SMT50-62

Manufacturer Part NumberSMT50-62
ManufacturerLittelfuse, Inc.
SMT50-62 datasheet
 


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SMT50
ELECTRICAL CHARACTERISTICS
The electrical characteristics of a SMT50 device are similar to
that of a self-gated Triac, but the SMT50 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 SMT50 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 SMT50 is negligible and will
not affect the protected system.
When a transient occurs, the voltage across the SMT50 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
SELECTING A SMT50
1. When selecting a SMT50 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.
COMPLIES WITH THE
PEAK SURGE
FOLLOWING STANDARDS
VOLTAGE
(V)
(CCITT) ITU-K20
1000
(CCITT) ITU-K17
1500
VDE0433
2000
VDE0878
2000
IEC-1000-4-5
level 3
level 4
FCC Part 68, lightning surge
1500
type A
800
FCC Part 68, lightning surge
1000
type B
Bellcore TR-NWT-001089
2500
first level
1000
Bellcore TR-NWT-001089
5000
second level
CNET I31-24
1000
48
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 SMT50 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 SMT50 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.
V-I Graph illustrating symbols
and terms for the SMT50 surge
protection device.
VOLTAGE
CURRENT
ADMISSIBLE IPP
WAVEFORM
WAVEFORM
µS)
µS)
(
(
(A)
10/700
5/310
25
10/700
5/310
38
10/700
5/310
50
1.2/50
1/20
50
10/700
5/310
50
1.2/500
8/20
100
10/160
10/160
75
10/560
10/560
55
9/720
5/320
25
2/10
2/10
150
10/1000
10/1000
50
2/10
2/10
150
0.5/700
0.8/310
25
w w w . l i t t e l f u s e . c o m
I
I
pp
I
BO
I
H
I
RM
V
V
V
RM
BR
V
V
R
BO
NECESSARY
RESISTOR
(
)
-
-
-
-
-
-
12.5
6.5
-
11.5
10
11.5
-