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Measuring the supply voltage with a voltmeter, everything checks out well. There does not appear to be an overvoltage condition causing a legitimate "crowbar" event in the circuit. Disconnecting the load from the crowbar circuit and powering it up with a standard bench-top laboratory power supply reveals the load to be in perfect condition. Thus, both the source and the load have been eliminated as possibilities that may have blown the fuse(s). | Thyristor application circuits This worksheet and all related files are licensed under the Creative Commons Attribution License version 1.0. To view a copy of this license visit http creativecommons.org licenses by 1.0 or send a letter to Creative Commons 559 Nathan Abbott Way Stanford California 94305 USA. The terms and conditions of this license allow for free copying distribution and or modification of all licensed works by the general public. Resources and methods for learning about these subjects list a few here in preparation for your research 1 Questions Question 1 The following schematic diagram shows a simple crowbar circuit used to protect a sensitive DC load from accidental overvoltages in the supply power V Here the UJT serves as an overvoltage detection device triggering the SCR when necessary. Explain how this circuit works and what the function of each of its components is. file 02143 Question 2 The circuit shown here indicates which pushbutton switch has been actuated first. After actuating any one of the three pushbutton switches and energizing its respective lamp none of the other lamps can be made to energize Lamp. SW1 SW2 SW2 Explain how this circuit works. Why can t any of the other lamps turn on once any one of them has been energized Also explain how the circuit could be modified so as to provide a reset to turn all lamps off again. file 01096 2 Question 3 This crowbar circuit has a problem. It used to work just fine and then one day it blew the fuse. Upon replacing the fuse the new fuse immediately blew Measuring the supply voltage with a voltmeter everything checks out well. There does not appear to be an overvoltage condition causing a legitimate crowbar event in the circuit. Disconnecting the load from the crowbar circuit and powering it up with a standard bench-top laboratory power supply reveals the load to be in perfect condition. Thus both the source and the load have been eliminated as possibilities that may have blown the fuse s . .
