TM 9-6115-669-13&P
1.14.5 Internal Power Supply.
PDU switching elements and lamps are designed for an internal operating voltage of +24 VDC. The
internal operating voltage is delivered from the generators and/or generated by a power supply in
the PDU. Voltage from the generators is fed by buffer diodes V1, V2 (figure 1-12) directly into the
internal line power system. This feed operates during the activation phase when the generator
power system is not yet supplying voltage. Once the generator has reached operating speed, voltage
is present at PDU bus bars L1, L2, L3. This voltage is transformed by T13 and rectified by V5,
making available an internal power supply of approximately +26 VDC during steady-state
operation. The voltage then increases from approximately +24 VDC to approximately +26 VDC. If
power supply T13/V5 fails, diodes V1, V2 once again supply power operation is maintained.
1.14.6 Indicator Lamp Circuits.
The PDU contains a cabinet lighting system with lamp H12. Opening the access door closes switch
S5, activating the interior cabinet lighting.
Control panel lamps H1 to H11 are powered from a brightness control N7 (figure 1-12) in the form
of a dimmer circuit. Lamp brightness is set with PANEL DIMMER potentiometer R1. LAMP TEST
pushbutton switch S1 is used for lamp testing. The lamps contain two diodes which switch them
either for operation (e.g. relay contact 43/44 of K12 for lamp H10), or for lamp testing.
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