The drive electricity that MOSFET needs is smaller than BJT much, and normally OK and direct by CMOS or drive of circuit of drive of TTL of collector open a way; Next the switch rate of MOSFET is rapidder, can work with higher rate, because do not have charge memory effect; Additionally MOSFET does not have puncture failure mechanism 2 times, it is when temperature is higher often staying power is stronger, and the possibility that produces thermal breakdown is smaller, still can provide better performance inside wider temperature range. MOSFET had received a large number of application, in product of equipment of product of consumptive electron, industry, Electromechanical, smartphone and electron of other portable amount everywhere is seen.

   

In recent years, the industry that waits for product of many application MOSFET as industry of car, communication, the sources of energy, consumption, green is in got rapid development in last few years, power MOSFET is to get attention fully more. According to forecasting, 2010-2015 year the increase rate of overall and compound year of market of Chinese power MOSFET will be achieved 13.7% . The brilliant circle that although the market studies because macroscopical investment and economic policy are mixed,company ISuppli expresses,shake of day this locality brings and raw material supply a problem, the power MOSFET market this year can put delay, but the demand that consumes electron and data processing still exuberant, because this looks for a long time, the growth of power MOSFET or meeting comparative one paragraph continuously long time.

   

The technology is in all the time progress, power MOSFET market got gradually the challenge of new technology. For example, there are many companies to had begun parts of an apparatus of power of GaN of research and development inside course of study, and say or state with certainty the space that the function of silicon power MOSFET can promote is already special and limited. Nevertheless, gaN still is in very primary level to the challenge of power MOSFET market, MOSFET still holds clear dominant position in the respect such as technical maturity, supply, through development of more than 30 years, MOSFET market also won’t be replaced quickly by new technology easily.

   

Inside 5 years of longer even time, MOSFET still can hold the position of dominant. MOSFET also will still be numerous just met into the engineer of travel the parts of an apparatus of bring into contact with, this period half moon talks will begin from the foundation, discuss a few ABC of MOSFET, the introduction that includes type selecting, crucial parameter, system and come loose to consider hotly to wait a moment; Still can be everybody to make a few introductions with respect to a few the commonnest popular application finally.

   

The type selecting foundation of MOSFET

  

MOSFET has two big kinds: N raceway groove and P raceway groove. In power system, MOSFET can be regarded as electric switch. Should mix in the grid of MOSFET of N raceway groove when positive electricity is being added to press between source pole, its switch guides. Guide when connecting, electric current but classics switch from leakage extremely flow to source pole. Leakage pole is mixed an internal resistance exists between source pole, call guide electrify block RDS (ON) . The grid that must be clear about MOSFET is a tall impedance end, accordingly, always want to increase a tension in grid. If bar is very impending, general of parts of an apparatus cannot work by design intent, guide possibly in impertinent hour connect or shut, bring about a system to produce potential power loss. Should the voltage between source pole and grid is zero hour, switch is shut, and electric current stops to carry parts of an apparatus or appliance. Although at this moment parts of an apparatus has been shut, but still small electric current exists, this says for leakage current, namely IDSS.

   

Regard electrical system as medium main part, how does the engineer make right choice according to parameter? The article will discuss how to choose correct MOSFET through 4 paces.

   

1) the choice of raceway groove. The first situation that chooses correct parts of an apparatus for the design is to decide to use N raceway groove or MOSFET of P raceway groove. In typical power application, when ground connection of a MOSFET, and when laden join arrives on trunk voltage, this MOSFET made low-pressure side switch. In low-pressure side switch, should use MOSFET of N raceway groove, this is to stem from the consideration that connects place of parts of an apparatus to need voltage to shut or guiding. When MOSFET join arrives when bus line and laden ground connection, be about to use high-pressured side switch. MOSFET of P raceway groove is used in connecting regular meeting to attack in this develop, this also is the consideration that stems from pair of voltage drive.

