STK795 Sanyo, STK795 Datasheet - Page 4

• Manufacturer Part Number: STK795
• Description: Chopper Type Voltage Regulator
• Manufacturer: Sanyo

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Thermal Design
The total internal power dissipation in the IC is related to the output current as shown below. Assuming V
output current=3A, the total internal power dissipation is 2.7W.
Assuming that the IC case temperature (Al plate) is 85 C (Tc max=105 C) and the temperature inside equipment is 60 C
max., the thermal resistance required of the heat sink is as shown below.
For 2mm thick Al plate (black coated), the area is 30cm
Junction temperature Tj of the power transistor which forms a main heat source is calculated as follows :
Since the actual thermal resistance of the heat sink greatly depends on various conditions such as the layout of equip-
ment or ventilation, allow an ample margin in thermal design.
c-a=
The thermal resistance of the power transistor is : j-c=6.2 C/W
Therefore, Tj is calculated using
=9.3 C/W
85 C–60 C
2.7W
Tj=Pd
Tj=2.7W 6.2 C/W+85 C=101.7 C
j-c+Tc.
STK795
2
. (55 55 2t)
in(DC)
No.1709–4/5
=12V,