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Two power MOSFETs in the
package . Each of these components can sustain a blocking voltage of 120  and a continuous current of 30 .
A power MOSFET is a specific type of metal oxide semiconductor field-effect transistor () designed to handle significant power levels.
Compared to the other , for example insulated-gate bipolar transistor (), , its main advantages are high
speed and good efficiency at low voltages. It shares with the IGBT an isolated gate that makes it easy to drive. They can be subject to low gain, sometimes to degree that the gate voltage needs to be higher than the voltage under control.
The design of power MOSFETs was made possible by the evolution of
technology, developed for manufacturing
in the late 1970s. The power MOSFET shares its operating principle with its low-power counterpart, the lateral MOSFET.
The power MOSFET is the most widely used low-voltage (that is, less than 200 V) switch. It can be found in most , , and low voltage .
Fig. 1: Cross section of a VDMOS, showing an elementary cell. Note that a cell is very small (some micrometres to some tens of micrometres wide), and that a power MOSFET is composed of several thousand of them.
Several structures had been explored at the beginning of the 1980s, when the first power MOSFETs were introduced. However, most of them have been abandoned (at least until recently) in favour of the Vertical Diffused MOS (VDMOS) structure (also called Double-Diffused MOS or simply DMOS).
The cross section of a VDMOS (see figure 1) shows the "verticality" of the device: it can be seen that the source electrode is placed over the drain, resulting in a current mainly vertical when the transistor is in the on-state. The "" in VDMOS refers to the manufacturing process: the P wells (see figure 1) are obtained by a diffusion process (actually a double diffusion process to get the P and N+ regions, hence the name double diffused).
Power MOSFETs have a different structure from the lateral MOSFET: as with most power devices, their structure is vertical and not planar. In a planar structure, the current and
ratings are both functions of the channel dimensions (respectively width and length of the channel), resulting in inefficient use of the "silicon estate". With a vertical structure, the voltage rating of the transistor is a function of the
and thickness of the N
layer (see cross section), while the current rating is a function of the channel width. This makes possible for the transistor to sustain both high blocking voltage and high current within a compact piece of silicon.
It is worth noting that power MOSFETs with lateral structure exist. They are mainly used in high-end audio amplifiers. Their advantage is a better behaviour in the saturated region (corresponding to the linear region of a ) than the vertical MOSFETs. Vertical MOSFETs are designed for switching applications, so they are only used in On or Off states.
Fig.2: Contribution of the different parts of the MOSFET to the on-state resistance.
When the power MOSFET is in the on-state (see
for a discussion on operation modes), it exhibits a resistive behaviour between the drain and source terminals. It can be seen in figure 2 that this resistance (called RDSon for "drain to source resistance in on-state") is the sum of many elementary contributions:
RS is the source resistance. It represents all resistances between the source terminal of the package to the channel of the MOSFET: resistance of the , of the source metallisation, and of the N+
Rch. This is the channel resistance. It is inversely proportional to the channel width, and for a given die size, to the channel density. The channel resistance is one of the main contributors to the RDSon of low-voltage MOSFETs, and intensive work has been carried out to reduce their cell size in order to increase
Ra is the access resistance. It represents the resistance of the
zone directly under the gate electrode, where the direction of the current changes from horizontal (in the channel) to vertical (to the drain contact);
RJFET is the detrimental effect of the cell size reduction mentioned above: the P implantations (see figure 1) form the gates of a parasitic
transistor that tend to reduce the width
Rn is the resistance of the epitaxial layer. As the role of this layer is to sustain the blocking voltage, Rn is directly related to the voltage rating of the device. A high voltage MOSFET requires a thick, low-doped layer (i.e. highly resistive), whereas a low-voltage transistor only requires a thin layer with a higher doping level (i.e. less resistive). As a result, Rn is the main factor responsible for the resistance of high-voltage MOSFETs;
RD is the equivalent of RS for the drain. It represents the resistance of the transistor substrate (note that the cross section in figure 1 is not at scale, the bottom N+ layer is actually the thickest) and of the package connections.
