MOS transistor switching circuit design knowledge oled module

1, MOS tube type and structure
FET is the MOSFET (the other one is JFET), may be manufactured or enhanced depletion type , P -channel or N-channel type of four kinds , but the practical application of only N -channel enhancement type MOS tubes and P -channel enhancement type MOS transistor , it is usually referred to NMOS, PMOS , or refers to two .

For both enhanced MOS, more commonly used is NMOS. The reason is that the on-resistance is small, and easy to manufacture . Therefore, the switching power supply and motor drive applications, typically using NMOS. The following presentation, also mostly NMOS based.
Parasitic capacitance exists between the three pins MOS transistor , which is not what we need, but because of the manufacturing process limitations arising . Parasitic capacitance makes the design or selection of the drive circuit will take some time , but there is no way to avoid back again in detail.
MOS tube can be seen on the schematic , there is a parasitic diode between the drain and the source . This is called the body diode , drive inductive loads ( such as motors ) ,Tsingtek lcd graphic display this diode is very important. Incidentally , only the body diode of the MOS transistor in the presence of a single , integrated circuit chip is usually not .
2, MOS conduction characteristics
A conduction switch means is equivalent to a closed switch .
The characteristics of NMOS , Vgs greater than a certain value becomes conductive , suitable for the case when the source is grounded ( low side driver ) , as long as the gate voltage reaches 10V 4V or on it.
Characteristics of the PMOS , Vgs less than a certain value is turned on, the situation is extremely suitable for the source when connected to VCC ( high drive ) . However, while the PMOS can be conveniently used as high-side driver , but the on- resistance is large , expensive, and less replacement types reasons, the high-side driver , it is usually used NMOS.
3, MOS switch losses
Regardless of the NMOS or PMOS, both the on-resistance conduction exists, so current will dissipate energy in this resistor, which is called the partial consumption of energy conduction losses . Choose a small on-resistance MOS tube reduces conduction losses. Now a small on-resistance power MOS usually around tens of milliohms , there are a few milliohms .
MOS is turned on and when the cut-off , certainly not instantaneous. There is a voltage drop across the MOS process , there is a current flowing in the process of rising , at this time, the loss of MOS tube is the product of voltage and current , called switching losses. Switching losses are usually much larger than the conduction losses and switching frequency , the faster , the greater the loss .
Conducting product of the instantaneous voltage and current is large, will cause great damage . Shorten the switching time ,Tsingtek Character OLED Display conduction loss can be reduced every time ; reduce the switching frequency , the switching frequency can be reduced per unit of time . Both approaches can reduce the switching losses.