Compare JFET’s and MOSFET’s.

Comparison of JFET’s and MOSFET’s:

JFETs and MOSFETs are quite similar in their operating principles and in their electrical characteristics. However, they differ in some aspects, as detailed below :

JFETs vs MOSFETs
How it operates	JFETs	MOSFETs
	Voltage controlled	Voltage controlled.
Gain (Transconductance)	Low transconductance (gain)	Low transconductance (gain)
Input Impedance	JFETs are depletion type transistors only.	MOSFETs can be depletion type or enhancement type.
Input Impedance	JFETs offer less input impedance than MOSFETs. JFETs typically offer about 109 Ω of impedance.	MOSFETs offer greater input impedance. MOSFETs typically offer about 1014Ω of impedance, sometimes greater.
Cost	JFETs are somewhat cheaper to manufacture than MOSFETs. They have a less sophisticated manufacturing process.	MOSFETs are slightly more expensive to manufacture than JFETs.
Susceptibility to Damage	JFETs are less susceptible to damage from ESD because they have greater input capacitance than MOSFETs.	MOSFETs are more susceptible to damage from ESD because the metal oxide insulator that insulates the gate from the drain-source channel lowers the capacitance of the gate. This makes high voltage more able to break through and destroy the transistor.
Popularity	JFETs are less popular than MOSFETs.	MOSFETs are more popular and widely used today than JFETs.

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Write down some common applications of Diodes.

Some common applications of Diodes: 

1. Power supply applications
2. AM (amplitude modulation) detectors
3. Back-EMF path
4. Clamping or DC restoration
5. Clipper or limiter
6. Non-linear circuits
7. Logic circuits

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What is PLC? How does it work? Distinguish SCADA & PLC controlled system.

What is PLC? 

The PLC (Programmable Logic Controller) is a small industrial computer usually found in factories. Its main use is to replace the relay logic of a plant or process. Today, the PLC is being used in SCADA systems to do its very good programmability. Earlier PLC’s have no serial communication ports for interfacing to radio for transferring of data. Nowadays, PLC's have extensive communication features and a wide support for popular radio units being used for SCADA system. In the near future we are seeing the merging of the RTUs(Remote Terminal Unit) and the PLC’s. 

What is SCADA? 

SCADA (Supervisory Control And Data Acquisition) system refers to the combination of telemetry and data acquisition. It consists of collecting information, transferring it back to a central site, carrying out necessary analysis and control, and then displaying this data on a number of operator screens. The SCADA system is used to monitor and control a plant or equipment. Control may be automatic or can be initiated by operator commands.   

Components of SCADA System 

Components of a SCADA System a SCADA system is composed of the following: 

1. Field Instrumentation 

2. Remote Stations 

3. Communications Network 

4. Central Monitoring Station 

SCADA & PLC 

Traditional PLC are migrating toward to traditional DCS for instants Fisher Delta V. For application in small or medium plant many people use a PLC (Allen Bradley) and also use DCS (Delta V, PlantScappe). If you have a small plant, it is better to set PLC or DCS system which has a system starting at 5 I/O and going up to 500 I/O. 

SCADA is just that supervisory and data acquisition. It usually is not in plant but it used to supervise multiple small sites. In industry SCDA often do monitoring systems with little RTU at each well site.

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How to convert electrical energy to infrared energy or to microwave energy?

To convert to IR, use an IR lamp, aka heat lamp. IR is heat energy.

 To convert to microwave, you need a magnetron and a high voltage power supply, as is found in a microwave oven. 

For the reverse, it is more difficult.

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What is the difference between a transformer, a converter and a power supply?

Transformer

A Transformer is an electrical device by which alternating current of one voltage is changed to another voltage using coils. There are several different types, but they all basically do the same thing - change the voltage. They are usually heavy for their size due to the weight of the coils (size and weight depends on their rating).

Converter

A Converter is an electronic device that is used in some cases instead of a transformer. The converter doesn’t actually lower the voltage, but rather delays each electrical cycle making the device think it is working with the proper voltage (does not produce an output of full sine wave electricity). If you were to measure with a voltmeter the output of the converter, it would actually measure 220V (in Israel). These converters are not to be used with any electronic devices, and I personally do not recommend using them with ANY device. Although they are sold for use with hair dryers, bottle warmers, irons, etc, I’ve seen too many of these appliances ruined when used with a converter.

Power Supply

In actual fact, anything that supplies power is a Power Supply. But usually when people talk about power supplies, they are talking about a device that not only lowers the voltage, but also converts AC (alternating current) to DC (direct current). These are what you find on many small electronic devices (walkman, cordless telephones, desk clocks…etc), looking like a small black box that gets plugged in the receptacle, and having a cord that plugs into whatever device you're using. If you come from the US with a device using a power supply of this type rated for 110V, simply buy the 220V equivalent here in Israel. They are relatively inexpensive and work exactly like their 110V cousin. Make sure to bring the 110V power pack with you so you can be sure of buying exactly what you need.

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Draw half & full wave rectifier showing input and output signals.

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