We know the MOSFET in switch power source, IGBT is most core also is the parts of an apparatus that burns out the most easily. Permanent worker of switch parts of an apparatus is made at condition of tall voltage big electric current, bearing very big power comsumption, one but be pressed too or flow to be able to bring about power comsumption to soar too, brilliant circle knot is lukewarm rise quickly, if come loose heat is not seasonable, can cause damage of parts of an apparatus, may accompany explosion even, breakneck.

 

Be familiar with and use SOA correctly, the stability that land of OK and great limit increases switch parts of an apparatus and prolong service life.

 

What is SOA?

 

SOA (Safe Operating Area) it is to point to secure job area, by an a series of leakage that restrict conditional composition VDS of source pole voltage is mixed the graph of 2 dimension coordinate of ID of leakage pole electric current, the voltage when switch parts of an apparatus works normally and electric current should not exceed this limit range.

 

Sketch map of curve of graph 1 SOA

 

To power semiconductor device, can the safe, electricity that has the job reliably and voltage limits, call secure job area, the parts of an apparatus when the electric current that exceeds this range and voltage work can produce damage, cause unit of electric power electron easily ruinous problem. Any power semiconductor device need to give out secure job area, measure the performance of parts of an apparatus on one hand, provide a basis to use parts of an apparatus and design circuit parameter correctly at the same time.

 

The data of switch parts of an apparatus can find the form of SOA almost in manual.

 

The place wants related SOA

 

The limit range of SOA normally by the biggest leakage extremely voltaic ID(max) or the biggest leakage extremely the VD(MAX) of voltage of source of the IDM of pulse electric current, biggest leakage, biggest allow dissipation power PDM of power of dissipation of PD(MAX) or the biggest pulse, guide electrify block RDS(on) decides jointly.

 

The curve of SOA of secure job area of power MOSFET, have 4 attrib border composition normally, explain as follows respectively:

 

1, the attrib border diagonal of wrong upper part of curve of SOA of secure job area, suffer power MOSFET guide electrify block RDS(ON) is restricted.

 

Graph 2 SOA accepts the restriction of RDS(ON)

 

Because be below fixed VGS voltage and ambient conditions, the RDS(ON) of power MOSFET is fixed, because the slope of this diagonal is 1/R(DS(ON)) . Criterion VDS and ID correspondence concern as follows type:

 

 

In the data manual of MOSFET, can find the definition that RDS(ON) is worth and range, following plan institute show:

 

Graph the RDS(ON in 3 data manual)

 

2, curve of SOA of secure job area most the perpendicular border of right, it is to suffer the biggest leakage the limitation of BVDSS of source pole voltage, leak namely source puncture voltage.

 

Graph 4 SOA accepts the restriction of BVDSS

 

BVDSS of voltage of leakage source puncture limitted the scope of the biggest voltage of job of parts of an apparatus, in power MOSFET regular job, if leakage pole is mixed the voltage between source pole is excessive heighten, PN knot slants instead produce avalanche puncture, to ensure safety of parts of an apparatus, closing process and its stable state to fall must susceptive leaks extremely and the highest voltage between source pole should under BVDSS of voltage of leakage source puncture.

 

BVDSS of voltage of leakage source puncture is the least value with the nominal place in table of power MOSFET data. Following plan institute show:

 

Graph the BVDSS in 5 data manual

 

3, curve of SOA of secure job area most above horizontal, suffer the biggest pulse IDM of leakage pole electric current (or continuously leakage pole report notes ID) limitation.

 

Graph 6 SOA accepts the restriction of IDM

 

Some SOA curve can tag the curve below DC and pulse mode respectively, those who need an attention is the biggest electric current that IDM is pulse job status, normally the biggest leakage extremely IDM of pulse electric current is successive leakage extremely of voltaic ID 3 to 4 times, because this pulse electric current wants outclass,successive dc flows. IDM and ID are as follows in the definition in data manual:

 

Graph the ID in 7 data manual and IDM

 

4, a group of diagonal of parallel of right upper part of curve of SOA of secure job area, it is the limitation of the power loss below DC and different odd pulse width.

 

Graph 8 SOA accepts the restriction of power loss

 

The data of MOSFET offerred PD value normally in the watch, PD is worth the power of the biggest loss below condition of the dc that it is DC, following plan institute show:

 

Graph the PD in 9 data manual

 

The PDM of power of the biggest loss below different pulse width needs computation to get normally.

