A Robust Protection Scheme
The circuit diagram in Figure 1 shows a robust protection
scheme for these applications. The solution is based on a
"Stacked" GDT, a series Inductor, and a Power TVS diode
or other clamping devices with similar performance. The
components are selected based on their ability to handle a
specific range of 8/20µS and 10/350µS surges.
A Stacked GDT is a single component that consists of a
number of GDTs in series. This is represented by the symbol
in the schematic in Figure 2. The arrangement of capacitors
C1 through C4 ensures the impulse sparkover voltage for
the stack is only slightly higher than for a single GDT. The
Recommendation ITU-T K.99 provides a description of the
operation of GDTs in series. The inductor is an air-core inductor
with low permeability to support a large surge current flow
without saturation. During a large surge, the inductor is the
coordinating element between the secondary overvoltage
protection (e.g. Power TVS diode) and the Stacked GDT.
| 13 |
Document Title Notes
GR-1089-CORE Electromagnetic Compatibility (EMC) and
Electrical Safety―Generic Criteria for
Network Telecommunications Equipment
Issue 7, December 2017,
Port Type 8a
IEC 61000-4-5 Electromagnetic compatibility (EMC) ―Testing and
measurement techniques―Surge immunity test
Edition 3.0
IEC 60950 Information technology equipment―Safety
ETSI 300-132-2 Equipment Engineering (EE);
Power supply interface at the input to
telecommunications equipment;
Part 2: Operated by direct current (DC)
Figure 1: Protection Scheme Circuit Diagram (Source: Bourns, Inc.)
Table 1: Related Standards
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HIGH-SPEED PROTECTOR
PRODUCTS
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• Transient protection for very high data
rate differential lines
• Provide an extremely low let-through
energy barrier against excessive
voltages
• Enable low voltage electronics
to be protected by a lower capacitance,
higher voltage TVS device
• Protect sensitive equipment from damage
caused by lightning and electrical
transient surges
• Integrate circuit protection devices into
an assembly that provides an enhanced
level of protection
• SPD product line includes protective
devices for AC systems, DC power
systems, signal and data line circuits
SURGE PROTECTIVE DEVICES (SPD)
