Switching Power Supply - Basic Configuration
Figure 018
1EFF : 106-149, 303-399, 1 31-63-00Page 55 1 1 Config-3 Aug 01/05 1 1 1CES 1 The A/C power supply 115 V/400 Hz is filtered and full-wave rectified. This rectified voltage Vin is applied to the boost switching regulator, which consists basically of a MOSFET T1, a power inductor L, a diode D2 and filter capacitors C1, C2. When the MOSFET T1 is switched on, under control of the boost controller, the voltage Vin is applied directly across the power inductor L. Energy is thus transferred from the input supply to the power inductor. When the MOSFET T1 is turned off by the boost controller, the energy stored in the power inductor induces a voltage such that the diode D2 conducts and transfers this energy to the half bridge circuit. The voltage Vout developed in this way by the boost switching regulator is considerably higher than its input voltage Vin. The half bridge circuit operates as a high frequency switcher and delivers high output power to the output transformer. It is controlled by the half bridge controller, which transmits pulses with variable pulse-widths. The AC voltages transformed by the output transformer are rectified, filtered and regulated by the output voltage generators in order to supply the various DC voltages.
B. CRT
(1)
Cathode Ray Tube assembly The CRT assembly is located in the central part of the DU structure. The CRT is a Shadow-Mask color CRT potted with resin and surrounded by a metal shield. The CRT is equipped with flying leads ended by a connector, VHV lead and two photo-resistor cells.
(2)
VHV power supply The VHV Power Supply is located on the lower part of the display unit. It provides all the voltages required by the CRT : anode G4, focusing electrode G3, preacceleration anode G2. It also includes the control input (VHV INH) and a test output. A defocusing circuit controls the focusing electrode. It is able to thicken the electron beam for the drawing of coloured areas.
(3)
Analog board
The Analog Board consists of the main following functions :
(Ref. Fig. 019)
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CRT - Analog Board - Block Diagram
Figure 019
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-cathode amplifiers and gamma correction
-brightness control
-G1 control (grid inhibition)
-deflection and convergence amplifiers and corrections
-monitoring, protection and orbiting circuits.
(a) Cathode amplifiers and gamma correction
1_ Gamma correction
The CRT has a non-linear relationship between the beam current
and the cathode voltage.
The beam current versus cathode voltage characteristics curve
IK = f(VGK), for each gun must be linearized in order to
compensate for this function. This is achieved by an inverse
mathematical function which compensates for the curve
inflection due to the CRT characteristics. Correction is
provided by a circuit which generates a modulation current
proportional to VGK.
2_ Cathode amplifier
Each cathode of the CRT to which is applied the
chrominance/luminance signal is driven by a voltage.
The modulation current available on the output of the gamma
correction circuit, is converted to the voltage VGK.
The conversion is performed by three hybrid cathode amplifiers
(one per gun).
These amplifiers are driven by the output current from the
gamma correction circuit. The cathode modulation voltage is
generated from the modulation current by means of the cathode
amplifier feed-back circuit.
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(b) Brightness control Correct picture display requires brightness control because of the changing environmental lighting conditions in the cockpit, and the different drawing speeds for the stroke written symbology and for the background colored areas. A first correction is made manually with the brightness potentiometer which enables the crew to adjust the general brightness level. A second correction is performed automatically according to the environmental lighting. The environmental lighting is measured on the front panel of the display unit by two light sensors, which provide a voltage proportional to the received lighting flux. The brightness modulating the electronic beam takes simultaneously into account these controls and corrections. During test of the red gun, the brightness control is replaced by a fixed voltage. To provide these capabilities, the brightness control circuit is organized as follows :
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