Re: Low-voltage relay help


Yes there are solutions. You may not want to use a magnetically latched signal as it may require another signal to release.

Some ideas you can consider.

The voltage level with which you are dealing is TTL. If you do a web seach on “TTL driven Relay” it will bring up a number of possibilities. One possibility is the Tecnec TCR102  ( It requires an external power supply but this can come from your PLC I/O supply (there are a number of voltage options available) . The load on the driving signal is only uA at the TTL 5V level so should suit your application. This is an industial type unit which you can wire straight in.

Another possibility is to use a reed reed relay. You can get low power coils in these but they are generally designed for printed circuit board applications so are small and fiddly. You would need to devise a mounting and connecting method. Try a websearch on “reed relay” and check out the range that Farnell has.  

The lowest cost and crudest solution would be to select a suitable transistor, drive the base with your 5V signal and use the collector, powered by the PLC 24V supply, to switch a relay coil. Depending on the configuration of yout PLC input module you may even be able to rig to switch it directly (without the relay). May require a bit of mucking around. A disadvantage of this is that it would common the OV rails of your TTL level signal and the PLC and you may not want to do this.