Driving circuit for directly supplying power to LED lamp tube by adopting power adapter and design method

Abstract

The invention relates to a driving circuit for directly supplying power to an LED lamp tube by adopting a power adapter. The power adapter is electrically connected with a 220V commercial alternatingcurrent and an LED lamp tube. The LED lamp tube is electrically connected with the drain end of an N-channel MOS tube Q1. The source end of the N-channel MOS tube Q1 is grounded through a current sampling resistor R1. The grid end of the N-channel MOS tube Q1 is electrically connected with the output end of an operational amplifier OP through a resistor R2. Two ends of a parasitic capacitor Cgd inthe N-channel MOS tube Q1 are electrically connected with one end of a current sampling resistor R1 and one end of a resistor R2 respectively. The grounding end of the operational amplifier OP is grounded. The power supply end of the operational amplifier OP is electrically connected with the output end of the power adapter through a Vcc power supply control circuit. The Vcc power supply controlcircuit receives an On / off switch signal of the mainboard. The negative input end of the operational amplifier OP is electrically connected with one end of the current sampling resistor R1. The positive input end of the operational amplifier OP is electrically connected with one end of a resistor R3 and one end of a resistor R4. The other end of the resistor R3 is grounded, the other end of the resistor R4 is electrically connected with reference voltage Vref, and the positive input end of the operational amplifier OP receives PWM dimming signals of the mainboard.

Description

technical field [0001] The invention relates to the technical field of liquid crystal display devices, in particular to a driving circuit for directly supplying power to an LED lamp tube by a power adapter and a design method for the LED lamp tube. Background technique [0002] At present, for liquid crystal display products powered by an external power adapter, the internal LED lamp drive circuit usually uses such as figure 1 The traditional Boost boost LED tube drive circuit shown in the figure uses a power adapter to output such as: 19V DC voltage must be boosted by the Boost boost LED tube drive circuit before being provided to the LED tube to work. 1. Traditional If the Boost LED lamp drive circuit adopts PWM dimming and the dimming frequency is too high, such as: the dimming frequency is greater than 20KHZ, it will cause the following problems: ①When the LCD screen is bright, the PWM dimming duty cycle ( Duty) is relatively large, and the entire Boost LED lamp drive c...

AI Technical Summary

Problems solved by technology

[0002] At present, for liquid crystal display products powered by an external power adapter, the internal LED lamp drive circuit usually uses such as figure 1 The traditional Boost boost LED tube drive circuit shown in the figure uses a power adapter to output such as: 19V DC voltage must be boosted by the Boost boost LED tube drive circuit before being provided to the LED tube to work. 1. Traditional If the Boost LED lamp drive circuit adopts PWM dimming and the dimming frequency is too high, such as: the dimming frequency is greater than 20KHZ, it will cause the following problems: ①When the LCD screen is bright, the PWM dimming duty cycle ( Duty) is relatively large, and the entire Boost LED lamp drive circuit system is prone to instability problems due to too high PWM operating frequency. ②When the LCD screen is low, the PWM dimming duty ratio (Duty) is relatively small, which may cause Because the Boost boost LED tube driver circuit in each PWM dimming cycle, the working cycle time of the boost MOS tube Q1 is less than the delay time (delay time) of the internal protection circuit of the LED tube drive control chip, resulting in light inside the LED tube When the diode is abnormally short-circuited or open-circuited, the LED lamp drive control chip cannot perform normal protection actions. Therefore, the PWM dimming frequency of the traditional Boost LED lamp drive circuit that uses PWM dimming is usually set at 180HZ-300HZ or so, but the traditional Boost LED lamp driver adopts low-frequency PWM dimming, which has the following disadvantages: ①Boost boost inductor L1 is prone to abnormal sound problems (audio range received by the human ear: 20HZ-20KHZ), ②Low frequency PWM dimming is prone to image water ripple interference or picture flickering

[0003] 2. In the traditional Boost LED lamp drive circuit, Q1 MOS tube, L1 Boost boost inductor, and D1 boost diode are easy to produce high-frequency EMI electromagnetic radiation problems when they are working, which makes some liquid crystals When new models of monitors are tested for EMI, the EMI radiation margin is insufficient or exceeds the regulatory standards, which requires a lot of manpower and time to solve and improve, which may eventually lead to increased product design costs and a small number of products that cannot be put on the market in time And other issues

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