LITTELFUSE SMT100-120, SMT100-140, SMT100-200, SMT100-230, SMT100-270 Datasheet

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LITTELFUSE SMT100-120, SMT100-140, SMT100-200, SMT100-230, SMT100-270 Datasheet

SMT100

ELECTRICAL CHARACTERISTICS

The electrical characteristics of a SMT100 device are similar to that of a self-gated Triac, but the SMT100 is a two terminal device with no gate. The gate function is achieved by an internal current controlled mechanism.

Like the T.V.S. diodes, the SMT100 has a standoff voltage (Vrm) which should be equal to or greater than the operating voltage of the system to be protected. At this voltage (Vrm) the current consumption of the SMT100 is negligible and will not affect the protected system.

When a transient occurs, the voltage across the SMT100 will increase until the breakdown voltage (Vbr) is reached. At this point the device will operate in a similar way to a T.V.S. device and is in avalanche mode.

The voltage of the transient will now be limited and will only increase by a few volts as the device diverts more current. As this transient current rises, a level of current through the

device is reached (Ibo) which causes the device to switch to a fully conductive state such that the voltage across the device is now only a few volts (Vt). The voltage at which the device switched from the avalanche mode to the fully conductive state (Vt) is known as the Breakover voltage (Vbo). When the device is in the Vt state, high currents can be diverted without damage to the SMT100 due to the low voltage across the device, since the limiting factor in such devices is dissipated power (V x I).

Resetting of the device to the non-conducting state is controlled by the current flowing through the device. When the current falls below a certain value, known as the Holding Current (Ih), the device resets automatically.

As with the avalanche T.V.S. device, if the SMT100 is subjected to a surge current which is beyond its maximum rating, then the device will fail in short circuit mode, ensuring that the equipment is ultimately protected.

SELECTING A SMT100

1.When selecting a SMT100 device, it is important that the Vrm of the device is equal to or greater than the the operating voltage of the system.

2.The minimum Holding Current (Ih) must be greater than the current the system is capable of delivering otherwise the device will remain conducting following a transient condition.

V-I Graph illustrating symbols and terms for the SMT100 surge protection device

I

Ipp

IBO

IH

IRM

V

 

VRM VBR

VR VBO

 

COMPLIES WITH THE

 

PEAK SURGE

 

VOLTAGE

 

CURRENT

 

ADMISSIBLE IPP

 

NECESSARY

 

 

 

 

 

 

 

FOLLOWING STANDARDS

 

VOLTAGE

 

WAVEFORM

 

WAVEFORM

 

 

 

RESISTOR

 

 

 

(V)

 

( S)

 

( S)

 

(A)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(CCITT) ITU-K20

 

1000

 

10/700

 

5/310

 

25

 

-

 

 

(CCITT) ITU-K17

 

1500

 

10/700

 

5/310

 

38

 

-

 

 

VDE0433

 

2000

 

10/700

 

5/310

 

50

 

-

 

 

VDE0878

 

2000

 

1.2/50

 

1/20

 

50

 

-

 

 

IEC-1000-4-5

 

level 3

 

10/700

 

5/310

 

50

 

-

 

 

 

 

level 4

 

1.2/500

 

8/20

 

100

 

-

 

 

FCC Part 68, lightning surge

 

1500

 

10/160

 

10/160

 

75

 

12.5

 

 

type A

 

800

 

10/560

 

10/560

 

55

 

6.5

 

 

FCC Part 68, lightning surge

 

1000

 

9/720

 

5/320

 

25

 

-

 

 

type B

 

 

 

 

 

 

 

 

 

 

 

 

Bellcore TR-NWT-001089

 

2500

 

2/10

 

2/10

 

150

 

11.5

 

 

first level

 

1000

 

10/1000

 

10/1000

 

50

 

10

 

 

Bellcore TR-NWT-001089

 

5000

 

2/10

 

2/10

 

150

 

11.5

 

 

second level

 

 

 

 

 

 

 

 

 

 

 

 

CNET I31-24

 

1000

 

0.5/700

 

0.8/310

 

25

 

-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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