 

  

2) the choice of voltage and electric current. Rated voltage is bigger, the cost of parts of an apparatus is higher. The basis carries out experience, rated voltage ought to be more than trunk voltage or total line voltage. Such ability provide adequate protection, make MOSFET won’t invalidation. With respect to choice MOSFET character, must decide leakage pole comes the likelihood between source pole susceptive is the biggest voltage, namely the biggest VDS. The other and safe element that design engineer needs to consider includes by switch electron equipment (like electric machinery or transformer) the voltage twinkling that cause changes. The rated tension that different applying also differs somewhat; Normally, portable equipment is 20~30V, 85~220VAC application to be 450~600V for power source of 20V, FPGA.

   

In guide continuously connect mode to fall, MOSFET is in stable state, right now electric current carries parts of an apparatus or appliance continuously. Pulse aiguille is to point to a large number of report emerge (or aiguille electric current) had shed parts of an apparatus. Once decided the biggest electric current below these conditions, need to choose to be able to bear directly only the parts of an apparatus of this the biggest electric current but.

   

3) computation guides a loss. The power consume of MOSFET parts of an apparatus but by Iload2×RDS (ON) computation, because guide electrify block changes along with temperature, because this power consume also is met,change in proportion subsequently. To portable design, it is easier to use inferior tension (relatively general) , and design to industry, can use taller tension. Notice RDS (ON) resistor is met as electric current slight rise. About RDS (ON) the technical data that all sorts of electric parameter change of resistor can provide in manufacturer is checked in the watch.

   

4) of computational system medicinal powder hot demand. Design personnel must consider two kinds of different cases, namely worst circumstance and true condition. The proposal uses the computational result that is aimed at worst circumstance, because this result offers larger safe surplus, can ensure system won’t invalidation. There still is what a few needs notice to measure data on the data table of MOSFET; Enclose the thermal resistance between the semiconductor knot of parts of an apparatus and environment for instance, and the biggest bear is lukewarm.

   

Switch loss also is a very main index actually. Can see from next graphs, guide the product of voltage electric current that understands the instant comparatives big. The switch function of parts of an apparatus decided on certain level. Nevertheless, if the system is right switch performance demand is higher, can choose grid charge QG to compare small power MOSFET.

 

  

MOSFET application case is analytic

  

1.    Switch power source applies

  

Go up from the definition and character, MOSFET of need of this kind of application guides regularly connect and close. In the meantime, 10 kinds of several develop attack can use at switch power source, here considers a simple case. The commonly used basic step-down converter in DC-DC power source relies on two MOSFET to execute switch function (next graphs) , these switch store in inductance alternately energy, give load energy release next. Current, design employee often chooses the frequency of hundreds KHz and even 1 MHz above, because frequency is taller, magnetic component is OK smaller lighter. The 2nd important MOSFET parameter in switch power source includes to output impedance of voltage of capacitance, threshold value, grid and avalanche energy.

 

  

2. motor controls application

  

The another application domain that motor control application is the land that power MOSFET has use force greatly. Circuit of typical half bridge-type control uses 2 MOSFET (complete bridge-type uses 4) , but of these two MOSFET pass time (dead band time) equal. To this kind of application, restore time reversely (Trr) very important. Controlling inductance type load (for instance motor winding) when, control circuit goes to the MOSFET switch in bridge-type circuit close position, the body diode with the right now medium MOSFET of another switch course in bridge-type circuit temporarily retrorse conduction current. Then, electric current circulates afresh, continue to be motor power supply. Guide again when the first MOSFET when connecting, the charge of the memory in another MOSFET diode must be moved to divide, pass discharge of the first MOSFET, and the loss that this is a kind of energy, reason Trr is shorter, this kind of loss is smaller.

   

3. car applies

  

In nearly 20 years of in the past, the car had gotten great progress with power MOSFET. Because its can be able to bear or endure,choosing power MOSFET is suffer what middling of car electron system encounters to drop carry and the appearance of systematic energy mutation transient state high pressure that cause, and its are enclosed simple, basically use TO220 and TO247 to enclose. In the meantime, rain of eject of electric car window, fuel, intermittent type is brushed and the application such as cruise control already became the mark of most car to match gradually, similar power parts of an apparatus needs in the design. During this, gain ground increasingly as electric machinery, solenoid and fuel ejector, the car also develops ceaselessly with power MOSFET expand.

