Various MOS tube Introduction

MoS Tube Learning

in the actual project, we basically use the enhanced MOS tube, divided into N-channel and P-Channel two kinds.

We often use nmos because of its low on-resistance and easy to manufacture. As can be seen on the MOS schematic, there is a parasitic diode between the drain electrode and the source. This is called a body diode, which is important in driving inductive loads such as motors. Incidentally, the body diode exists only in a single MOS tube, which is usually not available inside the IC chip.

1. Conduction characteristics

nMOS characteristics, VGs greater than a certain value will be conductive, suitable for use in the case of source grounding (low-end drive), as long as the gate voltage of 4V or 10V can be.
PMOs characteristics, VGs less than a certain value will be conductive, suitable for use when the source of VCC (high-end drive). However, although PMOs can be easily used as a high-end driver, the NMOS is usually used in high-end drives, due to the large on-resistance, the price, and the small number of replacements. 2.MOS Switch Tube loss

Whether it is nMOS or PMOs, there is a conduction resistor after conduction, so that the current will consume energy on the resistor, and this portion of the energy consumed is called conduction loss. Selecting a MOS tube with a low on-resistance will reduce the conduction loss. The current low-power MOS-tube resistance is generally around dozens of milli-euro, a few milli-European also have.
MOS must not be completed in an instant when it is on and off. The voltage at both ends of the MoS has a descent process, the flow of current has a rising process, during this time, the loss of the MoS tube is the product of voltage and current, called the switching loss. Usually the switching loss is much larger than the conduction loss, and the higher the switching frequency, the greater the loss.
The product of the instantaneous voltage and current is very large, resulting in a large loss. Shorten the switching time, can reduce the loss of each conduction, reduce the switching frequency, can reduce the number of switches per unit time. Both of these methods can reduce the switching loss. 3.MOS Tube Drive

Compared with bipolar transistors, it is generally believed that the MoS tube conduction does not require current, as long as the GS voltage above a certain value, it can be. This is easy to do, but we still need speed.
In the MOS tube structure can be seen, there is a parasitic capacitance between the GS,GD, and the MoS Tube driver is actually the charge and discharge of the capacitor. The charge of the capacitor requires a current, because the capacitor can be charged instantaneously as a short circuit, so the instantaneous current will be relatively large. When selecting/Designing the MoS Tube driver, the first note is that the instantaneous short-circuit current can be supplied in size.
The second note is that the commonly used nmos for high-end drives requires a gate voltage greater than the source voltage at the conduction time. While the high-end driver MOS transistor is on, the source voltage is the same as the drain voltage (VCC), so the gate voltage is 4V or 10V larger than VCC. If you are in the same system, to get a higher voltage than VCC, you need a special boost circuit. Many motor drivers are integrated with charge pumps, it should be noted that the appropriate external capacitor should be selected to obtain sufficient short-circuit current to drive the MoS tube. 4. Enhanced and depleted type Mos-fet

We often use enhanced mos-fet.

Enhanced Mos-fet in the case of the gate without voltage is turned off, only when the VGS meet the opening conditions will form a conductive channel, will lead.
Depletion type Mos-fet in the case of the gate without voltage is open, only when the VGS meet the shutdown conditions when the conductive channel will be clamped.
5. Junction type and insulated gate type field effect Tube

1, the Insulation gate type field effect Tube Gate is easy to breakdown damage , so in the packaging on the insulation gate-type long-lasting pipe pin between the short-circuit or with metal foil wrapped. The junction-type FET is not required on the packaging.

2, the Insulation gate type field effect Tube G, s at both ends of the positive and reverse resistance values are very large almost non-conductive, the junction of the field-effect tube g, S end resistance value of the PN junction positive, reverse resistance. Can be judged by the resistor file of the multimeter.

3, Insulated Gate Type field effect tube is more commonly used, because of its high input impedance.