• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

OVER/UNDRE Current AND Short Protection Circuit

Status
Not open for further replies.

ASIF HUSSAIN

New Member
I want to design an over load and short protection circuit for home use
and without connecting it directly to the home appliances (i.e ) Transformer coupled ,is it possible by using any op amp.
If any one of u can provide me such a circuit,i,ll be very thank full .
 

tcmtech

Banned
Most Helpful Member
Use a current transformer and couple that with a voltage sensing circuit and you could possibly make a over/under voltage and current monitor.
 

Sceadwian

Banned
Circuit breakers are okay for over current but not for short circuit protection, at least not to protect digital electronics, motors and static loads maybe, the instantaneous current flowing from a dead short will fry digital electronics LONG before the breaker trips. After reading "The Art of Electroncs" it says the most common simple method of short circuit protection is a zener diode feeding the gate of an SCR. The SCR is set as a crowbar which will blow a fuse rather than let the current through to the circuit.
 

MikeMl

Well-Known Member
Most Helpful Member
... After reading "The Art of Electroncs" it says the most common simple method of short circuit protection is a zener diode feeding the gate of an SCR. The SCR is set as a crowbar which will blow a fuse rather than let the current through to the circuit.

What you describe is a "Crowbar" over-voltage protection circuit; not over-current protection. The purpose of a crowbar is to blow the fuse quickly to remove the over-voltage from the protected device. It would not even fire the SCR if a short circuit occured.

You could design a current crowbar. The gate of the shunt SCR would have to be triggered by excessive load current. Much more common is a current-limiter, which automatically reduces the voltage setting of the regulator in the upstream power supply if load current exceeds a preset limit. Finally, some lab supplies have what is called "foldback current limiting", which protects the supply against dead shorts. I have seen lab supplies with both a crowbar overvoltage protection and foldback current limiting, so that in the event of a trip, no fuse has to be replaced.
 
Last edited:

tcmtech

Banned
Most Helpful Member
So what are you trying to protect?
 

Sceadwian

Banned
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top