MOSFET and IGBT internal composition are different, those who decided its use a field is different

 

1, the structure as a result of MOSFET, normally it can accomplish electric current very big, can arrive on KA, but premise compression capability is strong without IGBT.

 

2, IGBT can be done very high-power, electric current and voltage are OK, it is a bit frequency not be too tall, at present speed of IGBT hard switch can arrive 100KHZ, that has been pretty good. Opposite nevertheless the working frequency at MOSFET or a drop in the sea, MOSFET can work hundreds of KHZ, go up MHZ, down to a few MHZ, the product of radio frequency domain.

 

3, apply with respect to its, according to its characteristic: MOSFET application heats at switch power source, ballast, high frequency induction, power source of welder of high frequency inversion, communication waits domain of high frequency power source a moment; IGBT applies at welder centrally, inverter, transducer, eletroplate electroanalysis power source, supersonic frequency induction heats wait for a domain.

 

Switch power source (Switch Mode Power Supply; The function of SMPS) relies on the choice of power semiconductor device greatly, namely switch canal and commutator.

 

Although do not have the plan of perfect to solve the problem that chooses IGBT or MOSFET, but the IGBT in applying in the light of specific SMPS and MOSFET undertake function is compared, the scope that defines crucial parameter still can have certain referenced effect.

 

The article will undertake discussing to a few parameter, like hard switch and soft switch ZVS (0 voltage are changed) develop attacks medium switch loss, right — of circuit and loss of switch of 3 parts of an apparatus is characteristic and relevant main power guides a loss, conduct loss and close loss to have a description. In addition, returning those who pass illustrate diode to restore character is to decide MOSFET or IGBT guide the main factor that knows switch loss, discussion diode restores the influence that function attacks to hard switch develop.

 

Guide a loss

 

The voltage decay time besides IGBT is longer outside, of IGBT and power MOSFET guide ten classification are like a character. By basic IGBT equivalent circuit (see a picture 1) can see, adjust completely the minority of area of base of PNP BJT collector carries stream child needs time was brought about guide electrify pressing pulls end (Voltage Tail) appear.

 

 

This kind of defer caused kind of saturation (Quasi-saturation) effect, make collector / blast off extremely voltage cannot drop to be worth to its VCE(sat) instantly. This kind of effect also was brought about fall in ZVS circumstance, in the retrorse paralell connection that load current encloses from combination diode changes the instant of the collector of IGBT, VCE voltage can rise. The time that the listed Eon specific power consumption in book of IGBT product standards is Icollector of each changeover cycle and VCE product is integral, the unit is joule, included with kind saturated and relevant other loss. Its are divided again for parameter of two Eon energy, eon1 and Eon2. Eon1 is to did not include to recover loss with hard switch diode the power loss of relevant specific power consumption; Eon2 included to restore relevant hard switch to guide with diode a specific power consumption, the diode with the identical diode that can enclose through restoring to be combined with IGBT will measure, if the graph is shown 2 times,typical Eon2 tests circuit. IGBT undertakes through two pulse switch changeover will measure Eon. The first pulse will increase inductance electric current to send needs test electricity in order to amount to, next the Eon loss that the 2nd pulse can measure test electric current to restore on diode.

 

 

Guide in hard switch the case that open falls, the refreshment of grid driving voltage and impedance and rectification diode is characteristic decided Eon switch loss. For circuit of PFC of step up of traditional to resembling CCM, step up diode restores character to guide in Eon () in the control of specific power consumption very important. Besides the step up diode that has the smallest Trr and QRR besides the choice, ensure this diode is had soft it is very important also to restore character. Bate is spent (Softness) , namely Tb/ta rate, the electric noise that produces to switch parts of an apparatus and voltage pointed pulse (Voltage Spike) has the effect that comparative. Diode of certain high speed is inside time Tb, the electricity that begins from IRM(REC) drops rate (Di/dt) is very tall, reason can produce tall voltage pointed pulse in circuit parasitism inductance. These voltage pointed pulse can cause electromagnetism to disturb (EMI) , exorbitant retrorse tension is caused possibly on diode.

 

In hard switch circuit, in attacking like complete bridge and half bridge develop, what with IGBT combination encloses is fast restore canal or MOSFET body diode, when corresponding switch the canal guides the diode when connecting has voltaic course, the refreshment of diode is consequently characteristic decided Eon loss. So, the MOSFET that chooses to have quick style diode to restore character is very important. Unfortunate is, the refreshment of the parasitism diode of MOSFET or body diode is characteristic the schism diode that uses at present than industry wants slow. Accordingly, to application of hard switch MOSFET, body diode often decides the limitative element of SMPS job frequency.

 

Generally speaking, the choice that IGBT combination encloses diode wants to match with its application, have inferior to what conduct loss slower model exceed fast diode and IGBT of slower drive of low VCE(sat) electric machinery combination is enclosed together. Contrarily, soft restore to exceed fast diode, can enclose together with combination of IGBT of mode of switch of high frequency SMPS2.

