LED Power Supply Soft-Start Circuit for Overshoot-Free Switching
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Solution Overview
Problem
LED power supplies often experience large output current overshoots during continuous on/off switching, which can damage LEDs and reduce their lifespan.
Innovation Solution
A continuous on/off circuit without overshoot is designed, incorporating a voltage divider circuit, optocouplers, MOS transistors, and operational amplifiers to softly start the power supply during switching, preventing current overshoots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the LED power supply is switched on and off continuously, then the power supply can be controlled to turn on and off, but large output current overshoot occurs which damages the LED
Solution Approach 1:
The circuit performs preliminary action by pre-charging the output capacitor through a controlled path before the main power switch closes. The voltage divider circuit and auxiliary transistor Q2 activate first to charge capacitor C2, which then supplies current to pre-charge the output capacitor when Q1 turns on, preventing the sudden current surge that would otherwise damage the LED.
Solution Approach 2:
The patent introduces intermediary elements including the auxiliary transistor Q2, capacitor C2, and diode D3 that mediate between the power input and the LED load. These intermediaries create a controlled current path that limits and shapes the inrush current, preventing direct connection of the full power supply voltage to the LED and thus avoiding current overshoot.
2Speed
If the power supply switches on quickly, then the response time is fast, but the impact current pollutes the power grid
Solution Approach 1:
The circuit implements periodic action through the controlled charging and discharging cycles of capacitor C2. During each power-on event, C2 charges through the voltage divider and discharges through the MOSFET Q1 to pre-charge the output, creating a periodic current pattern that is gentler on the power grid while maintaining fast startup performance.
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 circuit effectively prevents current overshoots during continuous power switching, reducing the risk of LED damage, minimizing power grid pollution, and ensuring a longer LED lifespan.
Implementation Method 1
the voltage reference chip U5 is connected to the light-emitting end of the optocoupler U3, and the light-emitting end of the optocoupler U3 is also Input the first voltage, the conduction terminal of the optocoupler U3 is grounded through the resistor R3, and is also connected to the gate of the MOS transistor Q1
Implementation Method 2
the other light-emitting end is connected to the output end of the op amp U4, the conduction end of the optocoupler U2 is grounded, and the other conduction The terminal is connected to the driver chip U1 through the resistor R1
Implementation Method 3
the charging capacitor C2 is also grounded through the MOS transistor Q1
Implementation Method 4
A voltage divider circuit, which is connected to the input end, and is provided with a voltage reference chip U5 on its output end
Data Source
AI summary
A continuous switching machine without overshoot circuit, including an input terminal; a voltage dividing circuit; a voltage reference chip U5, the voltage reference chip U5 is connected to an optocoupler U3, and the optocoupler U3 also inputs a first voltage, and the optocoupler U3 is grounded through a resistor R3, It is also connected to the gate of MOS transistor Q1, and the second voltage is input through resistor R2; the second voltage is connected to optocoupler U2 through resistor R4, which is also connected to the output terminal of operational amplifier U4, and one end of optocoupler U2 Grounded, one end is connected to the driver chip U1 through the resistor R1; it also includes the third voltage, the third voltage is grounded through the resistor R8 and the charging capacitor C2, and is also connected to the positive phase terminal of the operational amplifier U4, and the charging capacitor C2 is also passed through the MOS transistor Q1 Grounding; the lamp terminal is grounded through the sampling resistor R_CS, and also connected to the negative phase terminal of the operational amplifier U4 through the resistor R12.