NP−SBMC Series
100
10
1
t = rise time to peak value
t = decay time to half value
f
r
Peak
Value
100
Half Value
50
0
0t
r
t
f
0.1
1
10
100
1000
CURRENT DURATION (s)
TIME (ms)
Figure 2. Nonrepetitive On−State Current vs. Time
Figure 3. Nonrepetitive On−State Impulse vs.
Waveform (IPPS
(ITSM
)
)
Detailed Operating Description
The TSPD or Thyristor Surge Protection Device are
specialized silicon based overvoltage protectors, used to
protect sensitive electronic circuits from damaging
overvoltage transient surges caused by induced lightning
and powercross conditions.
The electrical characteristics of the TSPD help the user to
define the protection threshold for the circuit. During the
open circuit condition the device must remain transparent;
this is defined by the I
. The I
should be as low as
DRM
DRM
possible. The typical value is less than 5 mA.
The TSPD protects by switching to a low on state voltage
when the specified protection voltage is exceeded. This is
known as a “crowbar” effect. When an overvoltage occurs,
the crowbar device changes from a high−impedance to a
low−impedance state. This low−impedance state then offers
a path to ground, shunting unwanted surges away from the
sensitive circuits.
The circuit operating voltage and protection voltage must
be understood and considered during circuit design. The
V
(BO)
is the guaranteed maximum voltage that the protected
circuit will see, this is also known as the protection voltage.
The V is the guaranteed maximum voltage that will
DRM
keep the TSPD in its normal open circuit state. The TSPD
is typically a 20−30% higher than the V . Based
V
(BO)
DRM
This crowbar action defines the TSPD’s two states of
functionality: Open Circuit and Short Circuit.
Open Circuit – The TSPD must remain transparent during
normal circuit operation. The device looks like an open
across the two wire line.
on these characteristics it is critical to choose devices which
have a V higher than the normal circuit operating
DRM
voltage, and a V
which is less than the failure threshold
(BO)
of the protected equipment circuit. A low on−state voltage
V allows the TSPD to conduct large amounts of surge
t
Short Circuit – When a transient surge fault exceeds the
TSPD protection voltage threshold, the devices switches on,
and shorts the transient to ground, safely protecting the
circuit.
current (500 A) in a small package size.
Once a transient surge has passed and the operating
voltage and currents have dropped to their normal level the
TSPD changes back to its open circuit state.
I
(OP)
+
+
•TSPD looks like an open
•Circuit operates normally
Protected
V
−
TSPD
(OP)
Equipment
−
Normal Circuit Operation
•Fault voltage greater than V occurs
bo
I
(Fault)
•TSPD shorts fault to ground
•After short duration events the O/V
switches back to an open condition
•Worst case (Fail/Safe)
•O/V permanent short
•Equipment protected
+
+
I
Protected
(Fault)
V
TSPD
(Fault)
Equipment
−
−
Operation during a Fault
Figure 4. Normal and Fault Conditions
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