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Document Number: 51058

24

Revision: 19-Jul-11

D2TO35

Vishay Sfernice

Surface Mounted Power Resistor

Thick Film Technology

This document is subject to change without notice.

CHOISE OF THE BOARD

The user must choose the board according to the working conditions of the component (power, room temperature). Maximum

working temperature must not exeed 155 °C. The dissipated power is simply calculated by the following ratio:

P:

Expressed in W

T:

Difference between maximum working temperature and room temperature

Thermal resistance value measured between resistive layer and outer side of the resistor. It is the thermal

resistance of the component: 4.28 °C/W.

Thermal resistance value measured between outer side of the resistor and room temperature. It is the thermal

resistance of the solder layer (according the quality of the soldering) and the thermal resistance of the board.

Example:

Considering equation (1) we have:

T = 175 °C - 25 °C = 150 °C

ACCIDENTAL OVERLOAD

In any case the applied voltage must be lower than the maximum overload voltage of 375 V. The values indicated on the graph

below are applicable to resistors in air or mounted onto a board.

Single Pulse:

These informations are for a single pulse on a cold resistor at 25 °C (not already used for a dissipation) and for pulses of 100 ms

maximum duration.

The formula used to calculate E is:

with:

E (J):

Pulse energy

P (W): Pulse power

t (s):

Pulse duration

U (V): Pulse voltage

R (

): Resistor

The energy calculated must be less than that allowed by the graph.

P

T

R

TH (j - c)



R

TH (c - a)



+

---------------------------------------------------------------

1



=

10

-6

10

-5

10

-4

10

-3

10

-2

OVERLOAD DURATION IN s

ENERGY CURVE

0.01

0.1

1

10

10

-7

10

-1

100

EP x t

U

2

R

------- x t

==