"C" is correct. The foldback circuit is entirely different, closer to a current regulator, and for a much different purpose. The foldback operation is to limit current when there is an overload, while the "crowbar" is to short circuit the output when the regulator circuit fails. They are not even similar.

 

Update
I've already tested the circuit It's working very well
Thank you for your advices.

Yes, that should work.

 

"C" is correct. The foldback circuit is entirely different, closer to a current regulator, and for a much different purpose. The foldback operation is to limit current when there is an overload, while the "crowbar" is to short circuit the output when the regulator circuit fails. They are not even similar.

I don't particularly agree with that premise, as long as the circuit shuts the power supply off, whether permanently or just shuts it down until the over-voltage is not present comes within the definition.
There are more than a few links out there that agree.

Quote:
"A crowbar circuit is usually placed across the power supply’s output terminals, to protect the load against any overvoltage. It does this by shorting the terminals (placing a crowbar across) which deactivates the protection device. It may blow up the fuse, trip the circuit breaker or shut down some parts of the circuit so as to cut off the power to the load.. "

 

There are also over-voltage protection devices and schemes around, no doubt. But i every instance where a crowbar circuit is added, it is stated to be protection against regulator failure, usually in the form of pass transistor short circuiting. I have a nice lab power supply that has an adjustable over voltage protection somehow included. That function is very adjustable and quite different from it's constant current mode function, which can be adjusted to operate in a voltage foldback mode.
The difference is that the OVP function is not like a crowbar function.

 

Well a system that folds back the power supply in the event of an over voltage and does not reset or retry until power is turned off and restored, can still be termed a Crowbar.
It all comes down to your personal interpretation!

 

Foldback does not work if the pass transistors short circuit. THAT is a job for the crowbar system.

 

Hammond used to make a series of regulated linear power supplies, some of which had crow-bar protection, these did not blow a fuse etc, they just had a fold back circuit, active as long as the over-voltage was present.

I presume that you mean that they had a thyristor crow-bar as over-voltage protection, but also a foldback current limiter that meant that the device could resume operation as soon as the over-voltage situation was removed.
It would operate the same was as a thyristor crow-bar protected by a PTCC fuse.

 

Well a system that folds back the power supply in the event of an over voltage and does not reset or retry until power is turned off and restored, can still be termed a Crowbar.
It all comes down to your personal interpretation!

Only if the interpretation is consistent with the common interpretation, and yours is not.
It may prevent most over-voltages but it's not a crowbar circuit.

This from Wikipedia, which is the general definition:
A crowbar circuit is an electrical circuit used for preventing an overvoltage or surge condition of a power supply unit from damaging the circuits attached to the power supply. It operates by putting a short circuit or low resistance path across the voltage output (Vo), like dropping a crowbar across the output terminals of the power supply.

The circuit needs to be independent of the regulating circuit so it can prevent the overvoltage, even when the regulator fails.

 

Only if the interpretation is consistent with the common interpretation, and yours is not.
It may prevent most over-voltages but it's not a crowbar circuit.

This from Wikipedia, which is the general definition:
A crowbar circuit is an electrical circuit used for preventing an overvoltage or surge condition of a power supply unit from damaging the circuits attached to the power supply. It operates by putting a short circuit or low resistance path across the voltage output (Vo), like dropping a crowbar across the output terminals of the power supply.

The circuit needs to be independent of the regulating circuit so it can prevent the overvoltage, even when the regulator fails.

REally, a foldback circuit reduces the voltage to limit the current. If tghe over voltage does not cause an excess current then it does not reduce the voltage.

 

In the event of no official definition, it is open to interpretation, IMO.
Also used by the PS manuf I have used that use fold back.

 

In the event of no official definition

So, what would you consider an "official definition"?

 

Common use over the past 20 or 30 years has defined "foldback as dropping the voltage to keep current at somelimit. And crowbar, ever since the creation of series transistor regulated power supplies, has been used to describe the system that short circuits the supply when the pass transistors fail, usually by short circuit.