PMOs Tube Learning Application

http://blog.csdn.net/wang_xuehen/article/details/7895301

First of all, the application of their own background to do a description, I do a system in the power supply part needs two battery switching power supply, so to do an electronic switch, this switch should be as low as possible electricity consumption. General use of electronic switches can be selected transistor, but the transistor voltage drop and leakage current is not acceptable to the system. So it is necessary to use the MoS tube, its on-off pressure drop, generally in the Hao-level, the resistance in the Hundred euro level (for example, 117 mm), so that the switch in the open after the pressure drop will not be too large, close the leakage will not be too large, to meet the application.

The mold electricity is not very good, the MOS tube knowledge basically also has returned the teacher. can only search information from the Internet, look again. I experiment with the pipe is irf9540n, the original thought suffix with n should be n ditch, no Chengxiang this pipe is P ditch. A description of the P-channel reinforced MOS tube:

The PMOs feature is that when the value of the VGS is less than a certain value, the tube will be conductive, which is suitable for the source-connected VCC. The following is an enhanced PMOs working characteristic curve:

It is shown from the figure that the larger the VGS, the greater the allowable drain current. Pipe work consists of four zones: variable resistance zone, constant current zone, breakdown zone, cutoff area, as shown in the following figure:

The constant current zone is also called the saturation zone, and the pipe works in this area. There are two graphs to indicate that when the absolute value of the VGS is higher than 4V, the pipe cutoff, below this value, the pipe conduction. The threshold value of the irf9540n is between -2~-4 and the VGS is only higher than the 4V tube. But I do the system in the power supply voltage below 4V, so this pipe is actually not available.

Attach the circuit diagram of the electronic switch:

When 5V power supply, the VGS absolute value is higher than 4V, the pipe cutoff, after continuous discharge, when its voltage drops below 4V, the pipe conduction, battery bat work. The following two resistors can determine the voltage at both ends of the VGS.