Datasheet LPSA 300 (Vishay) - 3

LPSA 300
www.vishay.com 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 Bluesil Past 340 from BlueStar Silicones) or a thermal film (type Q Pad II) easier and faster to install than the grease. • The fastening of the resistor to the heatsink is under pressure control of two screws tightened at 2 Nm for full power availability. LPSA 300
Tightening Torque on Heatsink
2 Nm • The following accessories are supplied with each product: - 2 screws CHC M4 x 25 class 8.8 and 2 M4 contact lock washers for heatsink mounting - 2 screws TH M4 x 6/6 and 2 M4 contact lock washers for connections. 2 off CHC M4 x 16/16 class 8
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 120 °C. The dissipated power is simply calculated by the following ratio: T P = ---------------------------------------------- R + R + R TH (j - c) TH (c - h) TH (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 specifications environmental paragraph). 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 LPSA 300 power dissipation 180 W at + 50 °C room temperature. T  120 °C - 50 °C = 70 °C T 70 RTH (j - c) + RTH (c - h) + RTH (h - a) = ---- = ------- = 0.388 °C/W P 180 RTH (j - c) = 0.112 °C/W RTH (c - h) + RTH (h - a) = 0.388 °C/W - 0.112 °C/W = 0.276 °C/W
OVERLOADS
In any case the applied voltage must be lower than UL = 5000 V.
Short time overload:
4 x Pr/10 s
Accidental overload:
The values indicated on the following graph are applicable to resistors in air or mounted onto a heatsink. Revision: 21-Nov-2019
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Document Number: 50076 For technical questions, contact: [email protected] 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