 

Besides choosing correct diode, design personnel still can be passed adjust grid drive guides the impedance that know a cause will control Eon loss. Reduce drive source impedance to guide those who raise IGBT or MOSFET a Di/dt and reduce Eon loss. Eon loss and EMI need are eclectic, because taller Di/dt can bring about voltage needle,pulse, radiate is mixed conduct EMI to increase. Understand the requirement of Di/dt to choose correct grid drive impedance to guide in order to satisfy, the likelihood needs to undertake circuit interior test and test and verify, can decide according to MOSFET changeover curve next probably value (3) seeing a picture.

 

 

Assume in guide when connecting, FET electric current rises to 10A, the basis pursues 3 in that curve of 25 ℃ , to reach the value of 10A, grid voltage must change 6.7V from 5.2V, average GFS is 10A/(6.7V-5.2V)=6.7mΩ .

 

 

Formulary 1 obtain place to need to guide the grid drive impedance that connects Di/dt

 

Use average GFS value to formula 1 in, get Vdrive=10V of grid driving voltage, needs Di/dt=600A/μs, FCP11N60 model is worth VGS(avg)=6V, ciss=1200pF; Can calculate then piece guide impedance is a grid drive 37Ω . Because in the graph GFS of the transient state in the curve of 3 is worth,be a diagonal, can appear during Eon change, mean Di/dt to also can change. The Vdrive of grid drive electric current that shows exponential attenuation and descendent Ciss also entered this formula as the function of VGS, expression has the overall effect that surprising linear electric current rises.

 

Same, IGBT also can undertake similar grid drive guides an impedance computation, VGE(avg) and GFS can pass the changeover character curve of IGBT to decide, apply the CIES value below VGE(avg) to replace Ciss. The IGBT of computational earning guides impedance is a grid drive 100Ω , this cost is higher than the 37Ω in front, show IGBT GFS is taller, and CIES is inferior. The crucial part here depends on, to change IGBT from MOSFET, must undertake modulatory to grid drive circuit.

 

Conduct loss to want discretion

 

When comparing rating to be the parts of an apparatus of 600V, the conduction of IGBT the 600 V MOSFET that loss compares same chip size commonly is little. This kind should be quite in collector and leakage extremely current density can feel apparently measure, and next the working written guarantee that in demonstrate the poorest condition issues is lukewarm undertaking. For example, FGP20N6S2 SMPS2 IGBT and FCP11N60 SuperFET all have 1 ℃ / the RθJC value of W. Graph 4 showed next conduction the knot in 125 ℃ is lukewarm the relation of loss and dc electric current, after the curve in the graph shows in dc electric current is more than 2.92A, the conduction of MOSFET loss is bigger.

 

 

 

Nevertheless, graph 4 medium dc conduct loss not to apply to much application quite. In the meantime, graph 5 in showed conduct loss to be in mode of CCM (permanent current) , circuit of step up PFC, the knot of 125 ℃ is lukewarm and the trade-off curve below the Vac of communication input voltage of 85V and the working mode that 400 Vdc dc outputs voltage. In the graph, the curvilinear photograph node of MOSFET-IGBT is 2.65A RMS. To PFC circuit character, when communication inputs electric current to be more than 2.65A RMS, MOSFET has bigger conduction loss. Electric current of input of 2.65A PFC communication is equal to MOSFET in by formula the 2.29A RMS of 2 computation earning. MOSFET conducts loss, I2R, use formula the RDS(on) of the electric current of 2 definitions and MOSFET 125 ℃ can be calculated reach. Consider the factor that RDS(on) follows leakage pole electric current to change inside, should conduct loss to still can be changed accurately further, if the graph is shown 6 times,this kind concerns.

 

 

One the name is “ how to be opposite the RDS(on) of power MOSFET the conduction that the dependence that transient state of leakage pole electric current is worth includes inverter of PWM of high frequency three-phase the article described the IEEE of the ” in loss calculation how to determine the impact of leakage pole electric current to conducting loss. Serve as the function of ID, the impact that RDS(on) change attacks to most SMPS develop is very little. For example, in PFC circuit, it is 11A—— when the ID of peak value electric current of FCP11N60 MOSFET the double test condition at the RDS(on) in book of 5.5A (norms) when, the virtual value of RDS(on) and conduct loss to be able to increase 5 ％ .

 

The develop of tall pulse electric current that conducts minimum to occupy sky comparing in MOSFET attacks in the structure, should consider the character that the graph shows 6 times. If FCP11N60 MOSFET job is in a circuit, its leak extremely electric current compares the 20A pulse of 7.5% for nothing to occupy (namely 5.5A RMS) , effective RDS(on) will compare 5.5A (the test electric current in norms book) the 0.32 ohm when are big 25% .

 

 

The RMS electric current in circuit of formulary 2 CCM PFC

 

Type 2 in, iacrms is electric current of input of PFC circuit RMS; Vac is voltage of input of PFC circuit RMS; Vout is dc output voltage.

