PWM Power Supply Feedback Circuit for Overvoltage Protection
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Solution Overview
Problem
Conventional power supply circuits for LCD devices are prone to damage when external AC voltage increases suddenly, leading to excessive voltage and current, which can disrupt normal operation and cause burnout.
Innovation Solution
Incorporating a transformer with an auxiliary winding and a feedback circuit that feeds the transformer's operating state back to a pulse width modulation circuit, allowing for control signals to be sent to turn off the transistor when excessive energy is detected, preventing energy from exceeding safe thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transistor is turned on continuously to convert AC voltage to DC voltage, then the power supply circuit can operate and provide output voltage, but when external AC voltage increases suddenly, excessive electrical energy is stored in the primary winding, causing overvoltage and current that can damage the circuit
Solution Approach 1:
The patent introduces a feedback circuit that includes an auxiliary winding on the transformer and a feedback resistor connected to a feedback port on the PWM circuit. The auxiliary winding generates a feedback signal proportional to the primary winding current, which is fed back to the PWM circuit. When the feedback signal exceeds a reference voltage, the PWM circuit automatically adjusts or shuts off the transistor switching, preventing excessive energy storage and protecting the circuit from overvoltage and overcurrent damage.
2Reliability
If no feedback mechanism is implemented, then the circuit structure remains simple, but the power supply circuit cannot detect excessive energy storage and is prone to burnout when AC voltage increases suddenly
Solution Approach 1:
The feedback mechanism adds minimal components: an auxiliary winding on the transformer core and a feedback resistor connected to the PWM circuit's feedback port. This simple feedback arrangement enables the circuit to detect excessive energy storage through the feedback signal and automatically respond by adjusting the transistor switching via the PWM circuit, providing protection without significantly increasing overall circuit complexity.
Solution Approach 2:
The auxiliary winding acts as an intermediary element that couples the primary winding's energy state to the PWM control circuit. It transforms the magnetic flux in the primary winding into an electrical feedback signal that the PWM circuit can process, enabling indirect detection and control of energy storage levels without direct measurement of current or voltage in the main power path.
3Stability of the object's composition
If the transistor switching is not controlled, then the power conversion process is continuous and simple, but the output voltage becomes unstable and cannot maintain constant DC voltage when input AC voltage fluctuates
Solution Approach 1:
The transistor is controlled to switch periodically rather than operating continuously. The PWM circuit generates periodic switching signals that turn the transistor on and off at controlled intervals. This periodic switching allows the circuit to regulate energy transfer in discrete amounts, maintaining stable output voltage even when input AC voltage fluctuates, while the feedback mechanism dynamically adjusts the switching duty cycle to compensate for voltage variations.
Solution Approach 2:
The feedback circuit continuously monitors the energy storage state through the auxiliary winding and adjusts the transistor switching control accordingly. When the feedback signal indicates excessive energy storage or voltage deviation, the PWM circuit modifies the switching timing or duty cycle to correct the output, ensuring stable DC voltage maintenance despite input fluctuations.
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 solution maintains constant DC voltage output and reduces the risk of power supply circuit burnout by preventing excessive energy storage, ensuring stable operation even with sudden increases in external AC voltage.
Implementation Method 1
When the transistor is turned off, electrical energy stored in the primary winding is transmitted to the secondary winding
Implementation Method 2
at least one feedback circuit feeding an operating state of the transformer back to the pulse width modulation circuit
Data Source
AI summary
An exemplary power supply circuit (20) includes a first commutating and filter circuit (21), a transformer (24), a second commutating and filter circuit (25), a transistor (27), a pulse width modulation circuit (26) outputting a control signal to control operation state of the transistor, and a feedback circuit (29). An external alternating current voltage is converted into a direct current with a cooperation operating of the transistor, the first commutating and filter circuit, the transformer, and the second commutating and filter circuit. The feedback circuit feeds an operating state of the transformer back to the pulse width modulation circuit, and the pulse width modulation circuit outputs corresponding control signals to turn on or turn off the transistor.