Overvoltage protective circuit in LED driving power supply without auxiliary winding

Abstract

The invention provides an overvoltage protective circuit in an LED driving power supply without an auxiliary winding. A sampling and holding unit detects a voltage Vcs flowing through a current sampling resistor of the driving power supply; a time detection unit detects conduction time of a secondary side diode of the driving power supply, and the conduction time is utilized to generate a voltage Vref via a current source and a charging capacitor; when the conduction time of the secondary side diode ends, a first comparator compares the voltage Vref and the voltage Vcs, and when the voltage Vref is less than the voltage Vcs, the first comparator outputs an overvoltage signal to a control logic unit; the control logic unit outputs a switching signal to a switching driving unit according to the overvoltage signal; and the switching driving unit turns off a power tube of the driving power supply according to the received switching signal. An independent transformer winding is not needed in detection of the output voltage, and detection of a pin bit is also not needed so that the manufactured LED driving power supply is smaller in volume and lower in cost.

Description

technical field [0001] The invention relates to the technical field of LED overvoltage protection, and more specifically relates to an overvoltage protection circuit in an LED driving power supply without auxiliary windings. Background technique [0002] With the continuous development of electronic technology, the application range of LED lights is becoming wider and wider. The working principle of the LED lamp is to provide a constant output current through the LED drive power supply to light the LED lamp. Therefore, when the output LED is open circuit or other circumstances make the output voltage higher, the LED drive power supply must take corresponding measures to keep the output voltage not exceeding the withstand voltage of the output capacitor, otherwise the output capacitor will be easily burned out. In the traditional LED drive power supply, a separate transformer winding is generally used to detect the output voltage, and then divided by resistors, input to a se...

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Problems solved by technology

[0004] It can be seen from this that the traditional LED overvoltage protection scheme increases the volume and cost of the entire LED drive power supply. In order to detect the overvoltage point, it is necessary to add a transformer winding, two voltage divider resistors, and one more chip. Detecting the pin position is not suitable for the development trend of small size and low cost of LED in the current market

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