Switching Power Supply Circuit with Dynamic Overcurrent Protection
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Solution Overview
Problem
The existing switching power supply circuits with insulated transformers, particularly those using multiple secondary winding wires, face challenges in reducing component size and cost due to inadequate overcurrent protection mechanisms, leading to heat issues and increased size, especially when abnormal conditions occur, and are not suitable for low-voltage direct-current power supplies without auxiliary winding wires.
Innovation Solution
A switching power supply circuit with an insulated transformer, a switching element, a capacitor, and an IC for power supply control, along with a secondary-winding-wire-conduction-time detecting unit that estimates the current flow time and outputs detection results to a control circuit, allowing for optimized operation and reduced component sizes by adjusting the overcurrent protection level dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the overcurrent protection level is set high to allow sufficient power energy accumulation during start time, then the capacitor can be charged to the commanded voltage, but the switching element and diode require large heat capacities to handle excessive current during abnormal conditions
Solution Approach 1:
The overcurrent protection level is made dynamically adjustable based on the operating state. During start time when the capacitor voltage is below the commanded voltage, the protection level is set to a first value that allows sufficient current for charging. During steady state when the capacitor voltage reaches the commanded voltage, the protection level switches to a second value that is lower than the first value, providing stricter protection and enabling the use of switching elements and diodes with smaller heat capacities.
2Use of energy by moving object
If the switching element is forcibly turned off by overcurrent protection during start time, then the capacitor can be charged, but the switching element cannot be turned on again until the overcurrent protection is released
Solution Approach 1:
The control system dynamically adjusts the overcurrent protection threshold based on the capacitor voltage state. When the capacitor voltage is below the commanded voltage (start time), the protection threshold is raised to allow higher current flow that can charge the capacitor effectively. When the capacitor voltage reaches the commanded voltage (steady state), the threshold is lowered to provide immediate protection. This dynamic adjustment eliminates the unnecessary turn-on delay that would occur with a fixed low threshold.
3Reliability
If components with large heat capacities are used to prevent thermal destruction, then the switching element and diode can handle excessive current, but the size of the switching power supply circuit increases
Solution Approach 1:
The overcurrent protection level parameter is changed based on the operating state. During start time, the protection level is set to a higher first value that permits the capacitor to charge to the commanded voltage. During steady state, the protection level is reduced to a lower second value, which enables the use of switching elements and diodes with smaller heat capacities and reduced sizes, thereby reducing the overall circuit size while maintaining reliability.
4Reliability
If the overcurrent protection level current value is reduced to quickly interrupt operation during abnormality, then thermal destruction is prevented, but the capacitor cannot be charged to the commanded voltage during start time
Solution Approach 1:
The overcurrent protection level is dynamically adjusted based on the capacitor voltage relative to the commanded voltage. When the capacitor voltage is below the commanded voltage during start time, the protection level is set to a first value that is sufficiently high to allow the capacitor to charge. When the capacitor voltage reaches the commanded voltage in steady state, the protection level switches to a lower second value that provides quick interruption capability during abnormal conditions. This resolves the contradiction by making the protection level adaptive to the charging state.
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
This configuration reduces the size and heat capacity requirements of the switching element, diode, and transformer, preventing magnetic saturation and thermal damage, while maintaining efficient power supply and reducing overall costs.
Implementation Method 1
an insulated transformer configured by a primary winding wire and one or a plurality of secondary winding wires; a switching element that is connected to the primary winding wire of the insulated transformer in series
Implementation Method 2
a capacitor connected to the secondary winding wire(s) of the insulated transformer via the diode
Implementation Method 3
a diode connected to the secondary winding wire(s) of the insulated transformer
Data Source
AI summary
A switching power supply circuit includes a switching element connected to a primary winding wire of a transformer in series, capacitors connected to secondary winding wires of the transformer via diodes, and an IC for power supply control that controls ON/OFF operation of the switching element on the basis of a charged voltage of the capacitors. Commanded voltages are charged in the capacitors after electric power is supplied to a main power supply, and further, after the elapse of a delay time set in advance, a control circuit, which controls the entire apparatus, controls a main circuit and a peripheral apparatus circuit to start operations.