design of mosfet

7/31/2019 design of mosfet

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RATING OF FUSE F1

It is calculated as:

Ip (max) = 3.13 xPout

Vdc

Pout = 640 W, Vdc= 2302 = 325V

Ip (max) = 3.13 x

= 6.16A

=> Fuse rating = 6.16/2=4.35 A

640

325


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FILTER CIRCUIT


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FILTER CIRCUIT

EMI suppression capacitors.

The capacitors C1, C2, C3 and C4

are selected as per commonlyused EMC standards.


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FILTER CIRCUIT

ELECTROMAGNETIC COMPATIBILITY (EMC)is the branch that studies the unintentionalgeneration, propagation and reception of

electromagnetic energy with reference to theunwanted effects (Electromagnetic interference)that such energy may induce.


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EMI RATING/CLASSIFICATION For residential, commercial and light industrial

environment we consider CLASS B EMI rating. Standard values of capacitors used as per class B rating

are:

Across line and neutral : 220 nF.

Across line and ground : 10 nF.

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TYPES OF CAPACITORS AS PER SAFETY STANDARDS

As per INTERNATIONAL STANDARD IEC 60384 14

capacitors are classified based on impulse testing as: X1; impulse tested for 4KV.

Y1; impulse tested for 8KV.

X2; impulse tested for 2.5KV.

Y2; impulse tested for 5KV. Similarly X3, Y3 for further lower voltages, which are not

upto safety standards.

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FILTER CIRCUIT

Thus we have used following capacitors inthe ckt as per suitability.

C1 & C2; Type X2 Capacitance = 220 nF.

C3 & C4; Type Y2 Capacitance = 10 nF


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RECTIFIER DESIGN


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RECTIFIER DESIGN

Bridge rectifier circuit changes ACvoltage into DC voltage.

It consists of diodes D1, D2, D3 andD4 as shown.


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INPUT CAPACITOR C5


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INPUT CAPACITOR C5

Cin=

Where is the attempted efficiency of the circuit,taken as 90%.

2 is used for the waveform being sinusoidal.

Po

x fac [(2Vdc(min) )2 - ( Vdc(min))

2 ]


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INPUT CAPACITOR C5

Cin=

Cin= 134.64 x 10-6 F

= 134.64 F.

C5 = 220 F. ( since only 110 F, 220 F avl)

640

0.9 x 50 [(2 x 325)2 - ( 325)2]


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MOSFET DESIGN

As calculated earlier, Ip = 6.16A.

So current across the MOSFET should be in excess of

6.16A.Also breakdown voltage > 325V, since our dc bus is at

325 V.

After 325 V we assume that the is a faulty overvoltage

at the input.


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Range of voltage as per design is 230V to 270V.

ie the voltage can exceed till a maximum value of

2702 = 381V. MOSFETs available are:

MOSFET having VDSS = 350V

MOSFET having VDSS = 500V

Since MOSFET shouldnt breakdown under 381VSo we have selected IRFP 460 having VDSS = 500V

MOSFET DESIGN


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IRFP 460 has drain current Id =20A, which is more than 6.16A.

Also RDS ON= 0.27 RDS ON is the channel resistance between drain and source in

ON state. It is also called the dynamic resistance. Power dissipation on ground.

I2 R = (6.16)2 x 0.27= 10.24W

For leakage inductance spikes which are sinusoidal in nature, whichcause a lot of unaccounted power loss, a multiplication factor of 2

is used. Thus power dissipation per MOSFET = 10.24 x 2 = 14.48W Since two MOSFETs are used, total power dissipated = 28.96W.

Heat sink is selected keeping in mind the above value.

MOSFET DESIGN


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TRANSFORMER SELECTION The mechanical size of a transformer depends on thepower to be transferred and on the operatingfrequency.

Higher the frequency , smaller is the mechanical size. Transformer is designed as.

Core selection.

No of primary turns Np .

No of secondary turns Ns .


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CORE OF TRANSFORMER Material of the core is ferrite.

The transformer core is selected from the TDK EI databook.

Standard transformer selected ETD 39/20/13 as per therequired parameters:

Frequency of operation for SMPS= 100KHz.

Pout

= 640 W.

.


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NUMBER OF PRIMARY TURNS This number determines the magnetic flux density

within the core.

Minimum number of primary turns are calculated as.

Where :

Ae : effective cross-section area of the core, this is wherethe flux density is maximum.

B : is change of flux density.

N1 min


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(EFFECTIVE AREA OFCORE)


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RATE OFCHANGE OF

FLUX DENSITY


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Calculation of maximum on time ie Ton (max)

We have f= 100KHz.

=> T= 1/f = 1/100 x 103 = 10s. Now max value of Ton can be 50%.

But at 50% operation core saturates, thus txr canbecome a short circuit, leading to a failure.

So to avoid saturation a dead time of 10% is providedsuch that: Ton Max = (50 10)% = 40% of T. So we get Ton Max = 4 s.


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N1 min 38 turns.

Secondary turns N2 can be calculated as:

N2= = 80 turns


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SELECTION OF DIODES D9 AND D10 Both the diodes D9 and D10 are ultra fast diodes having

trr = 70ns.

=> fmax

= 1/70 x 10 -3 =0.014 x 109 = 14 MHz.

Such diodes are selected to cater forovershoot/undershoot in freq, since time pd forringing freq is of the order of 125ns

=> fringing = 8MHz. Thus ultra fast diodes cater for overshoot/undershoot

in freq.


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SELECTION OF CAPACITORS C8, C9, C10 Ripple of not more than 5% is accepted.

Vr = => 10=

=> C = = 1.6 x 10-6 = 1.6F.

Idc

2 f C

10.2

2 x 100 x 103 x C

3.22 x 100 x 103 x 10

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design of mosfet