Thyristor Semiconductor Products Page 71 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1007 UAA2016 Supply Voltage Sync 220 V ac R S 1 8 5 4 3 2 V EE Pulse Amplifier Internal Reference Sampling Full Wave Logic R sync V ref Synchronization 11-Bit Counter 1/2 + 4-Bit DAC Output R out +V CC C F 6 7 - Failsafe + R def R 2 R 1 R 3 R S S2 S1 Hys Adj Temp. Red. Sense Input Load NTC Figure AN1007.12 Heater Control Schematic R out according to the Triac maximum gate current (I GT ) and the application low temperature limit. For a 2 kw load at 220 V rms, a good Triac choice is Q6012LH5. Its maximum peak gate trigger current at 25 C is 50 mA. out should be 68 . since I GT minimum current output from UAA2016 pin 6 is -90 mA at -8 V, -20 C. Output Pulse Width, R sync Figure AN1007.13 shows the output pulse width T P determined by the Triac's I H , I L together with the load value, characteristics, and working conditions (frequency and voltage). AC Line Waveform I L I H T P T P is centered on the zero-crossing. Gate Current Pulse Figure AN1007.13 Zero Voltage Technique To ensure best latching, T P should be 200 s, which means R sync . To ensure best latching, T P should be 200 s, which means R sync . R S and Filter Capacitor (C F ) For better UAA2016 power supply, typical value for R S could be 27 k , 2 W with C F Summary of Zero Crossing Turn-on Circuits Zero voltage crossing turn-on opto-drivers are designed to limit turn-on voltage to less than 20 V. This reduces the amount of RFI and EMI generated when the Thyristor switches on. Because of this zero turn-on, these devices cannot be used to phase control loads. Therefore, speed control of a motor and dimming of a lamp cannot be accomplished with zero turn-on opto-couplers. Since the voltage is limited to 20 V or less, the series gate resistor that limits the gate drive current has to be much lower with a zero crossing opto-driver. With typical inhibit voltage of 5 V, an alternistor Triac gate could require a 160 mA at -30 C (5 V/0.16 A = 31 gate resistor). If the load has a high inrush current, then drive the gate of the Triac with as much current as reliably possible but stay under the I TSM rating of the opto-driver. By using 22 for the gate resistor, a current of at least 227 mA is supplied with only 5 V, but limited to 909 mA if the voltage goes to 20 V. As shown in Figure AN1007.14, Figure AN1007.15, and Figure AN1007.16, a 22 gate resistor is a good choice for various zero crossing controllers. Thyristors Used as AC Static Switches and Relays (continued)

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