July 13, 2009

Sanken launches SZ-10M20C bypass diode for solar cells
~ Realizes ultra-low thermal resistance and improved heat dissipation ~

Sanken Electric Co., Ltd. announces the development of SZ-10M20C bypass diode for solar cells. The SZ-10M20C features withstand voltage of 1,000 V and 20 A current. Sanken provides the SZ-10M20C in an original SZ-10 package enabling 1/8th the thermal resistance of conventional products housed in TO220F package. Samples of the SZ-10M20C are available now, at a unit price of 250 yen. Mass production is scheduled to begin in October this year at an initial scale of 30,000 units per month, to be ramped up to 500,000 units per month by 2011.
1. Development Background and Product Overview
  Solar power generation systems emit less CO2 when generating electricity. The market for these systems is therefore growing among today's environmentally conscious consumers.

Solar power generation systems consist of a solar panel on which multiple solar cells are connected in series. One problem with solar panels is that if any section of the solar panel is shaded by a building, tree, or power line, the power output of the solar cells on that section drops, and those cells operate as resistors. This lowers the generating efficiency of the panel as a whole. However, this problem can be prevented by inserting bypass diodes to reroute the current around the low-output cells.

Improving conversion efficiency of the solar cells tends to increase the output current. This also increases the current flowing through the bypass diodes, causing them to generate a lot of heat. It is therefore necessary to both lower the amount of heat generated and improve the dissipation of generated heat by attaching a heat sink.

The heat generation increases in proportion to the forward voltage (VF). Sanken's new bypass diode, the SZ-10M20C, reduces VF by about 10% (up to 0.97 V) compared to previous TO220F-package bypass diodes. This enables a significant reduction in the amount of heat generation.

Also, by adopting an original package with low thermal resistance (the SZ-10 package), Sanken has succeeded in cutting the diode's thermal resistance to 0.5°C/W. This is a mere 1/8th of the thermal resistance of conventional bypass diodes. The new package is also structured to facilitate the transfer of heat from the chip to the frame. Moreover, because the frame is attached directly to a heat sink, heat is easily transferred to the heat sink, realizing improved heat dissipation compared to TO220F package, which uses a resin frame.
2. Features
(1) Improved heat dissipation
The SZ-10M20C comes in an original package in which the frame is attached directly to a heat sink (package dimensions: 10 x 14 x 5 mm). This reduces thermal resistance to 1/8th (0.5°C/W max.) as compared to conventional TO220F-package products.
(2) Low power dissipation (VF = 0.97 V max.)
VF is about 10% lower than conventional bypass diodes, reducing the power dissipation.
(3) High resistance to heat (Tj = 190°C)
The heat resistance is high, facilitating heat-dissipation design.
(4) High withstand voltage (VR = 1,000 V)
The withstand voltage is considerably higher than the total output voltage of solar power generation systems (400 to 500 V), and is high enough to protect against lightening-induced surge.
3.  Specifications
Parameter Symbol Rating Unit
Reverse voltage VR 1000 V
Forward current IF(AV) 20 A
Forward voltage VF 0.97 max V
Junction temperature Tj -40 to +190 °C
Thermal resistance Rth(j-c) 0.5 max °C/W
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