   

The MOSFET parts of an apparatus that uses in automobile equipment is involved extensive voltage, electric current and guide electrify block limits. Electric machinery controls equipment bridge to receive configuration to be able to use 30V and model of 40V puncture voltage; And in must control load dash forward the circumstance of the circumstance of discharge and jump that start, can use load of 60V device drive; When occupation standard move comes when 42V batteries system, need to use 75V technology. The equipment of tall auxiliary voltage needs to use 100V to come 150V money; Apply at engine drive unit and tall brightness to discharge as to the MOSFET parts of an apparatus of 400V above (HID) the control circuit of headlight.

   

The limits of electric current of car MOSFET drive comes by 2A 100A above, guide the limits of electrify block comes for 2mΩ 100mΩ . The load of MOSFET includes electric machinery, valve, lamp, heat sex of component, capacitance controls electric component and DC/DC power supply. The limits of switch frequency comes for 10kHz normally 100kHz, what must notice is, electric machinery controls frequency of not applicable switch to be in 20kHz above. The main demand of other is UIS function, below node temperature limit (- 40 degrees reach 175 degrees, be as high as 200 to spend sometimes) working state, and the high reliability that surmounts car service life.

   

4.The drive of LED lamps and lanterns.

   

MOS pipe often should be used when designing LED lamps and lanterns, to drive of LED constant current character, use NMOS commonly. Power MOSFET and ambipolar model transistor is different, its grid electric capacity is larger, in guide before connecting, want to charge to this capacitance first, exceed threshold value voltage when capacitance voltage (VGS-TH) when MOSFET just begins to guide. Accordingly, ability of grid driver load must notice when the design must enough big, capacitance of quits effect grid is finished in order to assure inside the time that the system asks (CEI) charge.

   

And the switch speed of MOSFET inputs capacitance with its fill discharge to have very big concern. Although the person that use cannot reduce the cost of Cin, but the cost that can reduce Rs of internal resistance of source of signal of grid drive loop, reduce grid return thereby fill discharge time constant, accelerate switch rate ability of general IC drive basically is reflected here, we talk about choice MOSFET is IC of constant current of drive of MOSFET of the buy outside pointing to. Inside the IC of buy MOSFET of course need not we considered again, be more than MOSFET of the buy outside Lv of unified exam of 1A electric current commonly. To acquire bigger, more agile LED power capacity, buy MOSFET is only choice way outside, IC needs appropriate drive capability, MOSFET input capacitance is crucial parameter. Cgd laying a plan and Cgs are capacitance of MOSFET equivalent knot.

 

 

The PWM OUT output of general IC is in-house and compositive current limliting resistor, specific and numeric size outputs ability to concern with the peak value drive of IC, can think approximately R=Vcc/Ipeak. Rg of ability of drive of average band IC chooses to be controlled in 10-20Ω .

   

The drive of the IC in general application is OK and direct drive MOSFET, but considering normally drive takes a line is not linear, feeling quantity may bigger, and to prevent exterior interference, still want to use Rg drive resistor to undertake inhibition. Considering the effect that takes line distributinging electric capacity, this resistor should stand by the grid of MOSFET as far as possible.

 

  

Of above discussion is the choice of the resistor when MOSFET ON condition, to make sure grid charge is fast when MOSFET OFF condition have diarrhoea is put, right now block value wants as far as possible small. Put to assure fast have diarrhoea normally, OK on Rg shunt-wound a diode. When have diarrhoea discharge block passes small, because walk along the reason of line inductance to also can cause resonance (also can be in some application accordingly on this diode string together a little resistance) , but because the retrorse electric current of diode does not guide,connect, right now Rg participates in retrorse and syntonic loop again, because this can restrain the aiguille of retrorse resonance.

   

Estimation guides the requirement that understands loss, output and cement division temperature when, with respect to the method that can consult preamble place points out.

   

The applied field of MOSFET is very extensive, 9 articles can generalize far from. Welcome everybody to read the content related website more and link, the increasingly main effect that understanding MOSFET is producing now.