Garmin GAD 42 Maintenance Manual - Page 6

5.2 CPU PC Board The CPU PC Board contains the unit microprocessor and support circuitry, as well as two field programmable gate array (FPGA) integrated circuits. Digital and discrete I/O circuitry is located on this PC board, and interfaces to other avionics (none provided) through a 62-pin high-density D-subminiature aircraft interface connector. Three 18-pin header board connectors provide interconnect to the Analog PC board assembly. 6.0 BLOCK DIAGRAM Figure 1, page 12, shows a block diagram of the GAD 42 to aid in understanding the theory of operation. 7.0 BASIC THEORY OF OPERATION 7.1 Power Supplies 7.1.1 Power Input Circuitry DC aircraft power input to the GAD 42 is input to the aircraft interface connector on the Analog PC Board. This connector also provides a return path to aircraft ground. Power input is routed directly to the superflag output drivers through a three-amp superflag input fuse. This fuse protects the superflag drivers. Also protecting the superflag drivers from overvoltage transients is a transient suppression zener. Power input is also routed through a five-amp power supply input fuse to an input filter, which provides power to the unit power supplies. Protecting this filter from overvoltage transients is a transient suppression zener. The power-input filter is a low pass filter formed by an inductor and the parallel combination of power supply input electrolytic capacitors. This same inductor forms an output low pass filter with ceramic capacitors on the input side to prevent high frequencies generated by the power supplies from exiting the unit on the power line. 7.1.2 Main Power Supply The main power supply is a flyback topology switcher controlled by an integrated current-mode controller and switch operating at a fixed frequency of 100 kHz and producing the following output voltages: • +20 V • +12 V • -12 V • -20 V • +34 V GAD 42 MAINTENANCE MANUAL P/N 190-00159-01 Page 5 Rev. A