Datasheet

DTO25
www.vishay.com
Vishay Sfernice
Revision: 23-Oct-2019
3
Document Number: 51054
For technical questions, contact: [e-mail]
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
POWER RATING
The temperature of the case should be maintained within the limits specified.
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 150 °C. The dissipated power is simply calculated by the following ratio:
P: Expressed in W
T: Difference between maximum working temperature and room temperature
R
TH (j - c)
: Thermal resistance value measured between resistive layer and outer side of the resistor. It is the thermal resistance
of the component: 5 °C/W.
R
TH (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.
R
TH (h - a)
: Thermal resistance of the board.
Example:
R
TH (c - h)
+ R
TH (h - a)
for DTO25 power rating 3 W at ambient temperature +25 °C.
Thermal resistance R
TH (j - c)
: 5 °C/W
Considering equation
(1)
we have:
T = 150 °C - 25 °C = 125 °C
R
TH (j - c)
+ R
TH (c - h)
+ R
TH (h - a)
= T/P = 125/3 = 41.7 °C/W
R
TH (c - h)
+ R
TH (h - a)
= 41.7 °C/W - 5 °C/W = 36.7 °C/W
ACCIDENTAL OVERLOAD
In any case the applied voltage must be lower than the maximum overload voltage of U
s
= 750 V. The values indicated on the
graph below are applicable to resistors onto a board.
10
100
1000
10000
0
20
40
60
80
100
0 50 100 150 200
Axis Title
1st line
2nd line
2nd line
Rated Power (%)
Case Temperature (°C)
25
P
T
R
TH (j - c)
R
TH (c - h)
R
TH (h - a)
++
-------------------------------------------------------------------------------------------
1
=