Thyristor Semiconductor Products Page 77 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1008 I GT : DC Gate Trigger Current SCR I GT the Thyristor to switch from the non-conducting to the conducting state for a specified load voltage and current as well as case temperature. The characteristic curve illustrated in Figure AN1008.6 shows that trigger current is temperature dependent. The Thyristor becomes less sensitive (requires more gate current) with decreasing junction temperatures. The gate current should be increased by a factor of two to five times the minimum threshold DC trigger current for best operation. Where fast turn-on is demanded and high di/dt is present or low temperatures are expected, the gate pulse may be 10 times the minimum IGT, plus it must be fast-rising and of sufficient duration in order to properly turn on the Thyristor. 0 1.0 2.0 3.0 4.0 -65 -15 +65 +25 +125 -40 Junction Temperature (T J ) - C Ratio of I GT I GT (T J = 25 C) Figure AN1008.6 Normalized DC Gate Trigger Current for All Quadrants versus Case Temperature Triac The description for the SCR applies as well to the Triac with the addition that the Triac can be fired in four possible modes (Figure AN1008.7): Quadrant I (main terminal 2 positive, gate positive) Quadrant II (main terminal 2 positive, gate negative) Quadrant III (main terminal 2 negative, gate negative) Quadrant IV (main terminal 2 negative, gate positive) MT2 POSITIVE (Positive Half Cycle) MT2 NEGATIVE (Negative Half Cycle) MT1 MT2 + I GT REF QII MT1 I GT GATE MT2 REF MT1 MT2 REF MT1 MT2 REF QI QIV QIII ALL POLARITIES ARE REFERENCED TO MT1 (-) I GT GATE (+) I GT - I GT GATE (-) I GT GATE (+) + - NOTE: Alternistors will not operate in Q IV Figure AN1008.7 Definition of Operating Quadrants V GT : DC Gate Trigger Voltage SCR V GT is the DC gate-cathode voltage that is present just prior to triggering when the gate current equals the DC trigger current. As shown in the characteristic curve in Figure AN1008.8, the gate trigger voltage is higher at lower temperatures. The gate-cathode voltage drop can be higher than the DC trigger level if the gate is driven by a current higher than the trigger current. Triac The difference in V GT for the SCR and the Triac is that the Triac can be fired in four possible modes. The threshold trigger voltage can be slightly different, depending on which of the four operating modes is actually used. 0 .5 1.0 1.5 2.0 -65 -15 +65 +25 +125 -40 Junction Temperature (T ) - C V (T = 25 C) Ratio of V Figure AN1008.8 Normalized DC Gate Trigger Voltage for All Quadrants versus Case Temperature I L : Latching Current SCR Latching current is the DC anode current above which the gate signal can be withdrawn and the device stays on. It is related to, has the same temperature dependence as, and is somewhat greater than the DC gate trigger current. (Figure AN1008.1 and Figure AN1008.2) Latching current is at least equal to or much greater than the holding current, depending on the Thyristor type. Latching current is greater for fast-rise-time anode currents since not all of the chip/die is in conduction. It is this dynamic latching current that determines whether a device will stay on when the gate signal is replaced with very short gate pulses. The dynamic latching current varies with the magnitude of the gate drive current and pulse duration. In some circuits, the anode current may oscillate and drop back below the holding level or may even go negative; hence, the unit may turn off and not latch if the gate signal is removed too quickly. Triac The description of this characteristic for the Triac is the same as for the SCR, with the addition that the Triac can be latched on in four possible modes (quadrants). Also, the required latching is significantly different depending on which gating quadrants are used. Figure AN1008.9 illustrates typical latching current requirements for the four possible quadrants of operation. Explanation of Maximum Ratings and Characteristics for Thyristors (continued)

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