Switching Power Supply Shutdown Circuit for Overcurrent Protection
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Solution Overview
Problem
Conventional switching power supply circuits fail to effectively control bias voltage during overcurrent or load short-circuit conditions, leading to potential overheating and failure due to continuous operation beyond designed parameters.
Innovation Solution
A shut-down circuit is introduced, comprising a second rectifying element, a current sense resistor, and a power control circuit that controls the switching element's on-time ratio and stops the switching operation when the bias voltage falls below a set voltage, preventing continuous operation and overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If no protection circuit is added and the switching power supply operates continuously, then the circuit complexity is reduced, but the reliability deteriorates due to potential overheating and component damage during overcurrent or load short-circuit conditions
Solution Approach 1:
The switching power supply circuit automatically detects overcurrent or load short-circuit conditions through the bias voltage drop and shuts down without requiring external protection circuits. The system serves itself by using its own operational parameters (bias voltage) to trigger protection, eliminating the need for separate protection circuitry while maintaining reliability.
Solution Approach 2:
The circuit uses feedback from the bias voltage to the power control IC to detect abnormal conditions. When the bias voltage drops below the threshold during overcurrent or short-circuit, this feedback signal triggers the shutdown sequence, creating a closed-loop protection mechanism that balances simplicity with reliability.
2Productivity
If the switching power supply operates continuously without shutdown capability, then the productivity is improved, but the temperature increases leading to component failure
Solution Approach 1:
The protection circuit implements periodic operation by alternating between normal operation and shutdown states. During overcurrent or short-circuit conditions, the circuit periodically shuts down when bias voltage drops below threshold, then restarts when voltage recovers, creating a pulsed operation pattern that prevents continuous heat accumulation while maintaining some level of power delivery.
Solution Approach 2:
The circuit prepares for thermal damage by implementing preventive shutdown before components reach critical temperatures. The bias voltage threshold is set to trigger shutdown at safe operating margins, cushioning against potential thermal runaway and component failure before they can occur.
3Reliability
If the bias voltage is allowed to drop to the stop voltage for power supply control IC, then the intermittent operation is achieved for protection, but the time delay increases before shutdown occurs
Solution Approach 1:
The power control IC is configured to shutdown at a voltage threshold higher than the absolute stop voltage. This preliminary action triggers the shutdown sequence before the bias voltage reaches the critical stop voltage, reducing the time delay while still achieving effective protection. The system acts in advance of the worst-case scenario.
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
The shut-down circuit ensures the switching power supply stops operation when the bias voltage drops below the set voltage, reducing heat generation and preventing component failure by implementing intermittent operation during overcurrent or load short-circuit conditions.
Implementation Method 1
a first rectifying element (102) connected to a commercial power supply (101); a first capacitor (103) connected to the first rectifying element (102), for smoothing a direct-current voltage rectified by the first rectifying element (102)
Implementation Method 2
a transformer (120) having a primary winding (121), a secondary winding (122), and an auxiliary winding (123)
Implementation Method 3
a second rectifying element (118) connected to the auxiliary winding (123)
Implementation Method 4
a switching element (110) configured to switch the direct-current voltage from the first capacitor (103) to be supplied to the primary winding (121); a power control circuit (114) configured to control the switching element (110)
Implementation Method 5
a current sense resistor (111) configured to detect a magnitude of a primary current flow through the primary winding (121)
Data Source
AI summary
A rectifying element is connected to an auxiliary winding. The shut-down circuit receives a bias voltage output from the rectifying element. A shut-down circuit stops supply of power to a power supply terminal of the power supply control IC when the bias voltage is less than a set voltage. A power supply control IC controls a ratio of on-time to a switching cycle of the switching element, based on a current sensing voltage generated at a current sense resistor. The power supply control IC causes the switching operation of the switching element to stop when a voltage at the power supply terminal decreases to a stop voltage or less.