Thyristor Semiconductor Products Page 26 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1002 Holding Current of SCRs and Triacs Time Holding Current Point Zero Crossing Point Principal Current Through Thyristor Gate Pulse Gate Drive to Thyristor Latching Current Point 2.0 1.5 1.0 .5 0 -40 -15 +25 +65 +100 Case Temperature (T C ) - C Ratio of I H I H (T C = 25 C) INITIAL ON-STATE CURRENT = 200 mA dc Relationship of Gating, Latching, and Holding Currents Figure AN1002.7 Typical DC Holding Current vs Case Temperatures Similar to gating, latching current requirements for Triacs are different for each operating mode (quadrant). Definitions of latching modes (quadrants) are the same as gating modes. Therefore, definitions shown in Figure AN1002.2 and Figure AN1002.3 can be used to describe latching modes (quadrants) as well. The following table shows how different latching modes (quadrants) relate to each other. As previously stated, Quadrant II has the lowest latching current sensitivity of all four operating quadrants. Figure AN1002.6 Latching and Holding Characteristics of Thyristor I L (in given Quadrant) Typical Ratio of ------------------------------------------ at 25 O C I L (Quadrant 1) Type Operating Mode Quadrant I Quadrant II Quadrant III Quadrant IV 4 A Triac 1 4 1.2 1.1 10 A Triac 1 4 1.1 1 Example of a 4 Amp Triac: If I L (I) = 10 mA, then I L (II) = 40 mA I L (III) = 12 mA I L (IV) = 11 mA Latching current has even somewhat greater temperature dependence compared to the DC gate trigger current. Applications with low temperature requirements should have sufficient principal current (anode current) available to ensure Thyristor latch-on. Two key test conditions on latching current specifications are gate drive and available principal (anode) current durations. Shortening the gate drive duration can result in higher latching current values. Holding current (I H ) is the minimum principal current required to maintain the Thyristor in the on state. Holding current can best be understood by relating it to the "drop- AN1002.6 shows the sequences of gate, latching, and holding currents. Holding current will always be less than closer the holding current value approaches its latching current value. Holding current is independent of gating and latching, but the device must be fully latched on before a holding current limit can be determined.Holding current modes of the Thyristor are strictly related to the voltage polarity across the main terminals. The following table illustrates how the positive and negative holding current modes of Triacs relate to each other. Typical Triac Holding Current Ratio Type Operating Mode I H (+) I H (-) 4 A Triac 1 1.1 10 A Triac 1 1.3 Example of a 10 A Triac: If I H (+) = 10 mA, then I H (-) = 13 mA Holding current is also temperature-dependent like gating and latching shown in Figure AN1002.7. The initial on- state current is 200 mA to ensure that the Thyristor is fully latched on prior to holding current measurement. Again, applications with low temperature requirements should have sufficient principal (anode) current available to maintain the Thyristor in the on-state condition. Both minimum and maximum holding current specifications may be important, depending on application. Maximum holding current must be considered if the Thyristor is to stay in conduction at low principal (anode) current; the minimum holding current must be considered if the device is expected to turn off at a low principal (anode) current. Example of a 10 A Triac: If I H (+) = 10 mA at 25 C, then I H (+) 7.5 mA at 65 C Although gating, latching, and holding currents are independent of each other in some ways, the parameter values are related. If gating is very sensitive, latching and holding will also be very sensitive and vice versa. One way to obtain a sensitive gate and not-so-sensitive latching- shown in Figure AN1002.8. Gating, Latching, and Holding of SCRs and Triacs (continued)

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