The push-pull circuit consists of two MOS tubes, an N-channel MOS tube and a P-channel MOS tube. The two MOS tubes are connected together to form a push-pull structure. When working, when the input signal is high, the N-channel MOS tube is turned on and the P-channel MOS tube is turned off; when the input signal is low, the N-channel MOS tube is turned off and the P-channel MOS tube is turned on. In this way, the MOS push-pull circuit can achieve the function of signal amplification and load driving.

The push-pull circuit converts the input signal into the output signal through the alternating operation of two complementary MOS tubes, where one MOS tube acts as a load tube, responsible for outputting the current, and the other MOS tube acts as a driver tube, responsible for controlling the direction of the output current.

 The push-pull circuit is used to solve the problem of insufficient driving ability of the MOS tube and the limitation of the MOS tube characteristics .

So why do we need to consider the current size when using a push-pull circuit in a MOS tube?

First, when the current of some ICs or CPUs is small and the driving ability of MOS tubes is insufficient , the push-pull circuit can effectively increase the driving ability by using a pair of transistors to conduct in turn, thereby amplifying the current.

 In addition, the characteristics of the MOS tube must also be considered. Although the MOS tube is a voltage-controlled device, its turn-on and turn-off speeds are easily affected by the input capacitance. When the drive current is small, the charging and discharging speeds of the input capacitances CGS (C2) and CGD (C1) of the MOS tube will become slower. At this time, the push-pull circuit can directly bypass the limitations of the MOS tube and improve the response speed and efficiency of the circuit.

In order to ensure that the MOS tube can work safely and efficiently in the push-pull circuit, when designing the push-pull circuit, it is necessary to perform accurate current calculation and circuit design based on factors such as the maximum continuous drain current (ID), maximum power dissipation (PD) and gate-source voltage range (VGS) of the MOS tube.

Therefore, when using a push-pull circuit, the MOS tube considers the current size to ensure the stability and reliability of the circuit.