FIG. 1 is a simplified cross-sectional view of a prior art junction box for a solar panel that utilizes photovoltaic (PV) cells to convert solar energy into electric power. The junction box 10 includes a plastic box 12 having a base portion 14 for mounting the box to a solar panel 16. A plastic cover 18 engages the box to seal off the inside of the box from moisture, dust and other contaminants. A printed circuit board 20 includes circuitry for making connections between conductive leads from the panel and cables that carry power to a power distribution system. The conductive leads and cables are omitted from FIG. 1 to avoid obscuring the remaining structure of the junction box.
The printed circuit board 20 also includes one or more bypass diodes 22 which are used to prevent damage to the solar panel or other components and improve efficiency under certain operating conditions. The diode 22 shown in FIG. 1 has a plastic package body 24 and a metallic slug 26 which acts as a heat sink to dissipate heat generated within the diode body. The diode 22 is electrically connected to the printed circuit board 20 through wire leads 28.
To prevent damage to the diode if it overheats, the plastic body of the diode is positioned in physical contact with a thermally conductive plate 30 which is bonded to the cover 18. The thermally conductive plate 30 is fabricated from a metal such as copper or aluminum and acts as a heat spreader to distribute heat from the diode across a relatively large surface area of the cover, thereby enabling heat from the diode to be dissipated through the cover of the junction box.
The diode is designed to dissipate heat primarily through the metallic slug which forms a thermal interface with the printed circuit board. Since the printed circuit board only has a limited capacity to dissipate heat, the conductive plate enables some additional heat to be dissipated through the plastic body of the diode, which has relatively low thermal conductivity. Thus, the prior art arrangement of FIG. 1 fails to fully utilize the primary heat dissipating mechanism of the diode, and it provides poor thermal management.