I. Application Scope of MOS Switching Power Supply

Switching power supply applications, by definition, require regular turn-on and turn-off of MOSFETs. At the same time, there are dozens of topologies that can be used in switching power supply. Consider a simple example here. The basic step-down converters commonly used in DC-DC power supply rely on two MOSFETs to perform switching functions (figure below), which alternately store energy in inductors and then release energy to the load. At present, designers often choose frequencies of hundreds of kHz or even more than 1 MHz. Because of the higher frequencies, magnetic components can be smaller and lighter. The second important parameters of MOSFET in switching power supply include output capacitance, threshold voltage, gate impedance and avalanche energy.

II. Application Range of MOS Motor Controller

Motor control application motor control application is another application field of power MOSFET. Typical half-bridge control circuits use two MOSFETs (full-bridge control uses four), but the turn-off time (dead-time) of the two MOSFETs is equal. For such applications, reverse recovery time (trr) is very important. When controlling inductance loads (such as motor windings), the control circuit switches the MOSFET in the bridge circuit to the turn-off state, at which time another switch in the bridge circuit temporarily conducts the current through the body diode in the MOSFET. Thus, the current is recycled to continue to power the motor. When a MOSFET is turned on again, the charge stored in another MOSFET diode must be removed and discharged through a MOSFET, which is a loss of energy, so the shorter the trr, the smaller the loss.

三、MOS管汽车行业应用范围III. Application Scope of MOS Tube in Automotive Industry

The power MOSFET is chosen because it can withstand the transient high voltage phenomenon caused by load drop and system energy mutation in automotive electronic system, and its packaging is simple, mainly using TO220 and TO247 packages. At the same time, the application of electric windows, fuel injection, intermittent wipers and cruise control has gradually become the standard of most automobiles, and similar power devices are needed in the design. During this period, with the increasing popularity of motors, solenoids and fuel injectors, vehicle power MOSFET has also been growing. MOSFET devices used in automotive equipment involve a wide range of voltage, current and on-resistance. The bridge configuration of motor control equipment will use 30V and 40V breakdown voltage models, while 60V devices will be used to drive loads when sudden load unloading and sudden start-up must be controlled, and 75V technology will be used when industry standard is transferred to 42V battery system. The driving current range of automotive MOSFET is from 2A to 100A, and the on-resistance range is from 2m_to 100m_. The loads of MOSFET include motors, valves, lamps, heating components, capacitive piezoelectric components and DC/DC power supply. The switching frequency range is usually 10 kHz to 100 kHz. It must be noted that motor control is not suitable for switching frequency above 20 kHz. Other major requirements are UIS performance, working conditions at junction temperature limits (- 40 to 175 degrees, sometimes up to 200 degrees), and high reliability beyond vehicle life.

IV. Application Scope of MOS LED Driver

LED lamp driver. MOS transistors are often used in the design of LED lamps. NMOS is generally used for constant current drive of LED. Power MOSFET is different from bipolar transistors in that its gate capacitance is relatively large. The capacitor must be charged before it is turned on. When the capacitor voltage exceeds the threshold voltage (VGS-TH), the MOSFET starts to turn on. Therefore, it must be noted that the load capacity of the gate driver must be large enough to ensure that the equivalent gate capacitance (CEI) is charged within the required time of the system. The switching speed of MOSFET is closely related to the charging and discharging of its input capacitance. Although the user can not reduce the value of Cin, but can reduce the value of internal resistance Rs of the gate drive circuit signal source, thereby reducing the charge and discharge time constant of the gate circuit, accelerating the switching speed of general IC drive ability is mainly embodied here, we talk about the choice of MOSFET is the external MOSFET drive constant current IC. Of course, IC with built-in MOSFET need not be considered. Generally, the external MOSFET will be considered when the current is larger than 1A. In order to obtain larger and more flexible power capability of LED, the external MOSFET is the only choice. IC needs appropriate driving capability, and the input capacitance of MOSFET is the key parameter.