Today, I tangled when you see a circuit diagram for a long time, circuit is as follows:
When I saw this MOS transistor feeling, not ah this is not a direct DS is conducting Well, it is not above BAT power supply directly to the VDD Well, how power switching can do it. This diagram does not completely good interpretation of what the power switch,, because I look at it the whole circuit diagram after its first issue this is and 12V power supply VDD is actually linked together, which explains, even if you MOS tube is a path, as long as I did not break current 12V, electric BAT your battery will not work. Then there was the god of the improved circuit. Circuit is as follows:
The MOS transistor in turn connected, so that very clear to see, the DS is not turned on, VOUT is temporarily no current. When the 12V power supply is turned on, VG> VS MOS transistor is not conducting, when the 12V power is off, VG <VS (VGS = -3.3V ) MOG conducting tube. VOUT = BAT is a battery voltage. Have to say this time, the pressure of such a big VG and VS, the MOS transistor will breakdown, and this time they can improve the look of the circuit, the circuit diagram as follows:
At this time, we add a transistor, and B two parallel pre-voltage-dividing resistors, to prevent damage to the transistor, the normal manual to understand the need to look at the data between the maximum voltage UBE how much the voltage UB control pressure within its scope. Subsequently, when the voltage of 12V is turned UB> U3 voltage is not turned on, when 12V is disconnected, UE> UB after the conduction, UG R2 through voltage is less than the partial pressure of the US MOS transistor is turned on, VOUT = BAT cells Voltage,