Fig. 3: The RDSon of the MOSFETs increase with their voltage rating.
When in the OFF-state, the power MOSFET is equivalent to a PIN diode (constituted by the P+ diffusion, the N-
layer and the N+ substrate). When this highly non-symmetrical structure is reverse-biased, the space-charge region extends principally on the light-doped side, i.e. over the N- layer. This means that this layer has to withstand most of the MOSFET's OFF-state drain-to-source voltage.
However, when the MOSFET is in the ON-state, this N- layer has no function. Furthermore, as it is a lightly doped region, its intrinsic resistivity is non-negligible and adds to the MOSFET's ON-state Drain-to-Source Resistance (RDSon) (this is the Rn resistance in figure 2).
Two main parameters govern both the breakdown voltage and the RDSon of the transistor: the doping level and the thickness of the N-
layer. The thicker the layer and the lower its doping level, the higher the breakdown voltage. On the contrary, the thinner the layer and the higher the doping level, the lower the RDSon (and therefore the lower the conduction losses of the MOSFET). Therefore, it can be seen that there is a trade-off in the design of a MOSFET, between its voltage rating and its ON-state resistance. This is demonstrated by the plot in figure 3.
It can be seen in figure 1 that the source metallization connects both the N+ and P implantations, although the operating principle of the MOSFET only requires the source to be connected to the N+ zone. However, if it were, this would result in a floating P zone between the N-doped source and drain, which is equivalent to a
transistor with a non-connected base. Under certain conditions (under high drain current, when the on-state drain to source voltage is in the order of some volts), this parasitic NPN transistor would be triggered, making the MOSFET uncontrollable. The connection of the P implantation to the source metallization shorts the base of the parasitic transistor to its emitter (the source of the MOSFET) and thus prevents spurious latching.
This solution, however, creates a
between the drain (cathode) and the source (anode) of the MOSFET, making it able to block current in only one direction.
Body diodes may be utilized as
for inductive loads in configurations such as
or half bridge. While these diodes usually have rather high forward voltage drop, they can handle large currents and are sufficient in many applications, reducing part count, and thus, device cost and board space.
Fig. 4: Location of the intrinsic capacitances of a power MOSFET.
Because of their unipolar nature, the power MOSFET can switch at very high speed. Indeed, there is no need to remove minority carriers as with bipolar devices.
The only intrinsic limitation in commutation speed is due to the internal capacitances of the MOSFET (see figure 4). These capacitances must be charged or discharged when the transistor switches. This can be a relatively slow process because the current that flows through the gate capacitances is limited by the external driver circuit. This circuit will actually dictate the commutation speed of the transistor (assuming the power circuit has sufficiently low inductance).
In the MOSFET , the capacitances are often named Ciss (input capacitance, drain and source terminal shorted), Coss (output capacitance, gate and source shorted), and Crss (reverse transfer capacitance, gate and source shorted). The relationship between these capacitances and those described below is:
Where CGS, CGD and CDS are respectively the gate-to-source, gate-to-drain and drain-to-source capacitances (see below). Manufacturers prefer to quote Ciss, Coss and Crss because they can be directly measured on the transistor. However, as CGS, CGD and CDS are closer to the physical meaning, they will be used in the remaining of this article.
The CGS capacitance is constituted by the parallel connection of CoxN+, CoxP and Coxm (see figure 4). As the N+ and P regions are highly doped, the two former capacitances can be considered as constant. Coxm is the capacitance between the (polysilicon) gate and the (metal) source electrode, so it is also constant. Therefore, it is common practice to consider CGS as a constant capacitance, i.e. its value does not depend on the transistor state.
