Renesas PS7901D-1A optical-coupled MOSFET

Renesas has developed an optical-coupled MOSFET, the PS7901D-1A, that is claimed to achieve electrical isolation within the package by using light for signal transmission.

The device is 40% smaller than the PS78 series, while retaining a guaranteed isolation voltage of 500 rms. The MOSFET combines low output capacitance and low leakage current making it suitable for high-frequency signal control in applications such as IC testers.

An optical-coupled MOSFET device combines in a single package three different elements: on the input side a light-emitting diode that converts an electrical signal into light, and on the output side a photo voltaic 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 isolated from each other electrically. This type of device is also referred to as a solid state relay. In contrast to mechanical relays, semiconductor relays are not subject to malfunction due to worn contacts or contamination by foreign matter.

It has a low output capacitance of 0.75 pF and the MOSFET, as an output element, uses silicon-on-insulator technology enabling an output capacitance of 0.75 pF.

The output capacitance is about 25% lower than the 1 pF of the company’s existing compact-package products. This makes it possible to suppress signal component leakage and makes the device suitable for high-frequency operation.

Through optimisation of the gate film structure of the MOSFET, leakage current is reduced by 70%, from 100 to 30 pA. This contributes to equipment with high measuring precision.