Solid-State Relays

A solid-state relay (SSR) is constructed using a photo-sensitive metal-

oxide semiconductor field-effect transistor (MOSFET) that is controlled

using a light emitting diode (LED). Light from the encapsulated LED

actuates the photo-sensitive MOSFET and allows current to flow through

it. LED actuation provides a galvanic isolation barrier (no charge can

flow) between the control circuitry and the MOSFET. This is analogous to

the isolation barrier formed between the magnetic coil and the

mechanical armature in electromechanical relays.

There are two main advantages to using SSR technology in PXI:

extended lifetime and unlimited simultaneous crosspoint connections.

Because SSRs use solid-state devices (MOSFETS) to switch states

instead of mechanical contacts, they have infinite mechanical lifetime.

PXI switch modules that are based on SSR technology last longer and

help reduce overhead in many applications by eliminating the need for

frequent switching component replacement.

Compared to electromechanical relays, SSRs require very little power to

transition between ON and OFF states.This feature is especially useful

when building PXI switch systems. The PXI backplane supplies limited

power to each slot in the chassis. Most high-density electromechanical

relay-based matrix modules require more power than that available from

the backplane to close all crosspoints simultaneously. SSR-based matrix

modules are not limited in the same way due to the low power consumption

of SSR technology.

The PXI-2533 and PXI-2534 256-crosspoint matrix modules are

high-density switch products that incorporate SSR technology. Both

modules offer unlimited mechanical lifetime and unlimited

simultaneous crosspoint connections while providing the ability to

switch up to 55 V at 1 A on all channels.

Topology Diagrams

256-Crosspoint SSR Matrix Modules

BUY ONLINE at ni.com or CALL 800 813 3693 (U.S.)

LED

MOSFET

Control

Circuitry

Mixed Case Isolation Barrier

High Voltage

Load

Figure 1. Solid-State Relay Construction

R0

C0

C1

C2

C3

C63

R1

R2

R3

R2

Diagram 1. PXI-2533 4x64 1-Wire

R6

R0

R1

R6

R7

C0

C1

C2

C3

C31

Diagram 2. PXI-2534 8x32 1-Wire