Switched-Mode Power Supply Control for Zero-Voltage Mode Switching
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Solution Overview
Problem
Existing switched-mode power supplies face challenges in achieving zero voltage conduction, particularly due to the parasitic capacitor in switch transistors, which leads to significant switching losses during mode switching.
Innovation Solution
A control method and circuit for a switched-mode power supply that includes a main switch transistor and an auxiliary switch transistor, where the control circuit sets a first current curve and a first frequency curve based on an error compensation signal to control the on-off states of the switch transistors, ensuring zero voltage conduction by discharging the parasitic capacitor before mode switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switch transistor is turned on without discharging the parasitic capacitor first, then the switching speed is maintained, but significant switching loss is generated
Solution Approach 1:
The patent applies preliminary action by discharging the parasitic capacitor of the switch transistor before turning on the switch. The control circuit detects when the parasitic capacitor charge approaches zero and提前 (in advance) initiates the discharge process through the auxiliary switch transistor, ensuring the capacitor is sufficiently discharged before the main switch turns on, thereby reducing switching losses while maintaining controllable complexity
Solution Approach 2:
The patent introduces an auxiliary switch transistor as an intermediary component to discharge the parasitic capacitor. This auxiliary switch acts as a mediator between the main switch and the parasitic capacitor, providing a controlled discharge path that reduces the voltage across the main switch at turn-on, thereby reducing switching loss without requiring direct complex control of the main switch timing
2Productivity
If mode switching is performed without proper parasitic capacitor discharge, then the response speed is improved, but switching loss increases significantly
Solution Approach 1:
The patent implements feedback control by using the error amplifier circuit to detect the charge state of the parasitic capacitor and adjust the switching control accordingly. The feedback mechanism monitors the capacitor voltage and provides control signals to the auxiliary switch to ensure proper discharge timing, enabling fast mode switching with reduced switching loss through closed-loop control
3Loss of energy
If the parasitic capacitor is discharged before mode switching, then switching loss is reduced, but the control complexity increases
Solution Approach 1:
The control circuit is designed with multi-functionality to reduce overall complexity. The same control circuit that manages mode switching also handles the parasitic capacitor discharge control through the auxiliary switch. The error amplifier and control logic perform multiple functions including voltage detection, discharge timing control, and mode switching coordination, thereby reducing the need for separate dedicated circuits
Data Source
AI summary
A control method and control circuit of a switched-mode power supply, and the switched-mode power supply are provided. An operating mode of the switched-mode power supply is controlled in a first mode and a second mode according to an output feedback signal of the switched-mode power supply. One operating period of the first mode includes a switch period of a boundary conduction mode (BCM), and one operating period of the second mode includes N switch periods of BCMs and a switch period of a discontinuous conduction mode (DCM). The auxiliary switch transistor is turned on once to discharge a parasitic capacitor of the main switch transistor when the switched-mode power supply enters the next operating period from one operating period of the current second mode before the next operating period starts or the switched-mode power supply enters the first mode from the current second mode before the first mode starts.