Load open circuit detection circuit and LED driver having same

Abstract

The invention mainly provides a load open circuit detection circuit which is used for executing load open circuit detection on a constant-voltage LED driver, and the constant-voltage LED driver comprises a power-type MOS transistor and is coupled with an LED lamp. The load open circuit detection circuit basically comprises a microcontroller and a detection circuit unit. The detection circuit unit is coupled to a drain terminal of the power-type MOS transistor and the microcontroller. When the brightness of the LED lamp is larger than 0% and smaller than 100%, the detection circuit unit receives a detection signal transmitted by the microcontroller and receives an assembly output signal transmitted by the drain end of the power type MOS transistor at the same time, and therefore a sampling signal is generated according to the detection signal and the assembly output signal. After the sampling signal is received, the microcontroller performs at least one signal processing on the sampling signal so as to judge whether the load of the constant-voltage LED driver is in an open circuit or not according to the signal processing result.

Description

technical field [0001] The present invention relates to the technical field of electronic circuits, in particular to an open-load detection circuit used in an LED driver with a PWM dimming function. Background technique [0002] As we all know, Light-Emitting Diode (LED) is a widely used solid-state light-emitting component. It has the advantages of small size, energy saving and long service life, so it has been widely used in people's daily life. Fabrication of lighting fixtures. With the rapid development and application of LED lighting devices, commercially available LED lighting devices also further have a dimmable function. [0003] DALI, the full name of Digital Addressable Lighting Interface in English, and the full name of Digital Addressable Lighting Interface in Chinese, is an international dimming signal protocol applied to LED lighting devices. Powerful and other advantages. Therefore, the LED lighting device using DALI protocol for dimming control has good sc...

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Problems solved by technology

[0010] It should be added that the above-mentioned method of only taking the output current when the PWM signal is ON also has the problem of excessive power consumption of the current sampling resistor 12a

For a constant voltage LED driver 1a with an output voltage of 12V and an output power of 120 watts, the resistance value of the current sampling resistor 12a is 50mΩ, the power consumed by the load unit (that is, the LED lamp 2a) is 120 watts and the PWM When the output current when the signal is ON is 10A, the voltage drop across the current sampling resistor 12a is 500mV, causing the current sampling resistor 12a to consume 5 watts of power

On the other hand, when the power consumed by the load unit (that is, the LED lamp 2a) is 12 watts and the output current when the PWM signal is ON is 1A, the voltage drop across the current sampling resistor 12a is only There is 50mV, causing the current sampling resistor 12a to consume 50 milliwatts of power

It can be seen from the above description that considering the power consumption of the current sampling resistor 12a, the selection of the resistance value of the current sampling resistor 12a cannot make the constant voltage LED driver 1a of a single model specification take care of both the large wattage load and the small wattage load at the same time. , otherwise it will lead to misjudgment of load detection due to the power consumption of the current sampling resistor 12a

[0011] From the above description, it can be seen that there is still a lack of load open circuit detection scheme suitable for constant voltage LED drivers at this stage

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