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Vacuum Tubes

Vacuum Tubes. Alex Smith. What are/were they?. Two Classes of Devices. Amplifiers (Triodes, Tetrodes , and Pentodes). Diodes. Radios Power Systems Voltage Protection Logic Gates Radiation Detectors Thermometers. Signal Processing Audio Power Systems Logic Gates Radios.

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Vacuum Tubes

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  1. Vacuum Tubes Alex Smith

  2. What are/were they?

  3. Two Classes of Devices Amplifiers (Triodes, Tetrodes, and Pentodes) Diodes • Radios • Power Systems • Voltage Protection • Logic Gates • Radiation Detectors • Thermometers • Signal Processing • Audio • Power Systems • Logic Gates • Radios

  4. Vacuum Tube Diodes

  5. What you need to know • for current to flow • There is no turn-on voltage • just needs to be high enough to heat the cathode • Reverse breakdown voltage is REALLY high • I-V Curve is a little different than a solid state diode

  6. Vacuum Tube Triode

  7. What you need to know • controls current flow • Lower means less device current • Device current depends on and • Gain limited by parasitic (Miller) capacitance between plate and mesh

  8. Vacuum Tube Tetrode • Schottky added screen terminal which decoupled the plate terminal and the mesh, eliminating the Miller capacitance • Tetrode Kink • Caused by secondary electron emission • Can be used to create a negative resistance

  9. Vacuum Tube Pentode • Suppressor Grid (@ Cathode Voltage) added by Tellegen to reduce secondary electron emission • Suppressor grid captures and contains electrons trying to leave the plate terminal

  10. Power Beam Tetrode • Alternate solution to secondary emission • Incident electrons focused into pair of beams using plates and special grid/screen geometry • Better LOH performance, and more power efficient than Pentode

  11. Gas-Filled Tubes • Discharge Tubes • Hydrogen: High Speed • Deuterium: HV, High Speed • Noble Gases: Switching, Neon Lights • Mercury: HV, Low Forward Drop, Low Energy Loss • Metal Vapors Used in lasers • Halogens used as surge arrestors/protection

  12. Thyratron/Ignitron/Krytron • Used in power applications • Behaves exactly like SCR • Latches when control voltage ionizes gas, resets when Anode-Cathode voltage drops • Replaced by SCR for all but highest power applications • Krytrons used as nuclear weapon detonators

  13. Cathode Ray Tubes (CRTs) • Electron Beam from tube is bent using magnetic coils • Monitors have 3 different tubes (red, green, blue) in an “electron gun” • Frequency of light emitted depends on gas in tube

  14. References http://en.wikipedia.org/wiki/Vacuum_tube#Triodes http://sub.allaboutcircuits.com/images/03006.png http://content.answcdn.com/main/content/img/ahd4/A4triode.jpg http://www.tpub.com/neets/book6/0073.GIF http://sub.allaboutcircuits.com/images/03172.png http://images.gizmag.com/inline/nixie-chess-10.jpg http://www.learningelectronics.net/images/03018.png http://upload.wikimedia.org/wikipedia/commons/b/b0/Cathode_ray_Tube.PNG

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