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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 a transistor, gate turn off (GTO) thyristor or forced commutated thyristor instead of a thyristor to short the circuit. Active crowbars are commonly used
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of the LM431. Since this voltage is below the minimum reference voltage of the LM431, it remains off and very little current is conducted through the LM431. If the cathode resistor is sized accordingly, very little voltage will be dropped across it and the TRIAC gate terminal will be essentially at
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that acts as a crowbar circuit in the door latch assembly. This monitor switch will absolutely prevent the magnetron from being energized with the door open by short circuiting the mains supply to the magnetron. Applying power with the monitor switch closed will blow the main fuse and ruin the
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voltage. 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 allow the crowbar to return to its neutral state.
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circuit -- the PMOS half of a pair lingering in a near on-state when only its corresponding NMOS is supposed to be on (or the NMOS when the PMOS is supposed to be on) -- resulting in a near short-circuit current between supply rails.
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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.
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will begin to draw current. The voltage at the gate terminal will be pulled down, exceeding the gate trigger voltage of the TRIAC and latching it on.
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provide the reference voltage for the LM431. The divider is set so that during normal operating conditions, the voltage across R
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The name is derived from having the same effect as throwing a crowbar over exposed power supply terminals to short the output.
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The term is also used as a verb to describe the act of short-circuiting the output of a power supply, or the malfunction of a
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The advantage of a crowbar over a clamp is that the low holding voltage of the crowbar lets it carry higher
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across the output terminals of the power supply. Crowbar circuits are frequently implemented using a
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in that, once triggered, it pulls the voltage below the trigger level, usually close to
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unit from damaging the circuits attached to the power supply. It operates by putting a
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against high voltage and current transients caused by the voltage dips in the
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This article is about the electrical circuit. For other uses, see
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In the following example crowbar circuit, the LM431 adjustable
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have a crowbar circuit to protect the connected equipment.
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to protect the frequency converter in the rotor circuit of
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as the shorting device. Once triggered, they depend on the
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used for preventing an overvoltage or surge condition of a
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Article about design of thyristor-based crowbar circuits
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378:"How does the Monitor Switch in a Microwave Work?"
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417:The Art of Electronics, Second Edition
396:The Art of Electronics, Third Edition
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435:IPP Garching 80kV/14kA Crowbar from
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