Switching Power Supply Coil Current Emulation Circuit
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Solution Overview
Problem
Conventional switching power supply circuits face challenges in utilizing low ESR capacitors for load capacity while maintaining stable operation at high oscillation frequencies and achieving accurate output voltage regulation, especially in buck-boost modes, due to the need for coil current sensing which increases circuit complexity and power consumption.
Innovation Solution
A switching power supply circuit that employs a coil current emulation circuit and a control circuit for on-off control, eliminating the need for a sense resistor by generating an output voltage similar to the coil current, allowing stable operation with low ESR capacitors in buck, boost, and buck-boost modes, even at high frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sense resistor and current amplifier are used to detect coil current, then the switching power supply circuit can operate in buck-boost mode with stable control, but the circuit scale is widened and current consumption is increased
Solution Approach 1:
The patent creates a copy of the coil current waveform using a capacitor connected between the switching element and ground. This capacitor voltage waveform replicates the coil current characteristics without requiring physical current sensing components, thereby simplifying the circuit while maintaining control stability
Solution Approach 2:
The patent extracts the essential information (coil current waveform) from the complex sensing circuit by using the capacitor voltage directly as the emulation signal, eliminating the need for sense resistors and current amplifiers
2Loss of energy
If a sense resistor with low value is selected to reduce influence on output voltage conversion efficiency, then efficiency is improved, but an amplifier with low offset voltage conforming to low input voltage must be used increasing circuit complexity
Solution Approach 1:
The capacitor voltage waveform serves as a copy of the coil current, eliminating the need for low-value sense resistors and specialized low-offset amplifiers, thus maintaining conversion efficiency without imposing strict amplifier requirements
3Measurement precision
If large transistors of input differential pair are used or multiple transistors are used with trimming adjustment, then measurement precision is improved, but layout pattern is greatly influenced and circuit scale is widened
Solution Approach 1:
The capacitor voltage waveform provides a direct copy of the coil current characteristics without requiring large transistors or trimming adjustments, achieving precise detection while simplifying the layout pattern
4Difficulty of detecting and measuring
If conventional coil current detection circuit is used, then coil current can be detected, but current consumption is increased to drive high speed comparator impedimenting high speed operation
Solution Approach 1:
The capacitor voltage waveform directly emulates the coil current without requiring high-speed comparators or high-current amplifiers, enabling coil current detection with reduced current consumption that does not impede high-speed operation
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 solution simplifies coil current detection, reduces circuit complexity, and enables stable operation at high frequencies, maintaining accurate output voltage regulation without the need for sense resistors, thus improving efficiency and layout flexibility.
Implementation Method 1
the coil current emulation circuit has a CR integration circuit, and provides an output terminal, between a capacitor and a resistor constituting the CR integration circuit, for outputting the output voltage similar to the coil current
Data Source
AI summary
A switching power supply circuit, which keeps an output voltage constant highly accurately by a buck-boost action, is provided. The switching power supply circuit comprises: a switching circuit formed by combining four switching elements with a coil in the shape of H; a coil current emulation circuit for generating an output voltage VC similar to a coil current; and a control circuit which, based on a feedback voltage representing an output voltage VO of the switching circuit, and the output voltage VC, performs on-off control of the switching circuit. The coil current emulation circuit has a CR integration circuit to generate the output voltage VC similar to the coil current. One of three voltages is applied to one terminal of the CR integration circuit, while a voltage proportional to the output voltage VO is applied to the other terminal of the CR integration circuit. The three voltages are a voltage proportional to an input voltage VIN, a ground voltage, and a voltage proportional to the sum of the input voltage VIN and the output voltage VO.