Electronic equipment must use direct current source, receive power source most those who be afraid of is negative pole is received turned over. If was not prevented,receive circuit instead, that does not know to be able to produce what situation, component damages that is affirmative. So general circuit can be added receive circuit instead, introduce a few kinds of commonly used circuit as follows.

 

1, use a diode to prevent receive circuit instead

Normally inputs of next direct current source prevent the circumstance to receive protective circuit instead is to use the one-way conductivity of diode to come true prevent receive protection instead. If the graph shows 1 times:

 

 

This kind receives a standard simple and reliable, cost is low, but influence of the power comsumption below the circumstance that should input big electric current is very big. If input voltaic rating to achieve 3A, general diode is pressed fall for 0.7V, so power comsumption also wants to achieve at least: 2.1W of ＝ of Pd ＝ 3A×0.7V, loss is so big, such efficiency are sure low, and calorific amount is large, want to add radiator. This does not delimit did not come. So this kind can be used in small electric current only, ask not tall circuit is medium.

 

2, use bridge-type commutate canal to do prevent receive circuit instead

Use diode bridge to do rectification to the input, such circuit have correct polarity forever. If pursue 2 circuit

 

 

The bridge-type commutator that 4 diode comprise, input power source to be being lost no matter how to receive, outputting polarity is normal. Principle and method 1 same, it is the only guide that uses diode epicene, but bridge-type commutate has two diode to guide at the same time, so power comsumption is a graph double of 1. When input electric current is 3A, 4.2W of ＝ of Pd ＝ 3A×0.7V×2, should add carbon fin more. This cost is higher, not practical.

 

The switch that used MOS pipe is characteristic, dominate circuit guide connect and disconnect will design prevent receive protective circuit instead, the internal resistance that provides as a result of power MOS is very little, now MOSFET Rds (On) can have accomplished fine long hair Europe class, solved existing use diode power source to prevent what receive plan existence instead to press fall to pass big question with power comsumption.

 

Polarity receives protection to will protect use effect instead canal and be established ties to join by protective circuit. Once be turned over to receive by the power source polarity of protective circuit, canal of protective use effect can form open circuit, the field effect in preventing circuit of voltaic burn down provides element, protect integral circuit.

 

MOS canal prevents N raceway groove to if pursue,receive protective circuit circuit instead 3 show

 

 

Canal of MOS of N raceway groove is strung together through S pin and D pin receive between power source and load, resistor R1 offers voltage to slant for MOS canal buy, use the switch character that MOS is in charge of to dominate circuit guide connect and disconnect, prevent power source to receive load to bring damage instead thereby. Receiving time, r1 offers VGS voltage, MOS saturation guides. When be being received instead, MOS cannot guide, rise to prevent so receive effect instead. The Rds that power MOS is in charge of (On) 20mΩ is only actual loss is very small, the electric current of 3A, power comsumption is (3×3)×0.02=0.18W uses adscititious carbon fin far from. Solved existing use diode power source to prevent what receive plan existence instead to press fall to pass big question with power comsumption. VZ1 prevents bar source voltage for stabilized voltage canal canal of exorbitant puncture Mos.

 

MOS canal prevents P raceway groove to if pursue,receive protective circuit circuit instead 4 show

 

 

What guide because of what NMOS is in charge of electrify block compares PMOS is small and the value is relative cheaper, had better choose NMOS.