Driving circuit and circuit system thereof

A driving circuit has a current source, a first NMOS transistor, a second NMOS transistor, a resistor and a PNP bipolar junction transistor. A drain of first NMOS transistor receives a current with a positive temperature coefficient which is provided by the current source, and a gate of the first NMOS transistor is electrically connected to the drain of the first NMOS transistor. A gate of the second NMOS transistor is electrically connected to the drain of the first NMOS transistor. A drain and a source of the second NMOS transistor respectively receive an input voltage and generate an output voltage for driving a load. The two ends of the resistor are respectively electrically connected to a source of the first NMOS transistor and an emitter of the PNP bipolar junction transistor. A base of the PNP bipolar junction transistor is electrically connected to a source of the second NMOS transistor, and a collector of the PNP bipolar junction transistor is electrically connected to a low voltage. By selecting the