electronic switch design

[goshantry]

The picture he posted earlier showed the correct voltages at the base and collector of the transistor. However the relay doesn't operate. I suspect he may be using the wrong relay, e.g. one with a 24V coil.

i tried with all the spdt relays available in the orcad library but still getting the same results with it

 

[D.A.(Tony)Stewart]

• Neutral is always connected to ground at the source, even a portable generator, the chassis ground will also be neutral even if floating. So by convention Neutral is grounded at source but load currents commonly raise that voltage a couple volts at the load if running at rated current.
  
• Relays are constructed differently depending on ratings and applications;
• review some datasheets here
  
  for example of types....
  
• Signal, Up to 2 Amps (4,403 items) = Gold plated to prevent corrosion eg for telephony signals
  
• Power, Over 2 Amps (9,643 items) = Need current arc to clean contacts from oxide buildup (insulator)
  
• Solid State (6,226 items) = optically coupled SSR for AC or transistor for DC
  
• SS relays often defined in 4 basic types if design specifically for Input or Output AC or DC so they are called IAC,IDC,OAC,OAC types.
  
• There are RF relays which use 50Ω lines and RF diodes with controlled impedances and DC isolation.
  
• If relays are very high current, they are called "contactors" instead and have arc suppression medium.
  
• Relays like transistors have a gain factor where the switch current rating / input current rating could be 100 typically.
  
• Relays have lots of bounce, bigger = longer time
  
• Optical switches often use hysteris to reduce noise effects
  
• Optical switches can also include zero crossing circuits

This is just relay 101 intro and my 2 pesos worth.
and that concludes this lecture.