 

The computational formula of the PD of power of the biggest loss when DC is:

 

 

Among them Tjmax is the biggest bear lukewarm, TC is housing lukewarm, rθJC is stable state thermal resistance, these 3 values can be checked in data manual.

 

The computational formula of the PDM of pulse dissipation power when different pulse width is:

 

 

Among them Tjmax is the biggest bear lukewarm, TC is housing lukewarm, zθJC is coefficient of thermal resistance of normalization transient state, rθJC is stable state thermal resistance. ZθJC is OK check in the graph of the pulse width in the data manual of MOSFET and ZθJC, because this can come through pulse width,computation gives PDM.

 

Graph 10 pulse width and plan of concern of thermal resistance of normalization transient state

 

SOA note

 

In manual of power MOSFET data, relevant limit parameter and curve of SOA of secure job area are the computational value that is based on ℃ of working temperature TC =25 to fall.

 

For example, the BVDSS that a MOS is in charge of is 600V, but this 600V is the value in 25 ℃ , if the job is in – when 25 ℃ , criterion BVDSS may have 550V only. Following plan institute show:

 

Graph the BVDSS below 11 different temperature

 

In real work, the TC temperature of power MOSFET, it is 25 ℃ impossibly absolutely, normally ℃ of far outclass 25, when because this is mixed in actual set,using SOA, must undertake amend and falling to SOA limit requirement according to actual condition the forehead.

 

For example, below different working temperature, different pulse electric current or pulse width condition, the value of RDS(ON) can differ. Offerred temperature normally in the data manual of power MOSFET – the diagnostic graph of RDS(ON) , following plan institute show:

 

Graph 12 temperature – RDS(ON) concern plan

 

The relation curve from RDS(ON) and temperature is visible, should written guarantee lukewarm lift from 25 ℃ 110 ℃ , guide electrify block raised one times, temperature is higher, the secure job area that RDS(ON) place qualifies is contractible, need what fall with specific work environment to guide safety of electrify block demarcate works in applying actually so area.

 

Same, the ambient conditions that ID(max) , VD(MAX) and PD(MAX) need a basis to work actually undertakes the forehead is mixed falling amend.

 

SOA actual measurement

 

The SOA test application of oscillograph is very simple, probe of use voltage, electric current checks the VDS that switch is in charge of and IDM normally, open SOA to analyse a function, contrast the SOA parameter that the SOA data of data manual sets good oscillograph can.

 

With FCP22N60N this MOSFET is exemple, we examine data manual, the relevant parameter of successive job mode is as follows:

 

Manual of data of graph 13 FCP22N60N

 

We will set the SOA parameter of oscillograph, BVDSS correspondence is worth ” at “ voltage demarcate, ID correspondence is worth ” at demarcate of “ electric current, PD correspondence is worth ” at “ power demarcate, RDS(ON) correspondence is worth ” at “Rds(on) demarcate, the limits of coordinate of voltage electric current with appropriate at the same time setting (namely maximum of voltage electric current and the least value) , following plan institute show parameter setting interface:

 

Graph 14 parameter install an interface

 

The SOA pattern plate that oscillograph makes, can undertake contrast with the SOA of the corresponding condition in MOSFET data manual, following plan institute are shown. In be being used actually of course, still need a basis current environment and working requirement undertake to condition of SOA demarcate area the forehead is mixed falling amend.

 

The SOA in pattern plate of graph 15 SOA and data manual is comparative

 

The newest SOA function of ZDS4000 oscillograph still provided following test functions:

 

N of ● innovation sex holds the parameter of pulse width Tp to install, the meeting when the test decides whether does pulse width reach Tp time value;

● support guides the parameter of electrify block Rdson is installed, affect the area of internal resistance demarcate of SOA pattern plate;

● backs successive test, and the gross that statistic fails through reaching second, this mode can be used at baking machine test continuously;

● supports lay a finger on (weaveform exceeds region of place of safety) stop, operation of clew of automatic cut scheme, sound;

Area of ● safety work can pass voltage, electric current, power to restrict set, also can pass much coordinate dot to define set oneself;

Area of ● safety work supports logarithm coordinate and linear coordinate to show.

 

Graph actual measurement of 16 oscillograph SOA

 

The article is reprinted from science and technology of ZLG make contributions.