy
If the output resistance is small, then the power loss is reduced, but ringing phenomenon occurs causing unstable inductor current
Solution Approach 1:
The dummy resistor serves as a mediator that introduces artificial damping into the system. By placing this resistor in parallel with the low-ESR ceramic capacitor, it provides the necessary phase shift and damping effect to prevent ringing and current instability, while the overall power loss remains low due to the inherently low resistance
3Device complexity
If conventional feedback control is used with small ESR capacitors, then the device complexity is reduced, but the control precision deteriorates due to phase difference effects
Solution Approach 1:
The dummy resistor acts as a passive intermediary that automatically provides the necessary phase compensation without requiring complex active control circuits. This maintains simplicity in the control architecture while significantly improving output voltage regulation precision by restoring proper phase relationships in the feedback loop
Data Source
AI summary
A control circuit of a power converter includes a sensing circuit, a ramp signal generator, an error amplifier, a comparator and a PWM circuit. The sensing circuit, coupled to a first output circuit, provides a current sensing signal. The ramp signal generator, coupled to the sensing circuit, receives the current sensing signal to provide a ramp signal. The error amplifier receives a reference voltage and an output feedback voltage of the power converter to provide an error amplification signal. The comparator, coupled to the ramp signal generator and the error amplifier, provides a control signal according to the ramp signal and the error amplification signal. The PWM circuit, coupled between the comparator and the first output circuit, receives the control signal and provides a PWM signal to control the first output circuit. The ramp signal generator adjusts a slope of the ramp signal according to the current sensing signal.