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50µF
-
capacitors C2 and C4 are pump and reservoir respectively
V-
for the doubled positive voltage. There is a penalty in this
FIGURE 24. SPLITTING A SUPPLY IN HALF
configuration which combines both functions, however, in
that the source impedances of the generated supplies will be
somewhat higher due to the finite impedance of the common
50K
+8V
charge pump driver at pin 2 of the device.
56K
Voltage Splitting
-
10µF
+8V
+
100&!
The bidirectional characteristics can also be used to split a
50K
-
higher supply in half, as shown in Figure 24. The combined
ICL7611
100K
load will be evenly shared between the two sides and, a high
+
value resistor to the LV pin ensures start-up. Because the
1 8
switches share the load in parallel, the output impedance is
2 7
ICL7662
much lower than in the standard circuits, and higher currents
+
ICL8069
100µF 3 6
can be drawn from the device. By using this circuit, and then
-
the circuit of Figure 19, +30V can be converted (via +15V, 4 5
VOUT
and -15V) to a nominal -30V, although with rather high series
output resistance (~250&!).
-
800K
250K 100µF
+
VOLTAGE
Regulated Negative Voltage Supply
ADJUST
In some cases, the output impedance of the ICL7662 can be a
FIGURE 25. REGULATING THE OUTPUT VOLTAGE
problem, particularly if the load current varies substantially. The
circuit of Figure 25 can be used to overcome this by controlling
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