Thyristors (AC & DC)

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Conditions under which a thyristor begins to conduct
Sufficient Gate current & sufficient Gate voltage
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Conditions to maintain thyristor conduction
Sufficient holding current
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Give 1 advantage of a thyristor over a relay
A thyristor is not prone to mechanical wear like relays are
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Give 1 advantage of a thyristor over a transistor
Tiny linear region to dissipate power vs transistor large linear region
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Give 1 advantage of a thyristor over a FET
No Rdson to cause power dissipation as conducting
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Give 1 potential disadvantage of thyristors
They latch on until the holding current drops
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How should the issue of latching be solved?
Capacitor Commutation
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How does Capacitor Commutation work?
The Voltage on the capacitor drops, causing the voltage between the load and the thyristor to temporarily drop to -Vs. This reverse-biases the thyristor, switching it off.
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How do you change the average voltage into a load in an AC circuit?
Sine wave 'modulation' - control where in the cycle the thyristor switches on
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How do you alter the switch-on point of the thyristor?
Using an RC circuit to change the phase of the gate current
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What is the purpose of the Diac in the phase control circuit?
Makes the switch-on point more stable
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Other cards in this set

Card 2

Front

Sufficient holding current

Back

Conditions to maintain thyristor conduction

Card 3

Front

A thyristor is not prone to mechanical wear like relays are

Back

Preview of the back of card 3

Card 4

Front

Tiny linear region to dissipate power vs transistor large linear region

Back

Preview of the back of card 4

Card 5

Front

No Rdson to cause power dissipation as conducting

Back

Preview of the back of card 5
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