Dto25, Vishay sfernice – C&H Technology DTO25 User Manual
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For technical questions, contact: [email protected]
Document Number: 51054
16
Revision: 19-Jan-09
DTO25
Vishay Sfernice
Surface Mounted Power Resistor
Thick Film Technology
Preliminary
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 exceed 150 °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: 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.
R
TH (c - 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:
ΔT = 150 °C - 25 °C = 125 °C
R
TH (j - c)
+ R
TH (c - a)
=
ΔT/P = 125/3 = 41.7 °C/W
R
TH (c - 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 Us = 375 V. The values indicated on the
graph below are applicable to resistors 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)
[
]
+
---------------------------------------------------------------
=
0.01
0.1
1
10
100
10
-7
OVERLOAD DURATION IN s
ENERGY IN J
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
ENERGY CURVE
E
P x t
U
2
R
------- x
t
=
=