This type of power MOSFET is widely used in digital computers. The construction of enhancement type power MOSFET is shown in figure above .This is an n-channel device.However as seen in the figure,the p-substrate extends right up to the silicon dioxide layer.Thus there is no n-channel between drain and source. The above figure shows the connections.When the gate voltage is zero,drain battery tries to push free electrons from the source to the drain.However the p-substrate has only a few thermally produced free electrons and some electrons due to surface leakage.Therefore the drain current is almost zero.When gate is positive(VGS>0)the gate attracts free electrons into the p-substrate region these free electrons recombine with holes near silicon dioxide layer.When VGS is large read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

Drain characteristics of an n-channel MOSFET is shown in figure below. VGS can be positive and negative.The characteristics for p-channel are similar to the above figure excepts signs of current and voltage are reversed. The transconductance curve(transfer characteristics)of depletion type MOSFET is shown in figure below. This characteristcs shows the variation of ID with VGS.IDSS denoteS the drain current with shorted gate.The curve extends on both sides ie VGS can be negative as well as positive.Since VGS can be positive also IDSS is not maximum value of drain current. This device has three regions.The ohmic region,active region and breakdown region.The rising position of the drain characteristics is the ohmic region.The device acts as resistor.The drain current is nearly constant read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

i) Negative Gate Operation In the figure given below a negative bias is applied to the gate The negative voltage depletes the conducting channel of majority carriers electrons and controls their flow. The gate and channel forms a parallel plate capacitor with silicon dioxide layer as dielectric.The negative gate bias causes concentration of electrons on the gate.These electrons repel the conduction band electrons in the n-channel leaving a positive ions layer as shown.More negative gate voltage,the greater is the depletion of electrons in n-channel. ii) Positive Gate Operation A depletion mode MOSFET when gate bias is positive is shown in figure below. The gate and channel can again be thought of as a capacitor positive charge on gate induce negative charge in n-channel.These negative read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

Power MOSFET is a voltage controlled device and it requires only small input current.It has extremely high input impedance and is widely used in switching devices.The switching is high and the switching time is in the order of nanoseconds.They are used in low power high frequency converters.MOSFETs are of two types. i) Depletion Type MOSFET ii) Enhancement type MOSFET i) Depletion Type MOSFET A depletion type n-channel MOSFET has a lightly doped p-type substrate into which two highly doped n-region(n+) are diffused.These two regions acts as drain and source.A thin insulating silicon dioxide layer is grown across the semiconductor surface. The two holes cut into the oxide layer allow contact with the source and drain.A metal layer is then deposited on the oxide.This layer forms the read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

A generating station in which nuclear energy is converted into electrical energy is known as a nuclear power station In nuclear power station, heavy elements such as Uranium (U235) or Thorium (Th232) are subjected to nuclear fission in a special apparatus known as a reactor. The heat energy thus released is utilised in raising steam at high temperature and pressure. The steam runs the steam turbine which converts steam energy into mechanical energy. The turbine drives the alternator which converts mechanical energy into electrical energy. The most important feature of a nuclear power station is that huge amount of electrical energy can be produced from a relatively small amount of nuclear fuel as compared to other conventional types of power stations. It has been found that complete read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

Power transistors are finding increasing popularity in low to medium power applications.A power transistor has low current gain and requires continuous base drive during on-state conditions but doesn’t require forced commutations.Circuitry power transistors can be used in high switching frequency,permitting size reduction of electromagnetic components and can provide current limit protection by base drive circuit.Power transistor cannot withstand reverse voltage and application is limited to dc voltage for inverters and choppers. A transistor is a three layer pnp or npn semiconductor device having two junctions.This type of transistors is know as bipolar junction transistor(BJT).The structure and symbol of npn transistor is shown below. The three terminals of the device are read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

A power diode is a two terminal p-n junction device and a p-n junction normally formed by allowing diffusion and epitaxial growth structure of a power diode and symbol are shown in figure below. High power diodes are silicon-rectifiers that can operate at high junction temperatures.Power diodes have larger Power,Voltage and Current handling capabilities than ordinary signal diodes.In addition,the switching frequencies of power diodes are low as compared to signal diodes. The voltage current characteristics of power diodes is shown in figure below When the anode potential is positive with respect to cathode,the diode is said to be forward biased,the diode conducts and behaves essentially as a closed switch.A conducting diode has a relatively small forward voltage drop across it and the read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

The electronics power conversion circuit that convert and control electrical power, use Power Semiconductor devices.  These devices operate in the switching mode, which causes the losses to be reduced and therefore the conversion efficiency is to be improved.  However the disadvantages of switching mode operation are the generation of harmonics and the fact that the converter system tends to be more complex. Power Semiconductor Devices are classified i. Power Diode ii. Power bipolar junction transistor iii. Power MOSFET iv. Insulated gate bipolar Junction transistor v. Thyristors Share and Enjoy: read more

If you enjoyed this post, make sure you subscribe to my RSS feed!