R3612 Datasheet, PDF (10/16 Pages) Power Innovations Ltd – PROGRAMMABLE OVERVOLTAGE PROTECTOR FOR ERICSSON COMPONENTS 3357/3 DCLIC

R3612
PROGRAMMABLE OVERVOLTAGE PROTECTOR
FOR ERICSSON COMPONENTS 3357/3 DCLIC
DECEMBER 1995 - REVISED SEPTEMBER 1997
0
-20
V_K
-40
V_GG
-60
-80
0.0
0.5
1.0
1.5
Time - µs
1
I_G
0
-1
-2
I_K
-3
-4
-5
0.0
0.5
1.0
1.5
Time - µs
Figure 5. PROTECTOR FAST IMPULSE CLAMPING AND SWITCHING WAVEFORMS
voltage, V_GG. This increase does not directly add to the protection voltage as the supply voltage change
reaches a maximum as the gate current reverses polarity; whereas the protection voltage peaks earlier than
this. In Figure 5, the peak clamping voltage (V_(BO)) is -77.5 V, an increase of 5.5 V on the nominal gate supply
voltage. This 5.5 V increase is the sum of the supply rail increase, (0.04 V), and the protection circuits
cathode diode to supply rail breakover voltage (5.46 V). In practice, the gate decoupling capacitor would be
about 80% smaller (e.g. 200 nF), giving a five times increase in supply voltage (5*0.04 = 0.2 V) and a V_(BO)
value of about -77.7 V.
Figure 5 shows the thyristor waveforms under a high impedance power cross condition. Positive half cycles
are clamped to ground by the diodes D1 and D2, producing a peak current of 350 mA. Negative half cycles
are clamped to the -70 V gate supply voltage. The peak cathode current of 120 mA is not enough to cause
thyristor switching. As the thyristor first starts to conduct, the cathode and gate currents are the same. (I_K =
I_G). At about 70 mA the thyristor starts to become active and anode current starts to flow. The increasing
anode current progressively reduces the gate current, until the gate current is nearly zero at 15 ms. After that,
PRODUCT INFORMATION
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