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March 17, 2017

What is the difference between Electric Motor and Electric Generator?

Difference between Electric Motor and Electric Generator: 

  • Generator converts mechanical energy to electrical energy, while motor converts mechanical energy to electrical energy. 
  • In a generator, shaft attached to the rotor is driven by a mechanical force and electric current is produced in the armature windings, while the shaft of a motor is driven by the magnetic forces developed between the armature and field; current has to be supplied to the armature winding. 
  • Motors (generally a moving charge in a magnetic field) obey the Fleming`s left hand rule, while the generator obeys Fleming’s left hand rule. 



March 14, 2017

What are the Advantages of Integrated Circuits (ICs)?

Advantages of Integrated Circuits:

The major advantages of integrated circuits over those made by interconnecting discrete components are as follows:
  1. Extremely small size – Thousands times smaller than discrete circuits. It is because of fabrication of various circuit elements in a single chip of semiconductor material.
  2. Very small weight owing to miniaturised circuit.
  3. Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. Owing to mass production of an IC costs as much as an individual transistor.
  4. More reliable because of elimination of soldered joints and need for fewer interconnections.
  5. Lower power consumption because of their smaller size.
  6. Easy replacement as it is more economical to replace them than to repair them.
  7. Increased operating speed because of absence of parasitic capacitance effect.
  8. Close matching of components and temperature coefficients because of bulk production in batches.
  9. Improved functional performance as more complex circuits can be fabricated for achieving better characteristics.
  10. Greater ability of operating at extreme temperatures.
  11. Suitable for small signal operation because of no chance of stray electrical pickup as various components of an INC are located very close to each other on a silicon wafer.
  12. No component project above the chip surface in an INC as all the components are formed within the chip.

What are the limitations of integrated circuits?

The integrated circuits have few limitations also, as listed below:

  1. In an IC the various components are part of a small semi-conductor and the individual component or components cannot be removed, replaced, therefore, if any component in an IC fails, the whole IC has replaced by the new one. 
  2. Limited power rating as it is not possible to manufacture high power greater than 10 Watt) ICs.
  3. Need of connecting inductors and transformers exterior to the conductor chip as it is not possible to fabricate inductors and transform on the semi-conductor chip surface. 
  4. Operations at low voltage as ICs function at fairly low voltage.
  5. Quite delicate in handling as these cannot withstand rough handling or excessive heat. 
  6. Need of connecting capacitor exterior to the semi-conductor chip as it is neither convenient nor economical to fabricate capacitances exceeding 30pF. Therefore, for higher values of capacitance, discrete components, exterior to IC chip are connected. 
  7. High grade P-N-P assembly is not possible.
  8. Low temperature coefficient is difficult to be achieved.
  9. Difficult to fabricate an IC with low noise.
  10. Large value of saturation resistance of transistors.
  11. Voltage dependence of resistors and capacitors.
  12. The diffusion processes and other related procedures used in the fabrication process are not good enough to permit a precise control of the parameter values for the circuit elements. However, control of the ratios is at a sufficiently acceptable level. 

What is Schmitt trigger? How it works? Where is it used?

Schmitt trigger:

Schmitt trigger is an electronic circuit with positive feedback which holds the output level till the input signal to the comparator is higher than the threshold. It converts a sinusoidal or any analog signal to digital signal. It exhibits hysteresis by which the output transition from high to low and low to high will occur at different thresholds.

Invention:

The Schmitt trigger was invented by American scientist Otto H. Schmitt in 1934. By that time, Otto Schmitt was a student. In the year 1937, he published his invention in his doctoral. The name he gave was "thermionic trigger".

Schmitt Trigger Types:

The two different Schmitt trigger types are:
  1. Non-inverting type, in which the input and output are both high / both low at the same time (no phase shift).
  2. Inverting type, in which there is 180° phase shift between input and output.


Symbols:

There are basically two symbols for the Schmitt Trigger. The symbol is a triangle with an input and an output, just like the one used for the non-inverting buffers. Inside there is the hysteresis symbol. Depending on the type of Schmitt Trigger, inverting or non-inverting (standard), the hysteresis curve sign differs.

Figure 1: Logic Symbols of Schimitt Trigger.

Operations of Schimitt Trigger:

The Schmitt Trigger is a type of comparator with two different threshold voltage levels. Whenever the input voltage goes over the High Threshold Level, the output of the comparator is switched HIGH (if is a standard ST) or LOW (if is an inverting ST). The output will remain in this state, as long as the input voltage is above the second threshold level, the Low Threshold Level. When the input voltage goes below this level, the output of the Schmitt Trigger will switch.

The HIGH and LOW output voltages are actually the POSITIVE and NEGATIVE power supply voltages of the comparator. The comparator needs to have positive and negative power supply (like + and -) to operate as a Schmitt Trigger normally. The following drawing shows how a Schmitt Trigger would react to an AC voltage input:

Figure 2: Basic operation of a Schimitt Trigger.

The orange line is the AC input. The horizontal RED line indicates the High Threshold Level, while the BLUE horizontal line indicates the Low Threshold Level. The green line is the output of the Schmitt Trigger. When the input voltage level goes above the High Threshold Level, then the output of the ST goes High. When the input voltage level goes below the Low Threshold Level, then the output of the ST goes Low. This is the basic operation of a Schmitt Trigger.

Figure 3: The most simple Schmitt Trigger circuit is implemented with a comparator with a positive feedback.

Applications of Schimitt Trigger:  


March 11, 2017

Why should Dry-Type Transformers never be overloaded?

Overloading of a transformer results in excessive temperature. This excessive temperature causes overheating which will result in rapid deterioration of the insulation and cause complete failure of the transformer coils.

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