 

In applying actually, the computational IGBT conduction in similar PFC circuit loss will be more complex, undertake on the IC that because every switch cycle is in,differs. The VCE(sat) of IGBT cannot express by an impedance, simpler and direct method is express its to for impedance RFCE series connection one secures VFCE voltage, VCE(ICE)=ICE×RFCE+VFCE. Then, conduct loss to be able to be calculated the product that is average collector electric current and VFCE, add the square of RMS collector electric current, multiply again with impedance RFCE.

 

Graph the conduction that 5 medium give typical examples considered CCM PFC circuit only loss, assume design target is maintaining what the poorest condition falls to conduct loss to be less than 15W namely. It is with FCP11N60 MOSFET exemple, this circuit is in by limitation 5.8A, and FGP20N6S2 IGBT can be in the communication input of 9.8A works below electric current. It can conduct the power that exceeds MOSFET 70% .

 

Although the conduction of IGBT loss is lesser, but most 600V IGBT is PT (Punch Through, penetrable) model parts of an apparatus. PT parts of an apparatus has NTC (to lose temperature coefficient) characteristic, cannot shunt-wound billabong. Probably, these parts of an apparatus can shoot threshold value voltage through matching bar of VCE(sat) of parts of an apparatus, VGE(TH) () reach machinery to enclose have parallel connection with finite effect, in order to make IGBT chip people the change that temperature can carry consistent. Contrarily, MOSFET has PTC (temperature coefficient) , can offer good voltaic billabong.

 

Close loss — problem to have not end

 

In hard switch, clamp in perceptual circuit, of MOSFET close loss ratio IGBT low much, the reason depends on the electric current pulling end of IGBT, this and cleared graph 1 in the minority of PNP BJT carries stream child about. Graph the 7 function Eoff that showed lukewarm Tj of ICE of collector electric current and knot, its curve has in table of most IGBT data offer. These curves are based on clamp perceptual circuit and test voltage is identical, include loss of energy of electricity pulling end.

 

 

Graph 2 showed the model that is used at measuring IGBT Eoff tests circuit, its test voltage, pursue namely 2 medium VDD, because of the BVCES of different manufacturer and individual parts of an apparatus different. In Lv of the take an examination when comparing parts of an apparatus this checks the VDD in the condition, because be in inferior VDD clamp undertake specific power consumption is reduced check and working will bringing about Eoff below voltage.

 

Reduce grid drive to close impedance to be affected to reducing IGBT Eoff loss infinitesimal. If the graph is shown 1 times, when equivalent majority carries stream child when MOSFET closes, carry in IGBT minority stream child Td(off)I of memory time defer still exists in BJT. Nevertheless, reduce Eoff drive impedance to will reduce rice to strap capacitance (Miller Capacitance) CRES and the electric current that involve the Dv/dt of VCE to cause note the risk in grid drive loop, avoid to make parts of an apparatus slants afresh buy is conduct condition, cause the switch movement of many generation Eoff thereby.

 

ZVS and ZCS develop attack to close loss respect to have an advantage very much in what reduce MOSFET and IGBT. Nevertheless the working advantage of ZVS is done not have in IGBT so big, when because become,the electromotive force that collector voltage rises to allow redundant memory charge to undertake dissipation is worth, can cause Eoff of impulse current pulling end. It is OK that ZCS develop attacks the IGBT Eoff performance with the greatest promotion. Right grid drive order can make IGBT grid signal passes to was not kept clear of before at 0 o’clock in electric current of the 2nd collector, reduce IGBT ZCS Eoff significantly thereby.

 

The Eoff specific power consumption of MOSFET is its Miller drive of speed of drive of capacitance Crss, grid, grid involves source impedance and cause extremely the function of inductance of the parasitism in power circuit method. Lx (of inductance of this circuit parasitism is shown 8 times like the graph) produce an electromotive force, involve loss through restricting electric current to rate falls and increase. When closing, electric current drops speed Di/dt is decided by Lx and VGS(th) . If Lx=5nH, VGS(th)=4V, the biggest electric current drops speed is VGS (Th) / Lx=800A/μs.

 

 

Summary:

 

When choosing power switch parts of an apparatus, do not have the solution of perfect, circuit develop attacks, temperature of working frequency, environment and physical dimension, all these ties can be in there is effect when making optimal choice.

 

In the ZVS that has loss of the smallest Eon and ZCS application, because MOSFET has quicker switch speed and less involve loss, because this can be below more high frequency rate,work.

 

To hard switch application character, the refreshment of MOSFET parasitism diode is characteristic and likely it is a defect. Contrary, because IGBT combination encloses the diode inside and specific application to match, admirable soft restore diode but with more high-speed SMPS parts of an apparatus closes suitably.

 

Hind language: MOSFE and IGBT are distinguished without essence, the “ that people often asks is MOSFET still be IGBT good ” very this problem itself is a mistake. Why to use MOSFET sometimes as to us, sometimes need not MOSFET and use IGBT, cannot have used simply mix bad will distinguish, will decide, need considers this issue with adj method.