Solid State Relays
How Do Solid State Relays Work?
Solid state relays (SSR) for PCB mounting are partially pin-compatible with electromagnetic relays. Therefore, they can often serve as no-fuss replacements in existing designs, so that users can quickly benefit from the advantages offered by solid state relays. SSRs are not actually relays in the conventional sense, even though they are generally categorized as such. Instead, SSRs are electronic components made with transistors or thyristors. Because they operate without moving parts, solid state relays offer a long operating life. In addition, they are suitable for high switching cycles and adverse environments. Solid state relays are capable of switching AC voltages at the zero crossing point, thus making it possible to avoid interference pulses. They also support the integration of optocouplers on the IC to achieve galvanic separation.
Compared to mechanical relays, SSRs have higher losses in the load current path and therefore often have to be mounted on a heat sink.
Samples ContactsSolid State Relays vs PhotoMOS Relays
So-called PhotoMOS relays are special solid state relays variants which are constructed similarly to an optocoupler. On the control side, these relays operate like an optocoupler with an IR LED. At the same time, on the load side they are not equipped with thyristors like conventional SSRs, but with MOSFETs. This makes it possible to switch on and off an AC circuit connected between the two drain terminals or two DC circuits, one of which is connected between the source terminal and the two drain terminals.
PhotoMOS relays do not require cooling and have a lower voltage drop at low load currents than other types of solid state relays. However, they typically have a higher contact resistance than mechanical relays. PhotoMOS relays also operate reliable, without bounce and at high switching speeds, while special versions are able to reach switching frequencies of up to 100kHz.
Manufacturers & Contacts
CELDUC
CELDUC is a leading specialized manufacturer of semiconductor relays and magnetic sensors. The basic product range comprises 1- to 3-phase solid state relays, motor reversal protection modules and motor soft-start modules.
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GOODSKY
GOODSKY Electric is a leading manufacturer of electromechanical relays for applications in white and brown goods, industry, telecommunications, and office automation, as well as in the automotive industry.
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