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RTOP

Power Resistors for Mounting Onto a Heatsink Thick Film Technology

Vishay Semiconductors 

www.vishay.com

RTOP

Vishay Sfernice

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 heatsink must be around 6.3 μm. In order to improve thermal conductivity, surfaces in contact (alumina,

heatsink) should be coated with a silicone grease (type SI 340 from Rhône-Poulenc or Dow 340 from Dow Corning)

Tightening Torque on Heatsink

RTOP

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

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 = -R----T---H------(-j-------c---)---+-----R-----T---H------(-Tc---------h---)---+-----R----T---H------(-h---------a---)

P:

Expressed in W

T:

Difference between maximum working temperature and room 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 (see table Special Features)

RTH (c - h): Thermal resistance value measured between outer side of the resistor and upper side of the heatsink

This is the thermal resistance of the interface (grease, thermal pad), and the quality of the fastening device

RTH (h - a): Thermal resistance of the heatsink

Example:

RTH (c - a): For RTOP 200 power rating 130 W at ambient temperature +30 °C.

Thermal resistance (see table 1) RTH (j - c): 0.5 °C/W

T = 125 °C - 30 °C  95 °C 

RTH (j - c) + RTH (c - h) + RTH (h - a) = --P---T- = 1--9-3--5-0-- = 0.73 °C/W

RTH (j - c) = 0.112 °C/W

RTH (c - h) + RTH (h - a) = 0.73 °C/W - 0.5 °C/W  0.23 °C/W

Revision: 06-Apr-18

3

Document Number: 50045

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

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