Engr. Mary Charlemaine Abas, MECE THYRISTORS
Typical Packaging of THYRISTORS
Intended Learning Outcome • Analyze the characteristics, operations, and circuit implementations of Thyristors. Specifically the following: o Shockley Diode o SCR o SCS o DIAC o TRIAC o UJT o PUT o Other solid-state devices used as Triggers o Phase Control o Other Control applications
What is THYRISTOR?
What is THYRISTOR?
Applications of Thyristor • Light dimmers • Power-switching circuit • Relays • Logic circuits • Heaters • Welders • Battery chargers • DC and AC motor speed controls • Voltage regulators
SHOCKLEY DIODE • Constructed of 4 pnpn semiconductor layer.
SHOCKLEY DIODE Basic Construction Equivalent Circuit Symbol
Basic Operation of SHOCKLEY DIODE • FB: – open switch at Forward Blocking region ( very high forward Resistance) = OFF state where V AK = 0 V up to a value of FORWARD-BREAKOVER VOLTAGE V BR(F).
Basic Operation of SHOCKLEY DIODE • FB: – As I A = I S, V AK = V BR(F) . – V AK drops and diode enters to Forward Conduction region – closed switch or ON state as long as I A > I H .
SHOCKLEY DIODE • HOLDING CURRENT (I H ) – Minimum forward current required to maintain conduction. • SWITCHING CURRENT (I S ) – Value of the anode current at the point where the device switches from forward-blocking (OFF) to forward-conduction region (ON). – Always less than the I H.
SHOCKLEY DIODE • Once I A drops below I H until I S , the device is driven back into cutoff. • When V AK reaches forward breakover voltage: The device current I A rapidly increase as the device is driven into saturation. Breakover-refers to the way a thyristor breaks down and then immediately goes into saturation. (increasing VCC breaks down either Q1 or Q2 and drives both transistors into saturation.
A certain diode is biased in the forward-blocking region with an anode-to-cathode voltage of 20V. Under this bias condition, the anode current is 1μA. Determine the resistance of the diode in the forward-blocking region.
Determine the value of anode current when the device is on. VBR(F) = 10V. Assume the forward voltage drop is 0.9V.
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- Spring '20