Thyristor Semiconductor Products Page 34 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1003 Figure AN1003.16 illustrates a circuit for phase controlling a permanent magnet (PM) motor. Since PM motors are also generators, they have characteristics that make them difficult for a standard Triac to commutate properly. Control of a PM motor is easily accomplished by using an alternistor Triac with enhanced commutating characteristics. DC MTR 115 V ac Input 1.5 A 3.3 k 250 k 15 k 1/2 W 0.1 F 400 V Diac Q4006LTH 100 0.1 F 100 V 0.1 F 400 V T MT1 MT2 + - Figure AN1003.16 Circuit for Phase Controlling a Permanent Magnet Motor Therefore, the alternistor Triac controller should be connected in series with the AC input side of the rectifier bridge. The possible alternative of putting an SCR controller in series with the motor on the DC side of the rectifier bridge can be a challenge when it comes to timing and delayed turn-on near the end of the half cycle. The alternistor Triac controller shown in Figure AN1003.16 offers a wide range control so that the alternistror Triac can be triggered at a small conduction angle or low motor speed; the rectifiers and alternistors should have similar voltage ratings, with all based on line voltage and actual motor load requirements. SCR Phase Control Figure AN1003.17 shows a very simple variable resistance half-wave circuit. It provides phase retard from essentially zero (SCR full on) to 90 electrical degrees of the anode voltage wave (SCR half on). Diode CR 1 blocks reverse gate voltage on the negative half-cycle of anode supply voltage. This protects the reverse gate junction of sensitive SCRs and keeps power dissipation low for gate resistors on the negative half cycle. The diode is rated to block at least the peak value of the AC supply voltage. The retard angle cannot be extended beyond the 90-degree point because the trigger circuit supply voltage and the trigger voltage producing the gate current to fire are in phase. At the peak of the AC supply voltage, the SCR can still be triggered with the maximum value of resistance between anode and gate. Since the SCR will trigger and latch into conduction the first time I GT is reached, its conduction cannot be delayed beyond 90 electrical degrees with this circuit. R 1 AC Input SCR 1 2.2 k R 3 R 2 CR 1 Load IN4003 IN4004 120 V ac 60 Hz 120 V ac 60 Hz 240 V ac 60 Hz 240 V ac 60 Hz 240 V ac 50Hz 0.8 A 8.5 A 0.8 A 8.5 A 2.5 A 500 k 100 k 1 M 250 k 1 M 1 k Not Required 1 k Not Required 1 k EC103D S4010R EC103D S6010R T106M1 R 2 R 3 SCR 1 CR 1 AC Input Voltage AC Load Current Figure AN1003.18 shows a half-wave phase control circuit using an SCR to control a universal motor. This circuit is better than simple resistance firing circuits because the phase-shifting characteristics of the RC network permit the firing of the SCR beyond the peak of the impressed voltage, resulting in small conduction angles and very slow speed. M R 1 R 2 C 1 D-30A SCR 1 Diac 3.3 k AC Supply Universal Motor CR 1 AC Input Voltage 120 V ac 60 Hz 240 V ac 60 Hz 240 V ac 50 Hz AC Load Current 8 A 6.5 A 6.5 A 150 k 200 k 200 k IN4003 IN4004 S6008L S4015L S6008L 0.1F 200 V 0.1F 400 V 0.1F 400 V R 2 CR 1 SCR 1 C 1 Figure AN1003.18 Half-wave Motor Control Permanent Magnet Motor Control Phase Control Using Thyristors (continued)

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