Use SiC JFET is close to perfect switch
[introduction] carborundum (SiC) JFET hard usage, have high energy avalanche and short circuit to be able to bear or endure suffer rating, and notable is, they guide in the FOM of area of every unit chip respect of A of × of electrify block R DS(on) beat all and other technology, the academic limit that achieved value to be close to material (graph 1) . This quality factor matters to the real property of switch and its economy directly, compare with competitive technology photograph, the chip amount of every brilliant circle is more, function comparatives.
Carborundum (SiC) JFET hard usage, have high energy avalanche and short circuit to be able to bear or endure suffer rating, and notable is, they guide in the FOM of area of every unit chip respect of A of × of electrify block R DS(on) beat all and other technology, the academic limit that achieved value to be close to material (graph 1) . This quality factor matters to the real property of switch and its economy directly, compare with competitive technology photograph, the chip amount of every brilliant circle is more, function comparatives.
Graph 1: The puncture voltage of the academic limit of A of × of R DS(on) and switch technology
Can be we still done weller?
UnitedSiC (it is Qorvo now) SiC in all source in all bar is had in a lot of application showing an advantage, but can be they still done weller? This parts of an apparatus includes the SiC JFET that cascade arranges and Si-MOSFET, often involve character in order to come true. Look from detail, if the graph is shown 2 times, formed in all source in all bar, among them the source of Si-MOSFET switch SiC JFET extremely, when because this is become,Si-MOSFET is shut, JFET source extremely float is, shut JFET thereby. Guide when MOSFET when connecting, JFET grid and source are extremely significant short circuit, guide its.
Graph 2: Of SiC FET normal in all source in all bar is arranged
In all source in all bar configuration makes through simple grid drive the component is used easily, but reduced can charge a sex. In all source in all bar switch speed basically leaks by JFET grid extremely capacitance and to Si-MOSFET from JFET grid the R G of resistor of in-house series connection of source pole decides. RG _ is the value that defines beforehand and cannot visit. Si-MOSFET grid is finite to the influence of speed, because do not have capacitance of JFET leakage source actually, the grid that can pass its oneself otherwise leakage pole capacitance answers voltaic feedback MOSFET grid, allow to use MOSFET grid resistor to control changeover rate thereby. To hard switch, changing rate control come true through adding an exterior bumper, this is a feasible solution, have additional power comsumption hardly. UnitedSiC is cascade SiC FET ” user guideline ” offerred commendatory bumper and grid resistor to be worth.
Another characteristic that cascade arranges is, when the cascade of series connection forms the spur track of the bridge, restore effect what existence is showing reversely. This is not to come from parasitism body diode, however as a result of follow on current in all the short time that the JFET of bar is shut in the defer when its grid capacitance discharges and brings about in all conducts the source jackknife. The result is to restore charge to have nothing to do with temperature and electric current greatly reversely. Carry on one’s shoulder of this extensive telegram in reply is direct shadow fugleman knows switch loss.
JFET itself in some way can be a better switch, important is: The simple control that changes rate, lower guide electrify block and lower retrorse extensive telegram in reply carry on his shoulder or back.
Grid of segregation SiC JFET in order to obtain bigger flexibility
To the application of inferior switch frequency, better arrangement is JFET grid derivative to exterior join, if pursue,3 are shown. Si-MOSFET can regard as simply now ” enable ” , when can be being used at ensuring to close to start or the condition when control power source is unusually missing.
Graph 3: SiC JFET + Si MOSFET ” double grid ” , unitedSiC (it is Qorvo now) component
When controlling JFET grid directly, without leakage source capacitance, outputting capacitance C OSS is JFET grid actually C GD of leakage pole capacitance, complete by grid driver is not load charges. This means switch speed to be able to be controlled by grid resistor directly, paralell connection gets simplifying. Exterior bumper now is optional, can save space and cost. When be used at bridge-type circuit, effect of carry on one’s shoulder of extensive telegram in reply comes from at the output electric capacity to JFET of follow on current (C GD) charges; Its grid tension is constant. Accordingly, restore effect to be reduced greatly reversely, subsequently and those who come is E ON reduce. Involve rate apparent under the tradition in all source in all bar, this is ideal in electric machinery drive and SSCB/SSR application, but apply to DC/DC converter and other SMPS, e OFF loss may be too big.