The CGD capacitance can be seen as the connection in series of two elementary capacitances. The first one is the oxide capacitance (CoxD), constituted by the gate electrode, the silicon dioxide and the top of the N epitaxial layer. It has a constant value. The second capacitance (CGDj) is caused by the extension of the
when the MOSFET is in off-state. Therefore, it is dependent upon the drain to source voltage. From this, the value of CGD is:
The width of the space-charge region is given by
of the Silicon, q is the
charge, and N is the
level. The value of CGDj can be approximated using the expression of the :
Where AGD is the surface area of the gate-drain overlap. Therefore, it comes:
It can be seen that CGDj (and thus CGD) is a capacitance which value is dependent upon the gate to drain voltage. As this voltage increases, the capacitance decreases. When the MOSFET is in on-state, CGDj is shunted, so the gate to drain capacitance remains equal to CoxD, a constant value.
As the source metallization overlaps the P-wells (see figure 1), the drain and source terminals are separated by a . Therefore, CDS is the junction capacitance. This is a non-linear capacitance, and its value can be calculated using the same equation as for CGDj.
Equivalent circuit of a power MOSFET, including the dynamic elements (capacitors, inductors), the parasitic resistors, the body diode.
To operate, the MOSFET must be connected to the external circuit, most of the time using
(although alternative techniques are investigated). These connections exhibit a parasitic inductance, which is in no way specific to the MOSFET technology, but has important effects because of the high commutation speeds. Parasitic inductances tend to maintain their current constant and generate overvoltage during the transistor turn off, resulting in increasing commutation losses.
A parasitic inductance can be associated with each terminal of the MOSFET. They have different effects:
the gate inductance has little influence (assuming it is lower than some hundreds of nanohenries), because the current gradients on the gate are relatively slow. In some cases, however, the gate inductance and the input capacitance of the transistor can constitute an . This must be avoided as it results in very high commutation losses (up to the destruction of the device). On a typical design, parasitic inductances are kept low enough to pre
the drain inductance tends to reduce the drain voltage when the MOSFET turns on, so it reduces turn on losses. However, as it creates an overvoltage during turn-off, it increases turn-
the source parasitic inductance has the same behaviour as the drain inductance, plus a
effect that makes commutation last longer, thus increasing commutation losses.
at the beginning of a fast turn-on, due to the source inductance, the voltage at the source (on the die) will be able to jump up as well the internal VGS voltage will remain low for a longer time, therefore delaying turn-on.
at the beginning of a fast turn-off, as current through the source inductance decreases sharply, the resulting voltage across it goes negative (with respect to the lead outside the package) raising the internal VGS voltage, keeping the MOSFET on, and therefore delaying turn-off.
The gate oxide is very thin (100 nm or less), so it can only sustain a limited voltage. In the datasheets, manufacturers often state a maximum gate to source voltage, around 20 V, and exceeding this limit can result in destruction of the component. Furthermore, a high gate to source voltage reduces significantly the lifetime of the MOSFET, with little to no advantage on RDSon reduction.
To deal with this issue, a
circuit is often used.
Power MOSFETs have a maximum specified drain to source voltage (when turned off), beyond which
may occur. Exceeding the breakdown voltage causes the device to conduct, potentially damaging it and other circuit elements due to excessive power dissipation.
The drain current must generally stay below a certain specified value (maximum continuous drain current). It can reach higher values for very short durations of time (maximum pulsed drain current, sometimes specified for various pulse durations). The drain current is limited by heating due to
in internal components such as , and other phenomena such as
in the metal layer.
(TJ) of the MOSFET must stay under a specified maximum value for the device to function reliably, determined by MOSFET die layout and packaging materials. The packaging often limits the maximum junction temperature, due to the molding compound and (where used) epoxy characteristics.
The maximum operating ambient temperature is determined by the power dissipation and . The junction-to-case thermal resistance is intrinsic to th the case-to-ambient thermal resistance is largely dependent on the board/mounting layout, heatsinking area and air/fluid flow.
