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Crowbar (circuit)
 
 
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A crowbar circuit is an electrical circuit used to prevent an overvoltage condition of a power supply
Power supply

Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output External electric load or group of loads is called a power supply unit or PSU....
 unit from damaging the circuits attached to the power supply. It operates by putting a short circuit
Short circuit

A short circuit in an electrical circuit that allows a Electric current along a different path from the one intended.The electrical opposite of a short circuit is an "open circuit", which is an infinite resistance between two nodes....
 or low resistance path across the voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 source, much as if one dropped a tool of the same name
Crowbar (tool)

A crowbar, pry bar, or prybar, more informally a jimmy, jimmy bar, jemmy or gooseneck is a tool consisting of a metal pole with a single curved end and flattened points, often with a small fissure on one or both ends for removing nail ....
 across the output terminals of the power supply. Crowbar circuits are frequently implemented using a thyristor
Thyristor

The thyristor is a Solid state semiconductor device with four layers of alternating N-type semiconductor and P-type semiconductor material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased ....
 (also called an SCR) or a trisil
Trisil

A Trisil is trade name for a thyristor surge protection device, an electronic component designed to protect electronic circuits against overvoltage....
 or thyratron
Thyratron

A thyratron is a type of gas filled tube used as a high energy electrical switch and controlled rectifier. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design....
 as the shorting device.






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Encyclopedia


A crowbar circuit is an electrical circuit used to prevent an overvoltage condition of a power supply
Power supply

Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output External electric load or group of loads is called a power supply unit or PSU....
 unit from damaging the circuits attached to the power supply. It operates by putting a short circuit
Short circuit

A short circuit in an electrical circuit that allows a Electric current along a different path from the one intended.The electrical opposite of a short circuit is an "open circuit", which is an infinite resistance between two nodes....
 or low resistance path across the voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 source, much as if one dropped a tool of the same name
Crowbar (tool)

A crowbar, pry bar, or prybar, more informally a jimmy, jimmy bar, jemmy or gooseneck is a tool consisting of a metal pole with a single curved end and flattened points, often with a small fissure on one or both ends for removing nail ....
 across the output terminals of the power supply. Crowbar circuits are frequently implemented using a thyristor
Thyristor

The thyristor is a Solid state semiconductor device with four layers of alternating N-type semiconductor and P-type semiconductor material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased ....
 (also called an SCR) or a trisil
Trisil

A Trisil is trade name for a thyristor surge protection device, an electronic component designed to protect electronic circuits against overvoltage....
 or thyratron
Thyratron

A thyratron is a type of gas filled tube used as a high energy electrical switch and controlled rectifier. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design....
 as the shorting device. Once triggered, they depend on the current-limiting circuitry of the power supply or, if that fails, the blowing of the line fuse
Fuse (electrical)

In electronics and electrical engineering a fuse is a type of overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows, which breaks the electrical network in which it is connected, thus protecting the circuit's other components from damage due to excessive current....
 or circuit breaker
Circuit breaker

A circuit breaker is an automatically-operated Electricity switch designed to protect an Electrical network from damage caused by Overcurrent or short circuit....
.

A crowbar circuit is distinct from a clamp
Clamp (circuit)

A clamp or clamp circuit is an electrical circuit used to prevent another circuit from exceeding a certain predetermined voltage level. It operates by sensing the output voltage of the monitored circuit and then as the output voltage approaches the preset limit, applies an electric load which draws greater and greater current from the...
 in that, once triggered, it pulls the voltage below the trigger level, usually close to ground
Ground (electricity)

In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
. A clamp prevents the voltage from exceeding a preset level. Thus, a crowbar will not automatically return to normal operation when the overvoltage condition is removed; power must be removed entirely to stop its conduction.

An active crowbar is a crowbar that can remove the short circuit when the transient is over thus allowing the device to resume normal operation. Active crowbars use instead of a thyristor a transistor, gate turn off (GTO) thyristor or forced commutated thyristor to short the circuit. Active crowbars are commonly used to protect the frequency converter in the rotor circuit of the doubly fed generators
Doubly-fed electric machine

Doubly-fed electric machines belong to a category of electric machines that incorporate two polyphase coil winding sets of similar power rating that have independent means of excitation....
 against high voltage and current transients caused by the voltage dips in the power network. Thus the generator can ride through the fault
Low voltage ride through

In Electrical power industry,low voltage ride through , or ride through faults, is what an electric device, especially wind generator, may be required to be capable of when the voltage in the Electric power transmission is temporarily reduced due to a fault or load change in the grid....
 and quickly continue the operation even during the voltage dip.

The advantage of a crowbar over a clamp is that the low holding voltage of the crowbar lets it carry higher fault current without dissipating much power (which could otherwise cause overheating). Also, a crowbar is more likely than a clamp to deactivate a device (by blowing a fuse or tripping a breaker), bringing attention to the faulty equipment.

The term is also used as a verb to describe the act of short-circuiting the output of a power supply.

Applications

High voltage crowbars are used for HV tube (Klystron
Klystron

A klystron is a specialized Linear particle accelerator vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern particle accelerators....
 and IOT
Inductive output tube

The inductive output tube or IOT is a variety of vacuum tube which evolved in the 1980s to meet increasing efficiency requirements for high-power radio frequency amplifiers....
) protection.

Manufacturers

  • Manufacturer of thyristors
  • Manufacturer of thyristors
  • Manufacturer of semiconductor-based replacements for thyratrons
  • Manufacturer of high-voltage thyratrons