Switching Regulator Slope Voltage Linearity Stabilization
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Solution Overview
Problem
Current mode control type switching regulators face instability and poor linearity in slope voltage generation, particularly when there is a large difference between input and output voltages, leading to unstable output voltage and potential defects.
Innovation Solution
A current mode control type switching regulator that includes a slope voltage generating circuit unit with an inductor current detecting circuit and a ramp voltage generating circuit, which detects the inductor current and generates a ramp voltage, allowing for the comparison of amplified voltage differences to control the switching element via a pulsed signal, thereby stabilizing the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional slope voltage generating circuit is used, then the circuit structure is simple, but the slope voltage has poor linearity and causes unstable operation when there is a large difference between input and output voltages
Solution Approach 1:
The slope voltage generating circuit is divided into two independent modules: an inductor current detecting circuit that converts inductor current to voltage, and a ramp voltage generating circuit that generates a linear ramp voltage. These two circuits are then combined through addition to produce the final slope voltage, improving linearity without excessive complexity
Solution Approach 2:
An operational amplifier is introduced as an intermediary element to accurately add the voltage from the inductor current detecting circuit and the ramp voltage. This intermediary ensures precise voltage summation and maintains the linearity of the resulting slope voltage, resolving the instability issue
2Productivity
If the on-time of the switching element is short, then the switching frequency increases, but the slope voltage generation becomes unstable due to poor linearity
Solution Approach 1:
The inductor current is detected and converted to voltage in advance during the switching on-period. This preliminary voltage generation, combined with the ramp voltage, ensures that the slope voltage is fully formed and linear before the switching element turns off, even when the on-time is very short
Solution Approach 2:
The circuit changes the parameter of slope voltage generation from a single delayed process to a dual-component process where the inductor current voltage and ramp voltage are combined. This parameter change ensures the slope voltage maintains proper linearity regardless of the switching duty cycle or on-time duration
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
The solution enables the generation of a slope voltage with favorable linearity and stable operation, even when the on-time of the switching element is short, ensuring a stable output voltage.
Implementation Method 1
an inductor current detecting circuit 110a detects a voltage drop caused when the switching transistor is on
Implementation Method 2
The operational amplifier circuit 111 controls a gate voltage of a PMOS transistor M111 so that a source voltage of the PMOS transistor M111 becomes the same voltage level as the voltage VLx
Implementation Method 3
a ramp capacitor charged by the constant current outputted by the constant current circuit through the offset voltage generating resistor
Implementation Method 4
add a voltage drop caused by the offset voltage generating resistor to a terminal voltage of the ramp capacitor
Data Source
AI summary
A switching regulator for converting input voltage to output voltage includes a switch; an inductor energized by input voltage by the switch; a rectifier for discharging the inductor; and a slope voltage generator for generating slope voltage inclined responsive to current of the inductor, amplifies a difference between reference voltage and divided output voltage, and compares the amplified voltage and the slope voltage to generate signal for controlling the switch. The slope voltage generator includes a detector for converting current flowing through the inductor when the switch is on into voltage; and a voltage generator for generating ramp voltage. These voltages are added as the slope voltage. The voltage generator includes constant current; a resistor; and a ramp capacitor charged by the constant current through the resistor. Voltage drop of the resistor is added to terminal voltage of the ramp capacitor to output the ramp voltage.