Surge protection?

[cbiblis]

Can someone tell me if a circuit ran from a 120v transformer needs surge protection. It has a 1000uf cap full bridge rectifier, and voltage regulators. I have a thermostat design and i was wondering if i should incorporate a surge protector into the design. The thermo is designed for incubators and will most likely be wired in someones barn or shed that is most likely improperly wired. The circuit doesn't have a ground as of now. Thanks for any suggestions.

 

[MikeMl]

A "transzorb" line-to-neutral across the input to the transformer is a good idea. You should be fusing the line, so put the transzorb across the primary of the transformer. The transformer itself is a pretty-good transient filter from primary to secondary, as is the filter capacitor on the secondary.

 

[cbiblis]

A "transzorb" line-to-neutral across the input to the transformer is a good idea. You should be fusing the line, so put the transzorb across the primary of the transformer. The transformer itself is a pretty-good transient filter from primary to secondary, as is the filter capacitor on the secondary.

Which transzorb do you suggest i use for the 120v/12v@100ma Transformer? I looked at digikey and they had thousands of them.

 

[MikeMl]

Here you go: Mouser in stock

 

[westom]

Can someone tell me if a circuit ran from a 120v transformer needs surge protection.

Electronics should be designed to withstand transients of up to 600 volts - both longitudinal and normal modes. Between a transformer, rectifier diodes, filtering, etc, making normal mode transients irrelevant is easy. Destructive transients use electronics to obtain earth ground. That is the protection that a transzorb at electronics will not solve.

So that protection designed inside all electronics is not overwhelmed, protection is best located where transients may enter the building. Either that energy harmlessly dissipates in earth. Or is inside the building hunting for earth destructively via electronics. Any transients inside the building would be made irrelevant by your electronics design. Transients that can overwhelm that protection must be earthed as the service entrance. Which is why high reliability facilities (ie telco COs) locate protectors as close to earth as possible and up to 50 meters distant from electronics. That separation makes protection even more effective.