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DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 19 of 80
+5V Supply Generation
This DC-DC converter will operate from a supply between 8V to 55V and produces an output voltage of between
3.3V and 50V depending on the value of R747. For an output of 5V, R747 must be 2k7Ω. C741 connected to pin 3
provides a soft-start routine. If pin 3 is held low then the device will not operate. The frequency of the internal
oscillator is fixed by the value of R706 and C735. Over-current and over-voltage protection are incorporated
into the design of this device.
3.3V and 50V depending on the value of R747. For an output of 5V, R747 must be 2k7Ω. C741 connected to pin 3
provides a soft-start routine. If pin 3 is held low then the device will not operate. The frequency of the internal
oscillator is fixed by the value of R706 and C735. Over-current and over-voltage protection are incorporated
into the design of this device.
Figure 9: +5V Generation Circuit
+3.3V Supply Generation
As the processor in this chassis runs at 3.3V (pins 7, 28, 38, 49 and 78), it is necessary to change the 5V supply.
A series regulation circuit comprising of Q710, Q711 and Q712 provides this function.
A series regulation circuit comprising of Q710, Q711 and Q712 provides this function.
Figure 10: 3.3V Regulation Circuit
Sharp Electronics (UK) Limited - May 2003
Revision 3
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