Get On Board with. Compass Card. Compass Card is the smart card and smart choice for transit passes in the San Diego region. Compass Card is your ticket for the Bus, TROLLEY, COASTER, and SPRINTER.ompass Card. Compass Card is the smart card and smart choice for transit passes in the San Diego region. Compass Card is your ticket for the Bus, TROLLEY, COASTER, and SPRINTER.
Electron (or Vacuum) Tubes. An electron tube (also known as a 'Vacuum tube', or a 'Valve' ) is a glass or metal enclosure in which electrons move through the vacuum or gas from one metal electrode to another. The vacuum tube is often used to amplify weak currents or act as a one-way valve (rectifier) for electric current. Before the 1947 invention of the transistor the electron tube was the basis of virtually all electronic devices. The simplest kind of electron tube is the diode, which was invented in 1904 by John A. Fleming.
Operation of Zener Diode: 1  Zener diodes are normally used only in the reverse bias direction. 2  It means that the anode must be connected to the negative side of the voltage source and the cathode must be connected to the positive side. Varying amount of reverse current can pass through the diode without damaging it. 2  The breakdown voltage or zener voltage (VZ) across the diode remains relatively constant. 3  The maximum reverse current is limited, however, by the wattage rating of the diode.