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Optical-coupled MOSFET serves as solid-state relay

Posted: 07 Feb 2011     Print Version  Bookmark and Share

Keywords:optical-coupled MOSFET  solid state relay  signal transmission 

Renesas Electronics Corp. debuts the PS7901D-1A, an optical-coupled MOSFET that uses light for signal transmission to achieve complete electrical isolation within the package.

The device comes as an ultracompact 4-pin flat-lead package measuring 2.9 × 2.3mm, which is 40 per cent smaller than that of Renesas Electronics' existing PS78 Series products. It offers guaranteed isolation voltage of 500Vrms, equivalent to the company's existing products.

The MOSFET chip inside the package combines low output capacitance and low leakage current. The extremely low leakage current when in the off state makes the PS7901D-1A suitable for high-frequency signal control in applications such as IC testers.

The device combines an LED that converts an electrical signal into light, a photovoltaic diode that converts light into an electrical signal, and an output MOSFET. The use of light to transmit the signal means that the input and output sides are completely isolated from each other electrically. This type of device is also referred to as a solid state relay (SSR). In contrast to mechanical relays, semiconductor relays are not subject to malfunction due to worn contacts or contamination by foreign matter. For this reason, mechanical relays are being replaced SSR in a wide range of applications, including IC testers, factory automation equipments, electric household appliances, and communication equipments.

Demand has grown in the measuring equipment market for SSR that are more compact and capable of operation at higher speeds as the trend in the devices being tested moves towards higher speed, better performance, and higher pin counts as part of a general tendency towards improved performance and processing power. Especially the IC testers incorporate a large number of switches for signal switching, and there is demand for compact and high-speed optical-coupled MOSFETs for use in such products to achieve reduced equipment size and better performance. Nevertheless, reducing the package size of optical-coupled MOSFETs involves solving the extremely difficult challenge of both maintaining sufficient isolation distance to ensure adequate isolation voltage and achieving high optical coupling efficiency.

The PS7901D-1A device satisfies the above requirements and contributes to the development of equipment that combines compact size and performance.

Key features of the PS7901D-1A device are its compact package with approximately 40 per cent reduced mounting area; low output capacitance of 0.75pF; and 70 per cent lower leakage current than the company's existing Renesas, to 30pA.

The company says the product is suitable for a wide range of applications where compactness and thin form factor are desirable, including measuring equipment such as IC testers, factory automation equipment, and office equipment.

Samples of the PS7901D-1A device are available now and are priced at Rs.114.67 ($2.50). Mass production is scheduled to begin in the first half of FY2011 and is expected to reach a production volume of 10,00,000 units per month.

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