The type of power dissipation, whether continuous or pulsed, affects the maximum , due in general, the lower the frequency of pulses for a given power dissipation, the higher maximum operating ambient temperature, due to allowing a longer interval for the device to cool down. Models, such as a , can be used to analyze temperature dynamics from power transients.
defines the combined ranges of drain current and drain to source voltage the power MOSFET is able to handle without damage. It is represented graphically as an area in the plane defined by these two parameters. Both drain current and drain-to-source voltage must stay below their respective maximum values, but their product must also stay below the maximum power dissipation the device is able to handle. Thus, the device cannot be operated at its maximum current and maximum voltage simultaneously.
The equivalent circuit for a MOSFET consists of one MOSFET in parallel with a parasitic BJT (). If the BJT turns ON, it cannot be turned off since the gate has no control over it. This phenomenon is known as ??, which can lead to device destruction. The BJT can be turned on due to a voltage drop across the p-type body region. To avoid latchup, the body and the source are typically short circuited within the device package.
This power MOSFET has a meshed gate, with square cells
The gate layout of this MOSFET is constituted of parallel stripes.
As described above, the current handling capability of a power MOSFET is determined by its gate channel width. The gate channel width is the third (Z-axis) dimension of the cross-sections pictured.
To minimize cost and size, it is valuable to keep the transistor's die area size as small as possible. Therefore, optimizations have been developed to increase the width of the channel surface area (i.e. increase the "channel density"). They mainly consist of creating cellular structures repeated over the whole area of the MOSFET die. Several shapes have been proposed for these cells, the most famous being the 's "Hexfet" (hexagonal shape).
Another way to increase the channel density is to reduce the size of the elementary structure. This allows for more cells in a given surface area, and therefore more channel width. However, as the cell size shrinks, it becomes more difficult to ensure proper contact of every cell. To overcome this, a "strip" structure is often used (see figure). It is less efficient than a cellular structure of equivalent resolution in terms of channel density, but can cope with smaller pitch.
The VMOS structure has a V-groove at the gate region
The UMOS has a trench gate. It is intended to increase the channel density by making the channel vertical
A P-substrate MOSFET (often referred to as PMOS) is a MOSFET with opposite doping types (N instead of P and P instead of N in the cross-section in figure 1). This MOSFET is made using a P-type substrate, with a P- epitaxy. As the channel sits in a N-region, this transistor is turned on by a negative gate to source voltage. This makes it desirable in a , where one of the terminals of the switch is connected to the high side of the input voltage: with a N-MOSFET, this configuration requires to apply to the gate a voltage equal to , whereas no voltage over
is required with a P-MOSFET.
The main disadvantage of this type of MOSFET is the poor on-state performance: it uses holes as , which have a much lower
is directly related to mobility, a given PMOS will have a
three times higher than a N-MOSFET with the same dimensions.
structure has a V-groove at the gate region and was used for the first commercial devices.
In this power MOSFET structure, also called trench-MOS, the gate electrode is buried in a trench etched in the silicon. This results in a vertical channel. The main interest of the structure is the absence of the JFET effect. The name of the structure comes from the U-shape of the trench.
Especially for voltages beyond 500 V some manufacturers, including
with its CoolMOS products, have begun to use a charge compensation principle. With this technology, the resistance in the
layer as biggest contributor in high voltage MOSFETs can be reduced by a factor of greater than 5.
Seeking to improve the manufacturing efficiency and reliability of super-junction MOSFETs,
Electronics developed a super-junction structure with a deep-trench process technique. This technology entails etching trenches in the low-impurity N-type material to form P-type regions. This process overcomes problems inherent to the multi-level epitaxial growth approach and results in extremely low on-resistance and reduced internal capacitance.
