2-5. POWER SUPPLY
The power supply is a pulse width modulator de-de converter. It operates from the aircraft 28 V dc bus. It
supplies multiple dc outputs. Its output voltages are as follows:
DC Output Voltage
3.0 (2.70 to 3.3)
5.0 (4.75 to 5.25)
6.75 (6.55 to 6.95)
10.0 (9.7 to 10.3)
13.0 (12.5 to 14.4)
80.0 (64.0 to 96.0)
-10,0 (-9.7 to -10.3)
-22.0 (-19.8 to -24.2)
Figure 2-2 is a functional block diagram of the power supply.
The 28 V dc input is filtered and protected against transients, overvoltage, and reverse voltage.
A multi-output de-de converter has outputs of 10 V dc, +13 V dc, +10 V dc, +3 V dc, +80 V dc, -22 V dc, and
+6.75 V dc. The +6.75 V dc output is sampled, and the sample is returned to a pulse width modulator. The pulse
width modulator regulates dc output by varying pulse width in the de-de converter. Additional regulators are used
on the -10 V dc, +10 V dc, +80 V dc, and -22 V dc outputs. A current limiter senses overcurrent conditions and
shuts down the de-de converter.
The +VHOLD output is used by rt memory circuits. It normally comes from the +6.75 V dc output. The +VHOLD
regulator supplies +VHOLD when the de-de converter is shut down.
The +5 V dc output comes from a separate regulator and current limiter. A reference voltage is taken from the
pulse width modulator.
A control switch turns the power supply on/off either from a remote control unit (POWER ON/OFF) or from a local
control panel (SWITCHED +28 V dc). The POWER ON/OFF is also used by the data rate adapter (dra). A diode
between SWITCHED +28 V dc and POWER ON/OFF allows SWITCHED +28 V dc to control the dra in local control
The standby switch shuts down the multi-output de-de converter when the FUNCTION switch is set to OFF. The +5
V dc output and +VHOLD outputs remain on.
The holding battery powers selected rt memory circuits when the aircraft +28 V dc is off or the rt is disconnected.
The holding battery switch circuit connects the holding battery except when the FUNCTION switch is in Z-A or
STOW. HB (holding battery) ON and HB OFF come from the front panel. ZA input at pin 6 is also needed to turn
the holding battery off. This assures that the holding battery is not accidentally turned off during power up. An
external holding battery may also be connected via pin 13.
2-6. RT CHASSIS
The rt chassis (A11) includes the backplane assembly and right and left card guide panels. Ten modules (A1
through A10) plug into the backplane. The front panel (A1), amplifier-oscillator (A9), and power supply (A10)
complete the rt. (See figure 2-3.) The amplifier-oscillator houses the system and ancillary connectors J1 and J2.
They connect to the backplane through a flex cable. A cover closes the top of the rt and covers the right and left
Also on the backplane are an audio transformer for receiver audio, a relay circuit that grounds the homing
indicator when not in homing mode, an integrated circuit latch on the power supply standby input, and a clock
divider for the power supply.