C&H Technology RTOP - Manual (Page 4)

www.vishay.com For technical questions, contact: [email protected] Document Number: 50045
3 Revision: 14-Nov-08
RTOP
Vishay Sfernice Power Resistor for Mounting onto a Heatsink
Thick Film Technology
CHOICE OF THE HEATSINK
The user must choose the heatsink according to the working
conditions of the component (power, room temperature).
Maximum working temperature must not exceed 125 °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 (see
Table Special Features).
R
TH (c - a)
: Thermal resistance value measured between
outer side of the resistor and room temperature.
It is
the thermal resistance of the heatsink
depending on the heatsink itself (type, shape)
and the quality of the fastening device.
Example:
R
TH (c - a)
: For RTOP 200 power rating 130 W at ambient
temperature + 30 °C.
Thermal resistance (see table 1) R
TH (j - c)
: 0.5 °C/W
OVERLOADS
The applied power is 2.5 x rated power for 5 s with a max.
voltage of 2 x nominal voltage.
Accidental overload: The values indicated in the graph
below are applicable to resistors in air or mounted onto a
heatsink.
In case of multi-resistor devices, (DRTOP, TROP and
QROP) the results apply to each resistor value in the device.
RECOMMENDATIONS FOR MOUNTING
ONTO A HEATSINK
Surfaces in contact must be carefully cleaned.
The heatsink must have an acceptable flatness:
from 0.05 mm to 0.1 mm/100 mm.
Roughness of the heater must be around 6.3 µm.
In order to improve thermal conductivity, surfaces in contact
(alumina, heatsink) are laid on with a silicone grease (type SI
340 from Rhône-Poulenc or Dow 340 from Dow Corning).
Tightening torque on heater: 2 Nm
For the electrical connections, it is recommended to use
M4 x 6 screws and if necessary a washer of 1mm thickness.
The recommended screw tightening torque is 1 Nm.
P
ΔT
R
TH j c – ( ) R
TH c a – ( ) +
[ ]
------------------------------------------------------------- 1 ( )
=
ΔT 125 °C - 30 °C - 95 °C ≤ ≤
R
TH (j - c)
R
TH (c - a)
ΔT
P
-------
95
130
---------- 0.73 °C/W = = = +
R
TH (j - c)
0.5 °C/W
≤
R
TH (c - a)
0.73 °C/W - 0.5 °C/W 0.23 °C/W
≤ ≤
ENERGY CURVE
OVERLOAD DURATION IN SECONDS
ENERGY IN JOULES
1.10 -7 1.10 -6 1.10 -5 1.10 -4 1.10 -3 1.10 -2 1.10 -1 1
RTOP DRTOP
0.01
0.1
1
10
100
1000