Wire selection and PCB Layout to reduce Inductive Noise


#1

Solid State Relays only require a small amount of power to operate, so even a little inductive noise is enough to result in a system malfunction. To avoid inductive noise, it is important to be aware of proper wire selection and trace routing in your circuit board layout.

  1. Wire Selection
    Please do not connect power lines next to input lines because this easily causes inductive noise to affect the solid state relay. If inductive noise is imposed on the input terminals of the solid state relay, the following cables can help.
  • Twisted-pair cable: to reduce electromagnetic noise

  • Shielded cable: to reduce static noise

  1. Circuit Board Layout
    Before routing the circuit board layout, please check the SSR’s specification to determine what creepage distance and clearance distance are suggested. For example, Toshiba, TLP175A has the below design requirements listed in its datasheet.
    mechanical

Remarks:

  • Creepage distance is the shortest path between two conductors (or between a conductor and the bounding surface of the equipment) measured along an insulation surface.
  • Clearance distance is the shortest distance between two conductors (or between a conductor and the bounding surface of the equipment) measured through the air.
  1. Other
    Consider using a filter which consists of a combination of capacitor and resistor; this will effectively reduce noise generated from high-frequency equipment too.
    filter

#2

LC filter is better than RC filter , I think.


#3

Yes, an RC filter will dissipate more power and display worse noise rejection than an LC filter.
But RC filters are less costly than LC filters. RC filters are also inherently free of resonance, while an LC filter may resonate if not properly damped.


#4

It is hard to say which RC filter or LC filter will dissipate more power, it depend on real application.