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.