TISP61089A
DUAL FORWARD-CONDUCTING P-GATE THYRISTORS
PROGRAMMABLE OVERVOLTAGE PROTECTORS
JUNE 1999
TIP
WIRE
600
Ω
GENERATOR
SOURCE
RESISTANCE
600
Ω
RING
WIRE
A.C.
GENERATOR
0 - 600 Vrms
R2
50
Ω
R1
50
Ω
TISP61089A
Th4
SLIC
Th5
SWITCHING MODE
POWER SUPPLY
Tx
I
G
C1
220 nF
I
SLIC
I
BAT
V
BAT
C2
D1
AI6XAGA
Figure 3. TISP61089A BUFFERED GATE PROTECTOR (SECTION 4.5.12 TESTING CONDITION)
operation of gated protectors
Figures 4. and 5. show how the TISP61089A limits negative and positive overvoltages. Positive overvoltages
ground. Negative overvoltages (Figure 4.) are initially clipped close to the SLIC negative supply rail value
(V
BAT
). If sufficient current is available from the overvoltage, then the protector (Th5) will crowbar into a low
voltage on-state condition. As the overvoltage subsides the high holding current of the crowbar prevents d.c.
latchup. The protection voltage will be the sum of the gate supply (V
BAT
) and the peak gate-cathode voltage
(V
GK(BO)
). 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, the gate current (I
G
) is the same
as the cathode current (I
K
). 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 will also increase the
protection voltage. These voltages can be minimised by routing the SLIC connection through the protector as
shown in Figure 3.
SLIC
PROTECTOR
SLIC
PROTECTOR
SLIC
SLIC
I
K
Th5
TISP
61089A
C1
220 nF
I
G
V
BAT
I
F
Th5
TISP
61089A
C1
220 nF
V
BAT
AI6XAHA
AI6XAIA
Figure 4. NEGATIVE OVERVOLTAGE CONDITION
Figure 5. POSITIVE OVERVOLTAGE CONDITION
PRODUCT
6
INFORMATION
POINN [ POWER INNOVATIONS LTD ]