S. M. Sze Modern semiconductor device physics John Wiley and Sons, Inc 1998
Pierre Alo?si, Les transistors MOS de puissance in Interrupteurs électroniques de puissance, traite EGEM, under the direction of Robert Perret, Lavoisier, Paris, 2003 [in French]
Duncan A. Grant, John Gowar POWER MOSFETS: Theory and Applications John Wiley and Sons, Inc
"Power Semiconductor Devices", B. Jayant Baliga, PWS publishing Company, Boston.
: Hidden categories:一般的MOS功率管能承受多少A电流？现在一块充电板想让它输出达10A电流，用2个功率管不知道能否承受得住_百度知道
一般的MOS功率管能承受多少A电流？现在一块充电板想让它输出达10A电流，用2个功率管不知道能否承受得住
我有更好的答案
按默认排序
大电流的场效应管许多许多，10A不算大。目前市场上容易买到的12N60可达12A/600V再有IRF640可达18A200V,不知道你需要的电压是多少？
你的耐压要多高的？如果600v的那就用 12n60可以了，这颗mos是12a的电流600v耐压。看你留的余量多少咯。
作为开关电源的功率管吗？用电磁炉功率管即可
先从变压器下手
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功率管的相关知识
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出门在外也不愁UPS常用的电力电子器件有？A：GTR.B:MOSFET.C:IGBT.D:GTO_百度知道
UPS常用的电力电子器件有？A：GTR.B:MOSFET.C:IGBT.D:GTO
到底选哪个啊？是多选题
.B:MOSFETC:IGBT.
其他类似问题
电力电子器件的相关知识
其他3条回答
UPS的中文意思为“不间断电源”，是英语“Uninterruptible Power Supply”的缩写，它可以保障计算机系统在停电之后继续工作一段时间以使用户能够紧急存盘，使您不致因停电而影响工作或丢失数据。它在计算机系统和网络应用中，主要起到两个作用：一是应急使用，防止突然断电而影响正常工作，给计算机造成损害；二是消除市电上的电涌、瞬间高电压、瞬间低电压、电线噪声和频率偏移等“电源污染”，改善电源质量，为计算机系统提供高质量的电源。 从基本应用原理上讲，UPS是一种含有储能装置，以逆变器为主要元件，稳压稳频输出的电源保护设备。主要由整流器、蓄电池、逆变器和静态开关等几部分组成。 1)整流器：整流器是一个整流装置，简单的说就是将交流（AC）转化为直流（DC）的装置。它有两个主要功能：第一，将交流电（AC）变成直流电(DC)，经滤波后供给负载，或者供给逆变器；第二，给蓄电池提供充电电压。因此，它同时又起到一个充电器的作用； 2)蓄电池：蓄电池是UPS用来作为储存电能的装置，它由若干个电池串联而成，其容量大小决定了其维持放电（供电）的时间。其主要功能是：1当市电正常时，将电能转换成化学能储存在电池内部。2当市电故障时，将化学能转换成电能提供给逆变器或负载； 3)逆变器：通俗的讲，逆变器是一种将直流电（DC）转化为交流电（AC）的装置。它由逆变桥、控制逻辑和滤波电路组成； 4)静态开关：静态开关又称静止开关，它是一种无触点开关，是用两个可控硅（SCR）反向并联组成的一种交流开关，其闭合和断开由逻辑控制器控制。分为转换型和并机型两种。转换型开关主要用于两路电源供电的系统，其作用是实现从一路到另一路的自动切换；并机型开关主要用于并联逆变器与市电或多台逆变器。 GTO是可关断晶闸管,GTR是大功率晶体管,MOSFET是场效应晶体管,IGBT是GTR与MOSFET是合成器件.所以，这道题考的就是整流、逆变、静态开关所需要的元件，在大功率UPS里，ABCD应该都有用到。
看UPS容量的，一般选用IGBT.
C.新型的UPS都用IGBT了。老式的可能用到GTO。GTR从来都没用过。MOSFET容量太小。只有IGBT才是容量大，而且技术成熟的电子器件。都是相对UPS来讲的。
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出门在外也不愁