D2TO20

www.vishay.com

Vishay Sfernice

Revision: 17-Mar-16

3

Document Number: 51055

For technical questions, contact: sferfixedresistors@vishay.com

THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT

ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000

CHOICE 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 exceed 175 °C. The dissipated power is simply calculated by the following ratio:

P:

Expressed in W

T:

Difference between maximum working temperature and room temperature or fluid cooling temperature

RTH (j - c): Thermal resistance value measured between resistive layer and outer side of the resistor. It is the thermal resistance

of the component: 6.5 °C/W.

RTH (c - h): Thermal resistance value measured between outer side of the resistor and upper side of the board. This is the thermal

resistance of the solder layer.

RTH (h - a): Thermal resistance of the board.

Example:

RTH (c - h) + RTH (h - a) for D2TO20 power rating 2.5 W at ambient temperature +25 °C.

Thermal resistance RTH (j - c): 6.5 °C/W

Considering equation (1) we have:



T = 155 °C - 25 °C = 130 °C

RTH (j - c) + RTH (c - h) + RTH (h - a) = T/P = 130/2.5 = 52 °C/W

RTH (c - h) + RTH (h - a) = 52 °C/W - 6.5 °C/W = 45.5 °C/W

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 (W): Resistor

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

P

T

R

TH (j - c)

R

TH (c - h)

R

TH (h - a)

++

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

1



=

E

P x t

U

2

R

--------

x t

==