SMPS COT Control Circuit for Stable Frequency at High Input Voltage
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Solution Overview
Problem
Conventional switched-mode power supply (SMPS) circuits in COT mode face suboptimal performance due to fixed on-time vs. input voltage relationships, leading to issues such as low switching frequencies at high voltages and significant crossover losses at high voltages, especially in applications with wide voltage ranges.
Innovation Solution
An SMPS control circuit with a signal conversion module and an on-time realization module that outputs a reference signal increasing at a decreasing rate with input voltage, maintaining the power transistor on for a time inversely proportional to the reference signal, using a functional relationship of S=a(Ln(b*VIN+c)+d, where S is the reference signal, VIN is the input voltage, and a, b, c, and d are constant coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a completely fixed on-time is used in COT mode, then the control circuit remains simple and easy to compensate, but the switching frequency drops too low at high input voltages, requiring high inductance
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed on-time to a dynamic on-time that varies with input voltage. The on-time is made inversely proportional to the input voltage through a control circuit that adjusts the on-time based on the detected input voltage level, allowing the switching frequency to remain relatively stable across different voltage conditions while keeping the control circuit relatively simple
2Speed
If the on-time is made inversely proportional to the input voltage to maintain constant switching frequency, then the switching frequency remains stable, but significant crossover losses occur at high voltages, reducing system efficiency
Solution Approach 1:
The patent applies parameter changes by modifying the on-time parameter based on the input voltage level. Specifically, the on-time is adjusted to be inversely proportional to the input voltage, which maintains constant switching frequency. The control circuit detects input voltage and dynamically adjusts the on-time parameter to optimize performance across different operating conditions
3Reliability
If conventional on-time vs. input voltage functional relationships are used, then the circuit operates reliably under standard conditions, but performance becomes suboptimal under wide voltage range conditions
Solution Approach 1:
The patent applies dynamics by making the on-time adaptive to input voltage changes. The control circuit dynamically adjusts the on-time based on the detected input voltage, allowing the power supply to maintain optimal performance across a wide voltage range while preserving operational reliability through controlled adaptation
Data Source
AI summary
An SMPS control circuit and a power chip are disclosed. The SMPS control circuit includes a signal conversion module configured to acquire an input voltage and output a reference signal. The reference signal increases as the input voltage increases at a rate decreasing as the input voltage increases. The reference signal is configured to turn on a power transistor and maintain it on for a period of time in inverse proportion to the reference signal. With this configuration, the SMPS control circuit operates in a COT mode combining, in a high-voltage range, advantages of both a complete COT mode and a mode with an on-time in inverse proportion to the input voltage, overcoming the problem with conventional power supply circuits of being configured with an on-time vs. input voltage functional relationship in a COT mode, which is suboptimal and problematic under some operating conditions.