HA17723 データシートの表示（PDF） - Hitachi -> Renesas Electronics
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HA17723 Datasheet PDF : 17 Pages
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HA17723/F/P
Negative Voltage Regulator: Figure 3 shows the construction of a so-called negative voltage regulator,
which generates a negative output voltage with regard to GND. Assume that the output voltage, –VOUT,
increases in the negative direction. As the voltage across the R1 is larger than that across the R3, which
provides the reference voltage, the output current of the error amplifier increases. In the control circuit, the
impedance decreases with the increase of input current, which makes the base current of the external
transistor Q approach GND. As a result, the output voltage returns to the established value and output
voltage is stable.
The output voltage –VOUT of this circuit is:
–VOUT = –
R1 + R2 × R3
R3 + R4 R1
VREF
=
–
R2
·
(R1 + R2) · (R3 + R4)
(R3 + R4) – R4 · (R1 +
R2)
×
R3
R3 + R4
VREF
R2
11.5kΩ
R4
3kΩ
R3
R1
3kΩ 3.65kΩ
VCC
VREF
VC
VOUT
VZ
CL
R5
2kΩ
VIN
Q
CS
VIN(+) VIN(–)
VEE
C1
COMP 100pF
VOUT
Figure 3 Negative Voltage Regulator
How to Increase the Output Current: To increase the output current, you must increase the current
capacity of the control circuit. Figures 4 and 5 show examples with external transistors.
VIN
VCC
VREF
VIN(+)
VEE
VC
Q
VOUT
RSC
CL
0.7Ω
VOUT
CS
R1
7.87kΩ
VIN(–)
C1
R2
COMP 500pF 7.15kΩ
Figure 4 Increasing Output Current (1)
6
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