Maker Pro
Maker Pro

Why seperate overvoltage and overcurrent protection?

U

Ultimate Buu

Jan 1, 1970
0
Most telecoms equipment have both fuses and thyristor like device for
overcurrent and overvoltage protection respectively. Why is this? Most
overvoltage situations will result in overcurrent as wel, right? Unless the
device isn't connected, I guess, and an open circuit exists.
 
W

Walter Harley

Jan 1, 1970
0
Ultimate Buu said:
Most telecoms equipment have both fuses and thyristor like device for
overcurrent and overvoltage protection respectively. Why is this? Most
overvoltage situations will result in overcurrent as wel, right? Unless the
device isn't connected, I guess, and an open circuit exists.

A fuse blows relatively slowly. It helps keep a device from catching on
fire in the event of an internal or downstream failure that causes it to
draw excessive current. It can also help ensure that in the event of an
internal failure, a device does not present a shock hazard. It does not
often protect a device from getting damaged; it just keeps the damage from
spreading.

An MOV or other overvoltage protector triggers very quickly. It helps
protect the device from getting damaged by external factors such as power
surges.
 
C

Charles Schuler

Jan 1, 1970
0
Ultimate Buu said:
Most telecoms equipment have both fuses and thyristor like device for
overcurrent and overvoltage protection respectively. Why is this? Most
overvoltage situations will result in overcurrent as wel, right? Unless the
device isn't connected, I guess, and an open circuit exists.

A crowbar circuit is a nice feature with a linear pass regulator. If the
pass element shorts, the full unregulated input voltage can appear across
the output and possibly destroy expensive circuits. Crowbars are often SCRs
which are triggered when the regulated output goes to some predetermined
level. To summarize, a crowbar protects loads from a regulator failure and
the overcurrent circuit protects the power supply in the case of a shorted
load. Having both is a good idea.
 
T

Tom Bruhns

Jan 1, 1970
0
Ultimate Buu said:
Most telecoms equipment have both fuses and thyristor like device for
overcurrent and overvoltage protection respectively. Why is this? Most
overvoltage situations will result in overcurrent as wel, right? Unless the
device isn't connected, I guess, and an open circuit exists.

Cuz by then it's too late?? The current may only go up slowly with
increased voltage, depending on the device. The fuse is likely rated
for quite a bit more than the nominal current, to allow for starting
surges, etc. You likely would have to get the voltage to levels that
would destroy the semiconductors (or other parts) before the current
became great enough to blow the fuse. OTOH, if you take it that high,
it's pretty likely to blow the fuse.... ;-)

Cheers,
Tom
 
Top