MOSFET Based Solid State Relays (SSR)

This project describes an approach to using MOSFETs in SSRs and measures their performance.

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Commercial SSRs are expensive, bulky, and have high dissipation. MOSFETs can be used to achieve better performance and lower dissipation at lower costs and, can integrate better into a system design. This project examines the use of an isolated flyback to drive them.

Schematic & PCB in Eagle for DPST reference design.

Zip Archive - 52.86 kB - 03/28/2018 at 13:41


Firmware for DPST reference design. Written in XC8 for the 12F1612 Microchip controller using MPLab.

Zip Archive - 7.89 kB - 03/28/2018 at 13:41



This document describes the work in detail.

Adobe Portable Document Format - 1.20 MB - 03/28/2018 at 13:32


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Brian Cornell wrote 03/28/2018 at 16:49 point

Hi K.C., good points on the creepage & clearance.  I chose to stay away from that area due to the complexity of the requirements and rather focus on the concept.  That said, yes the design would require modifications to meet. 

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K.C. Lee wrote 03/28/2018 at 14:55 point

Dual Photovoltaic MOSFET Driver Solid-State Relay
SSR Design Using VO1263 - Vishay

It uses Photovoltaic cells to drive external MOSFET.  Much better in size, isolation and lower power.  

To get the rated isolation, you have to understand the creepage rules for PCB.  Most common mistake is routing tracks in between the primary/secondary side of optoisolators!


Watch out for the freewheeling diode inside the MOSFET.  Your SSR is only good for DC.  You'll need back to back MOSFET in series for AC SSR.

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