Text preview for : 3-Power_Supplies.pdf part of Mitsubishi VS-50805, WT-60805, WS-55905, WS-65905, WS-73905, WS-55805, WT-46805 Mitsubishi VS-50805, WT-60805, WS-55905, WS-65905, WS-73905, WS-55805, WT-46805 (Chassis V16 N W) (Training Manual + Schematic)
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Chapter 3 Power Supplies
Power supply circuitry in the V16 chassis is conventional for high performance projection televisions. Topics covered in this chapter include: Standby Power Supplies Switched Power Supplies Block diagrams are provided to assist in servicing these circuits.
The Standby Power Supply not only supplies circuits that require power while the TV is not in use, some of the sources are also used as switched supplies. This requires a slightly more complex circuit. Standby Power Supply Regulation Figure 3-1 shows a simplified diagram of the Standby Regulator circuitry. The basic operation of the Regulator is the same as that in previous models. The key points of the Regulators operation are as follows: Start-up Voltage 16.5V from R917 provides start-up voltage for the oscillator. Run Voltage Voltage produced by the secondary at D914 sustains the oscillators DC supply as the IC starts to draw current.
Standby Power Supplies
Over Voltage Protection If Pin 4 exceeds 20.5V, the IC will shut down. Regulation Feedback The 31.5V Supply is the monitored source. Feedback is coupled by PC900 back to Pin 1 of the IC. Over Current Protection Pin 1 of IC951 is also the Over Current Protect input. The internal FETs ground return is at pin 2 of the IC. The voltage drop across R955 and R956 indicates the FETs current. It is coupled through R953 to pin 1 of the IC. The Over Current Protect circuit is activated if the voltage at pin 1 of the IC exceeds 1.35 volts. Three Standby Supplies and one Switched Supply are directly generated by rectifying signal from the secondary windings of T900; Standby voltages 34 Volts, 31.5, Volts 12 Volts and Switched 32 Volts.
The Switched 32 Volt supply furnishes power to the Vertical Output IC. The Standby 34 Volts is for the Audio Output. The 31.5 Volt Supply is the source for the: Tuning voltage Standby 12 Volt supply Switched 12 Volt Supply Switched 5 Volt Supply The three switched supplies are only activated when the POWER-ON line goes HIGH, driving Q924 into conduction. The conduction of Q924 enables
IC922, and Q925. IC922 generates the 5VSW supply, and Q925 the 12VSW supply. The POWERON line also feeds Q921, Q922 and Q923 to switch the 32VSW source. Standby Power Supply Distribution Overall Distribution of the Standby Power Supplies is shown in Figure 3-2. The diagram shows the source of each of the Standby Supplies, and the major circuits using that supply. If a DC voltage is missing in a circuit, the diagram in Figure 3-2 will help to quickly locate the source of that supply.
The Switched Power Supply is similar to the Standby Power Supply. Figure 3-3 diagrams both the regulator and the distribution of the supplies produced. On-Off Switching On-off switching is provided by the relay, K9A30 and the relay driver, Q9A30. The Power-on command is generated by the Main uPC, IC700. When first switched on, initial surge current is limited by R9A01, 1.8 ohms. After the Switched 34 volt supply is developed, K9A31 is activated, shunting the resistor, allowing full current to be supplied to the regulator and subsequent circuits.
Switched Power Supplies
Regulation Operation of the regulator, IC9A00, is identical to the standby power supply, with component responsibilities assigned as follows: Start-up Voltage 16.5V from R9A14. Run Voltage produced by the secondary at D9A08. Regulation Feedback The 115V Supply is the monitored source. Feedback is coupled by PC9A00 to Pin 1 of the IC. Over Current Protection Pin 1 of IC9A00 is also the Over Current Protect input. The internal FETs ground return is at pin 2 of the IC. The voltage drop across R9A04, R9A15 and R9A16 indicates the FETs current. It is coupled through R9A05 to pin 1 of the IC.
Switched Power Supply Distribution Switched Power Supply distribution is shown in Figure 3-4. As discussed in the Standby Supply,
the diagram shows the source of each of the Switched Supplies. Use the diagram in Figure 3-4 to quickly locate the source of a missing supply.