Write Ckt Block Diagram - Quantum Q2080 Product Description

WRITE GATE
DRI SE.(
SEEK COM
+5V
WRITE
ENABLE
SWITCH
+24 V
,
WRITE
ENABLE--., CURRENT
... SOURCE
REDUCE WRITE CURRENT
+
MFM WD
-MFMWD
WRITE
DATA
RCVR
WRITE I
,
WRITE
~-----1H---4 DR IV E R
HEAD 2° ...
HEAD 21 ...
HEAD
22 ...
-
HEAD
SELECT
- ' -
FIGURE 1-27
..
J
I
.1
1
1 OF
7
WRITE
CURRENT
DETECT
HEAD CENTER TAPS
WRITE CKT BLOCK DIAGRAM
WRITE FAULT
...
-
This constant current source provides the write driver with 18 rnA of write current. The circuit also provides a
current-on signal that is used by the write current detector to set the write fault flip-flop. The write driver receives its
switching input from the write data receiver. The write driver switches the write current into one end or the other end
of the head coil whose center tap has been grounded by the head select switch. The head select switch then grounds
the selected head center tap.
Figure 1-28 is a simplified schematic of the write enable switch which is shown in greater detail on Figure 2-2,
location A and B, 5 through 8. The logic to generate
+
WRITE is found on Figure 2-2, location A and B, 1 through
8. Transistor Q3 is the current enable switch that will turn on when current flows through R9, causing Q3's base to be
less positive than its emitter. In order for current flow in R9 transistor Q4 must conduct. Q4 conducts when the
+
5V
is greater than 3.5V due to the action of R13, the base emitter junction of Q4, and CR12 (3.0V zener diode); and the
+
WRITE signal is true. The
+
WRITE signal will only be true if all of the following conditions are met:
1. The drive is selected (U4F-4HI)
2. WRITE GATE is true (U4F-5HI)
3. SEEK COMPLETE is true (U4D-2HI)
When these conditions are met, current is supplied to the constant current source Q2 via the current setting
resistor R15. Diodes CR3 and CR16 set a reference voltage across R15 and Q2 to maintain a constant current flow
through Q2 during voltage fluctuations of the
+
24V supply. Resistors R17 and R20 provide a current path for the
write driver to shut off when Q3 is turned off. The write driver switches the write current between the windings of the
selected head.
1-25 REV A (01/84)