Text-only reference. Published from the recorded official FAA General Chapter 12 PDF. Diagrams, photographs, and figure artwork are not reproduced here; use the official FAA PDF for those materials.
12-100 AC switching relay AC primary bus AC secondary bus MAIN Stdby Off Left generator DC bus Inverter switch DC power Main inverter power relay Main inverter AC bus tie breaker Weather radar From main inverter only From standby inverter only Circuit energized by standby inverter only with inverter switch set to main and radar switch set to on. RMI card RMI pointer26 VAC bus or Engine oil pressure ratio Oil pressureStandby inverter Secondary inverter power relay Right generator DC bus 115 VAC power 26 VAC power when the diode is reversed biased. Figure 12-214 shows a graph of the current characteristics of a diode that is biased in both directions.
Rectifiers
Many devices in an aircraft require high amperage, low voltage DC for operation. This power may be furnished by DC engine-driven generators, motor generator sets, vacuum tube rectifiers, or dry disk or solid-state rectifiers. In aircraft with AC systems, a special DC generator is not desirable since it would be necessary for the engine accessory section to drive an additional piece of equipment. Motor generator sets, consisting of air-cooled AC motors that drive DC generators, eliminate this objection because they operate directly off the AC power system. Vacuum tube or various types of solid-state rectifiers provide a simple and efficient method of obtaining high voltage DC at low amperage.
Dry disk and solid-state rectifiers, on the other hand, are an excellent source of high amperage at low voltage. A rectifier is a device that transforms AC into DC by limiting or regulating the direction of current flow. The principal types of rectifiers are dry disk and solid state. Solid-state, or semiconductor, rectifiers have replaced virtually all other types; and, since dry disk and motor generators are largely limited to older model aircraft, the major part of the study of rectifiers is devoted to solid-state devices used for rectification. The two methods discussed in this handbook 12-101 Gear control Flaps Spoiler Wheel master Nose steering relay Yaw trim Altitude gyro Auxiliary battery Normally closed relay Directional gyro Roll trim ADF On (MOM) Off Gear, flap, spoiler switch Pilot’s audio Copilot’s map light Transceiver On Off Gyros Battery Inverter Right fwd bus Transceiver light Altitude gyro light Directional gyro light Resonant filter regulator Output keyer Buffer amplifier DC regulator Square wave oscillator DC input AC output are the half-wave rectifier and the full-wave rectifier.
Half-Wave Rectifier rectifier. When an AC signal is on a positive swing as shown in Figure 12-215A, the polarities across the diode and the load resistor are also positive. In this case, the diode is forward biased and can be replaced with a short circuit as shown in the figure. The positive portion of the input signal appears across the load resistor with no loss in potential across the series diode. Note that the polarities across the diode and the load resistor are also reversed. In this case, the diode is now reverse biased and can be replaced with an equivalent open circuit. The current in the circuit is now 0 amperes and the voltage drop over the load resistor is 0 volts. The resulting waveform for a complete 12-102 Si Si Si SiSi SiSiSi Si A B Electron movement Silicon atom showing one of the electrons in its valence shell Silicon atom in which one electron has broken out of its valence shell and left a hole Electron moving from one silicon atom to another and leaving a hole Hole movement N-typeP-type N-typeDepletion zone Represents electrostatic field P-type sinusoidal input can be seen at the far right of Figure 12-215.
The output waveform is a reproduction of the input waveform minus the negative voltage swing of the wave. For this reason, this type of rectifier is called a half-wave rectifier. Full-Wave Rectifier a rectifier. This type of a rectifier is called a full-wave bridge rectifier. The term “full-wave” indicates that the output is a continuous sequence of pulses rather than having gaps that appear in the half-wave rectifier. positive portion of the input signal is applied to the network. Note the polarities across the diodes. Diodes D2 and D4 are reverse biased and can be replaced with an open circuit.
Diodes D1 and D3 are forward biased and act as an open circuit. The current path through the diodes is clear to see, and the resulting waveform is developed across the load resistor. During the negative portion of the applied signal, the diodes reverse their polarity and bias states. The result is a network shown in Figure 12-216D. Current now passes through diodes D4 and D2, which are forward biased, while diodes D1 and D3 are essentially open circuits due to being reverse biased. Note that during both alternations of the input waveform, the current passes through the load resistor in the same direction.
This results in the negative swing of the waveform being flipped up to the positive side of the time line. Dry Disk Dry disk rectifiers operate on the principle that electric current flows through a junction of two dissimilar conducting materials more readily in one direction than it does in the opposite direction. This is true because the resistance to current flow in one direction is low, while in the other direction it is high. Depending on the materials used, several amperes may flow in the direction of low resistance but only