NP−SBMC Series

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5

TIME (ms)

0

50

0

100

Peak

Value

Half Value

1

10

100

0.1

1

10

100

1000

Figure 2. Nonrepetitive On−State Current vs. Time

Figure 3. Nonrepetitive On−State Impulse vs.

CURRENT DURATION (s)

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 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.

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.

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.

Figure 4. Normal and Fault Conditions

Protected

Equipment

+

−

+

−

TSPD

Normal Circuit Operation

Protected

Equipment

+

−

+

−

TSPD

Operation during a Fault

•TSPD looks like an open

•Circuit operates normally

•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

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;

possible. The typical value is less than 5

mA.

The circuit operating voltage and protection voltage must

be understood and considered during circuit design. The

circuit will see, this is also known as the protection voltage.

keep the TSPD in its normal open circuit state. The TSPD

on these characteristics it is critical to choose devices which

of the protected equipment circuit. A low on−state voltage

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.