Application Note

VISHAY DRALOR IC
Resistive Products
Application Note
Z302 Axial Cemented Wirewound Safety Resistor
FEATURES
• All welded construction
Alloy resistance wire, wound to
specific parameters on high
thermal conductivity ceramic core
• Ceramic core
• P40 = 3 W
• Ohmic range 10R to 100R, 5 %
Flame retardant
thermocoat
All welded cap
and lead assembly
• Special cement coating for immediate interruption without
flame and explosion when mains voltage (220 VRMS) is
applied
• Lead (Pb)-free and RoHS compliant
Vishay has introduced special version of Z302 wirewound resistors to be used as safety resistor (or, AC mains input resistors).
It uses specially selected resistive winding wire and special coating material to ensure safe and silent fusing operation in
overload conditions. The resistor fuses “without a bang” when AC mains voltage is applied. At the same time, it acts as a in-rush
current limiting resistor for the normal operation. The specially developed lacquer coating matches the thermal and electrical
insulating properties of standard silicone cement. This allows designers to more easily meet the requirements of UL approval,
whilst eliminating the need to put additional fuses in series with the input resistor.
In the conventional wirewound resistor, ceramic rod at the resistor's core acts as a heat sink for the wire element. This can delay
fusing, resulting in high enough temperatures to fragment the coating and ionize the air near to where fusing occurs. If ionization
occurs close to the cap edge and at a voltage peak in the mains cycle, it can initiate a momentary flashover outside the
component body, releasing far more energy than is required to fuse the wire element. Although the opening of the circuit is safe
for most applications, it can be with a “bang” with splattering of cement coating. This is un-safe operation and not desirable.
New coating material and process gives silent and safe fusing performance to Z302 safety resistors. The new multi-layer coating
has a flammability rating conforming to UL 94 V-0 and shares the same high temperature and insulating properties as standard
silicone cement. However, it can absorb thermal and mechanical stresses without fragmenting. The resistor coating does not
burn or emit incandescent particles under any condition of applied temperature or power overload.
KEY SPECIFICATIONS
• Surge voltage capability: 1.8 kV (30 pulses/15 min) as per IEC 61000-4-5
• Fusing time < 30 s for 45 W overload
• Fusing time < 2 s when connected across the mains 90 VAC to 264 VAC/50 Hz to 60 Hz without flames, explosion or smoke.
Resistance value after fusing > 100 kΩ
Document Number: 21030
Revision: 17-Mar-10
For technical questions, contact: [email protected]
www.vishay.com
1
APPLICATION NOTE
These resistors are available in standard values of 10R, 20R with 5 % tolerance. Other ohmic values are also available on
customer request from 10 Ω to 100 Ω. The devices are designed to withstand inrush and surge conditions.
Application Note
Vishay Draloric
Z302 Axial Cemented Wirewound Safety Resistor
PHYSICAL CONFIGURATION
G
B
A
C
SPECIFICATIONS
MODEL
RATED
DISSIPATION
P40 °C
TOL.
±%
“A”
MAX.
(mm)
“B”
MAX.
(mm)
“C”
(mm)
“G”
(mm)
MARKING
Z320414
3W
5
13.0
5.5
0.8
53 ± 1
SR
PACKAGING
500 pieces ammo pack.
ORDERING INFORMATION
Example: To order a 20 Ω, 3 W, safety resistor, the part number will be: Z32041432009J2CCS0.
The first 15 digits are as per ordering information given in the Z300 datasheet. Last 3 special digits “CSO” specifies safety
resistor. (www.vishay.com/doc?21007)
APPLICATION NOTE
For further information, please contact: [email protected]
www.vishay.com
2
For technical questions, contact: [email protected]
Document Number: 21030
Revision: 17-Mar-10
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