High-Side Switch On-Time Control for Clamping Voltage Spikes
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Solution Overview
Problem
Traditional switching mode power supplies face challenges in efficiently controlling the on-time of high-side switches, leading to potential damage from voltage spikes across clamping capacitors due to unpredictable leakage inductance energy and varying voltage levels during mass production.
Innovation Solution
A control circuit for switching mode power supplies that includes a voltage detection circuit, an on-time adjustment circuit, and a driving circuit, which detects voltage signals at the high-side switch, compares them to a threshold, and adjusts the on-time of the high-side switch to prevent voltage spikes by extending or shortening its on-time based on the detected voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the on-time of the high-side switch is extended to transfer more leakage inductance energy, then the energy transfer is improved, but the voltage spike across the clamping capacitor increases and may damage components
Solution Approach 1:
The patent applies dynamics by making the on-time of the high-side switch variable rather than fixed. The control circuit dynamically adjusts the on-time based on detected voltage levels at the switch terminal, extending it when voltage is low to transfer more energy, and shortening it when voltage rises to prevent dangerous spikes. This dynamic adaptation resolves the contradiction between maximizing energy transfer and preventing voltage damage.
Solution Approach 2:
The patent implements feedback by using a detection circuit to monitor the voltage signal at the terminal of the high-side switch in real-time. This feedback information is fed back to the control circuit, which then adjusts the on-time accordingly. The closed-loop feedback mechanism enables the system to automatically balance energy transfer efficiency with voltage spike prevention.
2Device complexity
If a fixed on-time is used for the high-side switch, then the control is simplified, but the voltage spikes cannot be suppressed under varying voltage conditions
Solution Approach 1:
The patent transforms the static, fixed on-time control into a dynamic, adaptive control system. By introducing voltage detection and conditional adjustment mechanisms, the system automatically adapts its on-time to varying voltage conditions, thereby suppressing voltage spikes while maintaining reasonable control complexity through systematic design.
3Reliability
If the on-time of the high-side switch is shortened to reduce voltage spikes, then component safety is improved, but the leakage inductance energy transfer becomes insufficient
Solution Approach 1:
The patent resolves this contradiction by making the on-time dynamic rather than statically short. The system extends the on-time when voltage conditions permit (to maximize energy transfer) and shortens it only when necessary (to prevent voltage spikes). This dynamic behavior ensures both component safety and sufficient energy transfer are achieved optimally.
Solution Approach 2:
The feedback mechanism monitors voltage levels and adjusts on-time accordingly, ensuring the system operates in the optimal region that balances energy transfer efficiency with component safety. The feedback loop prevents premature switching off that would limit energy transfer while avoiding excessive on-time that would cause voltage damage.
Data Source
AI summary
A control circuit for a switching mode power supply is disclosed herein. The switching mode power supply has a primary-side circuit, the primary-side circuit has a first switch, a second switch, and a clamping capacitor. The control circuit includes a voltage detection circuit, an on-time adjustment circuit, and a driving circuit. The voltage detection circuit is coupled to the first terminal of the first switch and configured to detect a voltage signal at the first terminal of the first switch. The on-time adjustment circuit is configured to provide a first on-time signal to adjust an on-time of the first switch according to the voltage signal at the first terminal of the first switch. The driving circuit is configured to provide a driving signal to a control terminal of the first switch according to the first on-time signal.