1541 CIRCUIT THEORY
Power Up/Down Write Protection
This circuit prevents erroneous data from being written on the disk during power up/down sequences.
During a power up, the 12VDC supply is not applied to the R/W coils and amplifier circuits before
the processor has control of the logic. During a power down the 12VDC supply is removed from the
R/W coils and amplifier circuits before the processor loses control of the logic.
Q1 acts as a series pass transistor, biased to regulate the 12VF output to the R/W coils and Amplifier
circuits. Q2 is a feedback amplifier monitoring the 5VDC supply. CR5 develops a precise reference
voltage for Q2. L8 and C15 delay the 12VDC supply.
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