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Thyristors
25 questions By Tony R. Kuphaldt
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Question 13 of 25
Explain what a crowbar circuit is, and how it employs an SCR to protect a circuit from excessive voltage.
Reveal answerA “crowbar” circuit uses an SCR to clamp the output voltage of a DC power supply in the event of accidental overvoltage, in the same manner that a (literal) metal crowbar thrown across the terminals of a power supply would forcibly clamp the output voltage.
Notes:Discuss with your students whether or not they think a crowbar circuit is the sort of mechanism that sees regular use, or whether it is seldom activated.
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Question 14 of 25
What is a quadrac, and how does it differ from a regular TRIAC?
Reveal answerA “quadrac” is a TRIAC with a DIAC built-in, connected in series with the gate terminal.
Notes:Ask your students what benefit a quadrac would be over a regular TRIAC.
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Question 15 of 25
A student of electronics has just recently learned how to build audio amplifier circuits, and this inspires dreams of designing a super-powerful amplifier for a home entertainment system. One day, this student comes across a donation of electronic components from a local business, and in this donation are several industrial SCRs, rated at 20 amps each.
“Wow,” says the student, “these components look like really big transistors, but they’re rated for a lot of current. I could build a huge amplifier with these!”
The student approaches you for advice, because you’ve just recently learned how SCRs function in your electronics class. What do you tell the student, concerning the use of SCRs as audio amplification devices? How do you explain to this excited student that these devices will not work in an amplifier circuit?
Reveal answerI’ll let you determine the reason why SCRs cannot be used as audio amplification devices.
Notes:Believe it or not, I was once approached by an enthusiastic student with this very question!
Can someone please explain why do we need C1 capacitor in question 22 ? Circuit behaves exactly the same without it and I am confused about it’s purpose.