Power Supply Clamp Circuit for Fast Startup and Overcurrent Control
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Solution Overview
Problem
Conventional switching regulators experience a slow rise in output voltage and high maximum current at startup, leading to inefficiency and reduced response speed, especially in applications like PWM brightness adjustment units for liquid crystal panels.
Innovation Solution
A power supply device with a clamp circuit that stepwise increases the upper limit value of the error voltage after startup, and includes a soft-start interruption circuit to manage the comparison voltage and enable signal changes, reducing the maximum current and shortening the rise time of the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a soft-start circuit is used to prevent overcurrent at startup, then reliability is improved, but the rise time of output voltage increases and productivity deteriorates
Solution Approach 1:
The clamp circuit dynamically adjusts the error voltage upper limit in multiple stages: initially clamping at a first upper limit during soft-start to prevent overcurrent, then switching to a second upper limit after soft-start completion to enable faster response. This dynamic parameter adjustment resolves the contradiction between overcurrent protection and fast response capability.
2Reliability
If conventional soft-start is used, then reliability is improved, but energy loss increases due to prolonged startup duration
Solution Approach 1:
The circuit employs periodic multi-stage clamp control during startup: first clamping the error voltage to limit current, then releasing to the second upper limit to complete startup. This staged periodic action reduces the duration of high-power startup conditions, thereby reducing energy loss while maintaining reliable startup control.
3Productivity
If the error voltage upper limit is increased to reduce rise time, then productivity is improved, but overcurrent may occur during startup
Solution Approach 1:
The soft-start circuit performs preliminary action by clamping the error voltage to the first upper limit before the main startup process. This preliminary current limitation prevents overcurrent, and only after this protective phase completes does the circuit allow the error voltage to reach the second upper limit for fast response, thus avoiding overcurrent while achieving fast startup.
4Productivity
If multi-stage clamp control is implemented, then productivity and energy efficiency are improved, but device complexity increases
Solution Approach 1:
The multi-stage clamp control functionality is merged into the existing error amplifier and clamp circuit structure. By utilizing the existing error amplifier to generate the error voltage and the clamp circuit to enforce upper limits, the patent achieves complex multi-stage control without proportionally increasing device complexity. The control logic integrates with the PWM comparator and soft-start circuit that already exist in switching regulators.
Data Source
AI summary
A power supply device includes a clamp circuit that increases the upper limit value of an error voltage stepwise after the device is started up. This makes it possible to shorten the rise time of an output voltage and to reduce the maximum current at start-up.