Switching Power Supply Protection Circuit for Optocoupler Failure
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Solution Overview
Problem
The failure of an optocoupler in conventional switching power supply circuits leads to ineffective voltage feedback, causing the supply voltage to exceed the withstand voltage of components and resulting in circuit damage.
Innovation Solution
A switching power supply protection circuit comprising a protection circuit, a switching circuit, a voltage feedback circuit, and a control circuit, which includes a protection chip, voltage-dividing circuit, switching tube, and optocoupler, to regulate the supply voltage and prevent excessive output voltage by controlling the switching circuit based on feedback voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional switching power supply circuits rely only on optocouplers for output feedback, then the circuit structure is simple, but when the optocoupler fails the chip cannot receive effective feedback signals and the supply voltage exceeds component withstand voltage causing circuit damage
Solution Approach 1:
The feedback function is segmented into two independent paths: the primary optocoupler feedback path and the secondary protection feedback path through the voltage-dividing circuit. When one path fails, the other can still provide feedback to prevent overvoltage damage.
Solution Approach 2:
The voltage-dividing circuit is pre-configured as a protective measure against optocoupler failure. This circuit provides a backup feedback path that activates when the primary optocoupler fails, cushioning against potential overvoltage damage before it occurs.
2Loss of information
If the optocoupler fails to provide effective feedback, then the feedback signal is lost, but the supply voltage rises to tens of volts exceeding component withstand voltage
Solution Approach 1:
The voltage-dividing circuit acts as an intermediary feedback path that mediates between the output voltage and the control chip. When the optocoupler fails, this intermediary circuit provides alternative feedback to prevent overvoltage, bridging the gap in the feedback mechanism.
Solution Approach 2:
The voltage-dividing circuit establishes an additional feedback loop that continuously monitors the output voltage and provides feedback to the control chip. This ensures that even when the optocoupler fails, the feedback mechanism remains active to prevent overvoltage conditions.
3Reliability
If a voltage-dividing circuit with Zener diode is added to provide backup feedback, then the protection capability is improved, but the device complexity increases
Solution Approach 1:
The voltage-dividing circuit serves multiple functions: it provides backup feedback when the optocoupler fails, limits voltage through the Zener diode, and works in conjunction with the primary feedback path during normal operation. This multi-functionality justifies the added components by providing comprehensive protection.
Data Source
AI summary
A switching power supply protection circuit includes a protection circuit, a switching circuit, a voltage feedback circuit, and a control circuit. The protection circuit is connected to the switching circuit, the voltage feedback circuit, and the control circuit, and controls output switch-on or output switch-off, controls switch-on or switch-off of the switching circuit, and controls the supply voltage. The switching circuit is connected to the control circuit and controls a working state of the control circuit. The voltage feedback circuit is connected to the control circuit and adjusts a control voltage and transmits the feedback voltage to the protection circuit. The control circuit is connected to a power supply and receives a voltage of the power supply for charging, provides a starting voltage for the protection circuit and controls the supply voltage according to the control voltage.