Power Supply IC With Boosted Capacitor Hold-Up Against UVLO Reset
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Solution Overview
Problem
Power supply circuits face challenges in maintaining a stable power supply voltage due to drops in the voltage across the auxiliary coil, which can lead to under voltage protection and reset of the integrated circuit.
Innovation Solution
An integrated circuit is designed to control the switching of a transistor in a power supply circuit, incorporating a booster circuit to generate a boost voltage based on the voltage across the auxiliary coil, and a charging circuit to charge a capacitor when the power supply voltage drops below a certain threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching period of the power transistor increases due to decreased load current, then the power supply efficiency improves, but the voltage across the auxiliary coil drops causing power supply voltage instability
Solution Approach 1:
The patent introduces a capacitor as an intermediary energy storage element between the auxiliary coil and the power supply circuit. This capacitor accumulates energy during periods when the auxiliary coil generates sufficient voltage and releases it when the voltage drops, thereby mediating the instability caused by varying switching periods and load conditions.
Solution Approach 2:
The patent changes the electrical parameters of the power supply system by introducing a capacitor with specific capacitance value. This parameter change enables the system to maintain stable power supply voltage across different operating conditions, particularly when switching period varies with load current.
2Reliability
If the power supply voltage drops below the threshold, then the under voltage protection circuit operates to protect the system, but the integrated circuit resets causing operational interruption
Solution Approach 1:
The capacitor performs preliminary action by pre-storing energy in advance before the power supply voltage drops. This advance energy storage prevents the voltage from falling below the reset threshold, thereby preventing the integrated circuit from resetting and maintaining operational continuity while still providing under voltage protection.
Solution Approach 2:
The capacitor provides beforehand cushioning by creating an energy buffer that cushions against voltage drops. This cushioning effect prevents sudden voltage drops from triggering the under voltage protection reset, allowing the system to continue operating smoothly during transient conditions.
3Device complexity
If the voltage across the auxiliary coil is used to generate power supply voltage, then the circuit complexity is reduced, but the power supply voltage becomes sensitive to load current variations
Solution Approach 1:
The capacitor serves as an intermediary that decouples the direct relationship between the auxiliary coil voltage and the power supply voltage. This intermediary element filters out the sensitivity to load current variations while maintaining the simplicity of using the auxiliary coil for power supply generation, thus preserving low circuit complexity while improving voltage stability.
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 solution effectively maintains a stable power supply voltage by generating a boost voltage to charge the capacitor, preventing drops in the power supply voltage and reducing the likelihood of under voltage protection and reset.
Implementation Method 1
the voltage across the auxiliary coil is generated with the integrated circuit switching the power transistor
Implementation Method 2
a first capacitor, a first diode configured to charge the first capacitor, based on a voltage across the auxiliary coil, upon turning off of the transistor
Data Source
AI summary
An integrated circuit for a power supply circuit that generates an output voltage from an input voltage. The power supply circuit includes a transformer, a transistor controlling an inductor current flowing through a primary coil of the transformer, a first capacitor, and a first diode charging the first capacitor. The integrated circuit is configured to control switching of the transistor. The integrated circuit includes a first terminal configured to receive a voltage across the first capacitor; a second terminal configured to receive a feedback voltage corresponding to the output voltage; a driving signal output circuit configured to output a driving signal to increase a switching period of the transistor, in response to a decrease in a load current; a driver circuit configured to drive the transistor in response to the driving signal; and a determination circuit configured to determine whether the power supply voltage drops below a first voltage.