D2to20, Vishay sfernice – C&H Technology D2TO20 User Manual
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Document Number: 51055
38
Revision: 24-Nov-08
D2TO20
Vishay Sfernice
Surface Mounted Power Resistor
Thick Film Technology
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
ΔT:
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: 6.5 °C/W.
R
TH (c - a )
:
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:
R
TH (c - a)
for D2TO20 power rating 2.5 W at ambient temperature + 25 °C.
Thermal resistance R
TH (j - c)
: 6.5 °C/W
Considering equation (1) we have:
ΔT = 155 °C - 25 °C = 130 °C
R
TH (j - c)
+ R
TH (c - a)
=
ΔT/P = 130/2.5 = 52 °C/W
R
TH (c - a)
= 52 °C/W - 6.5 °C/W = 45.5 °C/W
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 (
Ω): Resistor
The energy calculated must be less than that allowed by the graph.
P
ΔT
R
TH (j - c)
[
]
R
TH (c - a)
[
]
+
---------------------------------------------------------------
=
10
-6
10
-5
10
-4
10
-3
10
-2
ENERGY IN JOULES
OVERLOAD DURATION IN s
ENER GY CURVE
0.01
0.1
1
10
E
P x t
U
2
R
------- x
t
=
=