The 3rd quadrantal balance
When electric current from the source extremely flow to leakage pole and when grid is shut, the JFET of direct drive differs in the function of the 3rd quadrant. Standard cascade is conducted reversely through Si-MOSFET body diode and bring about JFET passageway to guide, bring about low V SD thereby: Silicon detector is pressed fall add JFET to guide electrify block. To double grid component, if grid guides,be connected or JFET grid – leakage pole voltage exceeds voltage of its threshold value, retrorse electric current will shed JFET. In other words, inside time of bridge circuit dead band, v SD will include ” inflection point voltage ” , this voltage is equal to grid to be added for more negative than threshold value voltage voltage by drive JFET guides electrify block. This may be a few bend over. Power loss of this kind of dead band opens the central Shaanxi plain in the 10 electric machinery drive to 20 KHz negligible, have nothing to do completely with SSCB/SSR application. To more high-frequency SMPS application, need is added turn over shunt-wound SiC diode. It is OK to turn over shunt-wound diode very small, because it is in only,bear the weight of inside area time to death peak value electric current.
Still have more results
So far, we can control switch rate directly and decrease to reinstate charge reversely greatly, but the advantage that still has another easy implementation. In the standard in all source in all in bar, JFET passes its grid by Si-MOSFET source pole short circuit and guide. Use double grid part, can will guide electrify presses a setting to be a bit, enhance JFET passageway further, make R DS(on) is reduced thereby make an appointment with 15% , faster guide, and do not have an influence to closing. Below all job temperature, JFET grid – source pole PN writtens guarantee ” inflection point ” lower part has a 2 V driving voltage, because this has very small grid only,electric current can flow. This electric current is a few milliampere about, because this minority carries,flow child infuse is negligible not plan. This is implementation conducts loss to showing the simple method that reduce.
grid drive still has another profit: JFET grid – source pole diode is pressed fall can use as real time piece on the temperature that temperature measures is sensitive parameter. For example, – the temperature coefficient of linear V GS that C of 3.22 MV/ ° is UnitedSiC Gen 3 1200 V JFET. Accordingly, the grid that can fall through measuring on-state – source pole voltage and grid electric current will detect directly chip temperature.
The method of a kind of simpler affirmatory temperature tubal core is the grid leakage current that measures Si-MOSFET. But ask an attention, as a result of the difference between the component, this needs calibration. Like JFET V GS, MOSFET grid leak (very small) as direct as temperature relevant. Through be in Si-MOSFET chip pile the coping of JFET chip, it is OK and accurate the temperature that measures MOSFET and JFET. Si-MOSFET maintains on-state normally, because this uses poor component,amplifier measures its grid resistance the static voltage of two end is to feel a kind of when measure temperature simple method.
Actual circuit showed this skill
The grid of drive JFET may look not familiar, close condition to need to lose voltage, 0 bend over of on-state need ≥ , but it and drive silicon or SiC MOSFET are very actually similar, they are pressed for negaive electricity by drive normally (graph 4) .
Graph 4: Join with standard driver and bumper directly cascade JFET door
In this circuit, add component is bumper Q1, it standard driver the on-state of U1 is outputted from for example + changeover of 15 V n offers to pass manostat + 2 V. The inferior MOSFET in Q1 is optional — shows driver IC has the off-state output that can use directly, but the MOSFET in U1 offers addition voltaic size, this may be very useful to shunt-wound equipment. The Si-MOSFET of double grid part keeps apart driver control by another. Shedding link electrify continuously but below the circumstance that driver cuts off the power, neat accept diode D2 and D3 ensure JFET restores to cascade is operated and maintain close position. Traditional DESAT detects include normally in driver, the R4 that this can pursue medium through the principle and D1 use JFET to come true.
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