Silicon Controlled Rectifiers
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An SCR is made of Silicon.
When SCR starts conducting, then Gate loses all control.
An SCR is a Current triggered device. *Memorize
An SCR can exercise control over positive half cycles of ac supply. *Memorize
IN the normal operation of the SCR, anode is positive with respect to cathode.
An SCR has three pn junctions.
In normal operation of an SCR, gate is positive with respect to cathode. *Unsure
An SCR behaves as a Unidirectional switch.
An SCR is a solid state equivalent of Gas-Filled Triode.
In an SCR circuit, the angle of conduction can be changed by Changing Gate Voltage.
The normal way to turn on a SCR is by Appropriate Gate Current.
An SCR is turned off by Reducing anode voltage to zero. *Memorize
If firing angle in an SCR circuit is increased, the output is decreased. *Memorize
When an SCR is turned on, the voltage across it is about 1 V. *Memorize
The control element of an SCR is Gate.
An SCR has three terminals which are Cathode, Anode, Gate.
An SCR is made of silicon and not germanium because silicon is small leakage current.
We can control ac power in a load by connecting 2 SCRs in parallel opposition.
In an SCR circuit, the supply voltage is generally less than that of breakover voltage. *Memorize
An SCR is turned off when Anode current is reduced to zero,
If gate current is increased, then anode-voltage at which SCR closes is decreased. *Memorize
When SCR is OFF, the current in the circuit is small leakage current.
An SCR is sometimes called Thyristor.
An SCR has four semiconductor layers.
An SCR combines the features of rectifier and transistor.
Regulated DC Power Supply
1. A Zener voltage regulator will cease to act as a voltage regulator if Zener current becomes Zero.
*Unsure
2. If the load resistance decreases in a Zener regulator, then Zener current decreases,
3. A Zener regulator decreases the ripple in the power supply.
4. Zener diode are generally made of silicon.
5. In an unregulated power supply, if load current increases, the output voltage decreases.
6. If the load current drawn by unregulated power supply increases, the dc output voltage
decreases.
7. A 30 V Zener will have depletion layer width more than that of 10 V Zener.
8. A Zener voltage regulator is used for small load currents. *Memorize
9. A Zener diode that has very narrow depletion layer will experience Zener breakdown by
mechanism. *Memorize correct
10. In a Zener voltage regulator, the changes in load current produce changes in Zener current.
*Memorize correct
11. Two similar 15 V Zener diodes are connected in series. What is the regulated output voltage? 30
V
12. An ideal regulated power supply is one which has voltage regulation of 0%.
13. If the input ac voltage to regulated or ordinary power supply increases by 5%, what will be the
approximate change in dc output voltage? 5%.
14. The load voltage is approximately constant when a Zener diode is reverse biased,
15. A power supply has a voltage regulation of 1%. If the no-load voltage is 20 V, what is the full load
voltage? 8 V **how??
16. In a regulated power supply, two similar 15 V Zener diodes are connected in series. The input
voltage is 45 Vdc. If each Zener has a maximum current rating of 300 mA, what should be the
value of the series resistance? 50 ohms
17. As the junction temperature increases, the voltage breakdown point for Zener mechanism is
decreased. *Memorize
18. As the junction temperature increases, the voltage breakdown point for avalanche mechanism
increases.
19. For increasing the voltage rating, Zener diodes are connected in series.
20. When load current is zero, the Zener current will be maximum. *Memorize
21. A Zener diode acts like a battery in the breakdown region.
22. The rupture of covalent bonds will occur when the electric field is more than 10^5 V/cm.
*Memorize
23. What is true about the breakdown voltage in a Zener diode? It is approximately constant.
24. A Zener diode is used as a shunt voltage regulator device.
25. A power supply which has a voltage regulation of 10% is unregulated power supply.
26. Commercial power supplies have voltage regulation within 1%. *Understand
27. If the doping level is increased, the breakdown voltage of the Zener is decreased.
28. Another name for Zener diode is Breakdown diode. *Memorize
29. The current in a Zener diode is limited by External resistance and Power dissipation.
30. The Zener current will be minimum when Load current is maximum.
31. Which of these is the best description for a Zener diode? Constant voltage device.
32. In a 15 V Zener diode, the breakdown mechanism will occur by