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LB1201AB Datasheet(PDF) 6 Page - Power Innovations Ltd |
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LB1201AB Datasheet(HTML) 6 Page - Power Innovations Ltd |
6 / 14 page TISP61060D, TISP61060P DUAL FORWARD-CONDUCTING P-GATE THYRISTORS PROGRAMMABLE OVERVOLTAGE PROTECTORS 6 SEPTEMBER 1995 - REVISED SEPTEMBER 1997 PRODUCT INFORMATION ic based protectors In 1986, an IC based gated protector was proposed (A 90 V Switching Regulator and Lightning Protection Chip Set, Robert K. Chen, Thomas H. Lerch, Johnathan S. Radovsky, D. Alan Spires, IEEE Solid-State Circuits Conference, February 20, 1986, pp 178/9 and pp 340/1). Commercially, this resulted in the AT&T Microelectronics LB1201AB device and the higher current Texas Instruments Inc. TCM1060 device This implementation consisted of four diodes and two high holding current thyristors. Positive overvoltages on the line wires are clipped to ground by forward conduction of the wire to ground diodes. Negative overvoltages are initially clipped close to the SLIC negative supply rail, VBAT, by conduction of the thyristor cathode-gate and gate series diode. This means that the protection voltage level for slow wave forms will be about 1.5 V lower than the SLIC supply voltage. If sufficient current is available from the overvoltage, then the thyristor will switch into a low voltage on-state condition. When the thyristor crowbars, the two series gate diodes prevent the SLIC supply from being shorted to ground via the thyristor gate. As the overvoltage subsides the high holding current of the crowbar prevents d.c. latchup (see Figure 1). impulse protection performance The impulse protection voltage will be the sum of the gate supply (VBAT) and the impulse peak gate-cathode voltage (VGK(BO)). Capacitor C1 provides the pulse of gate current that occurs during fast rising impulses. The protection voltage will be increased if there is a long connection between the gate decoupling capacitor, C1, and the gate terminal. During the initial rise of a fast impulse (e.g. 2/10), the gate current (IG) is the same as the cathode current (IK). Rates of 70 A/µs can cause inductive voltages of 0.7 V in 2.5 cm of printed wiring track. To minimise this inductive voltage increase of protection voltage, the length of the capacitor to gate terminal tracking should be minimised. Inductive voltages in the protector cathode wiring can increase the protection voltage. These voltages can be minimised by routing the SLIC connection through the protector as shown in Figure 2. a.c. protection performance Figure 2 shows a typical a.c. power cross test circuit. A variable voltage a.c. source is applied to the line card via 600 Ω series resistors. On the line card there are further series resistors R1 and R2. These resistors provide over-current protection by fusing or going high resistance under high current a.c. conditions. Figure 3 shows the gate and cathode a.c. power line cross voltage and current wave forms of the IC based protector. Positive voltages are clipped at about +1 V by diode conduction. Negative voltages are clipped to about -52 V as the SLIC supply voltage was -50 V. Sufficient current (200 mA) was available to cause the Figure 2. SIMPLIFIED IC BASED SLIC PROTECTOR CIRCUIT R1 50 Ω Ω RING WIRE TIP WIRE Th4 Th5 SLIC IC BASED SLIC PROTECTOR V BAT C1 100 nF AI6XAD 600 Ω Ω 600 Ω Ω A.C. GENERATOR 0 - 600 Vrms SWITCHING MODE POWER SUPPLY GENERATOR SOURCE RESISTANCE I BAT I G I SLIC C2 D1 D2 Tx R2 50 Ω Ω |
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