NOVEMBER 1997 - REVISED FEBRUARY 2005

Specifications are subject to change without notice.

Customers should verify actual device performance in their specific applications.

Figure 9a shows a traditional overvoltage protection scheme for a high power switching thyristor, Th1. The protection voltage level is set by a

BOD (BreakOver Diode) thyristor. Potentially damaging voltage transients cause the BOD to crowbar which turns on thyristor Th1. The on state

of thyristor Th1 causes the current drawn by the load from the d.c. voltage supply +V to continuously increase until the fast acting fuse F1

operates.

Resistor R1 limits the peak BOD current and diode D1 protects the unidirectional BOD against reverse polarity voltage. Resistor R2 provides a

d.c. return, and with capacitor C1, forms a low pass network to prevent false triggering from noise. Further trigger voltage discrimination and

isolation is given by the series combination of zener diode D2 and reverse blocking diode D3. Capacitor C2 and Resistor R3 form the normal

snubber network for the thyristor Th1.

TISP3600F3, TISP3700F3

APPLICATIONS INFORMATION

BOD Replacement

Figure 9b shows the TISP3x00F3 replacing the unidirectional BOD and reverse polarity protection diode, D1. Reverse polarity protection is not

needed for the TISP3x00F3 as it is bidirectional.

Figure 9. Thyristor Protection

n

C1

D1

BOD

D2

D3

R1

R2

C2

R3

LOAD

F1

Th1

GATE

DRIVE

C1

TISP

3x00F3

D2

D3

R1

R2

C2

R3

LOAD

F1

Th1

GATE

DRIVE

+V

+V

a)

b)

AI3XAA

IEEE Std 802.3, 2000 Edition (IEEE Standard for Information technology— Telecommunications and information exchange between systems—

Local and metropolitan area networks— Specific requirements, Part 3: Carrier sense multiple access with collision detection (CSMA/CD)

access method and physical layer specifications) specifies three network insulation withstands: 1.5 kV rms a.c., 2.25 kV d.c. and 2.4 kV 1.2/50

impulse. Under these conditions there shall be no insulation breakdown, as defined in IEC 60950:1991. Also, there is a 2 MΩ insulation

resistance minimum requirement measured at 500 V d.c. (250 µA maximum).

LAN System Insulation Protection (continued)