Typical Applications
(Continued)
R4, C3 and C4 are necessary for continuous operation and
are typically 220 kΩ, 20 pF, and 0.0022 µF respectively.
C1 is the timing capacitor found in
Figure 1.
C2
≥
I
o
(V
o
− V
in
)/(f
osc
V
o
V
ripple
).
D1 is a Schottky type diode such as a IN5818 or IN5819.
L1 is found as described in the buck converter section, using
the inductance chart for
Figure 16
for the boost configuration
and 20% discontinuity.
INVERTING REGULATOR
DS008711-9
FIGURE 18. Basic Boost Regulator
The circuit of
Figure 19
converts a 5V supply into a 15V sup-
ply with 150 mA of output current, a load regulation of 14 mV
(30 mA to 140 mA), and a line regulation of 35 mV (4.5V
≤
V
in
≤
8.5V).
Figure 20
shows the basic configuration for an inverting
regulator. The input voltage is of a positive polarity, but the
output is negative. The output may be less than, equal to, or
greater in magnitude than the input. The relationship be-
tween the magnitude of the input voltage and the output volt-
age is V
o
= V
in
x (t
on
/t
off
).
DS008711-10
FIGURE 20. Basic Inverting Regulator
DS008711-11
V
in
= 5V
V
o
= 15V
V
ripple
= 10 mV
I
o
= 140 mA
f
osc
= 50 kHz
R1 = 140 kΩ
R2 = 10 kΩ
R3 = 0.15Ω
R4 = 200 kΩ
C1 = 1820 pF
C2 = 470 µF
C3 = 20 pF
C4 = 0.0022 µF
L1 = 330 µH
D1 = 1N5818
Figure 21
shows an LM1578A configured as a 5V to −15V
polarity inverter with an output current of 300 mA, a load
regulation of 44 mV (60 mA to 300 mA) and a line regulation
of 50 mV (4.5V
≤
V
in
≤
8.5V).
R1 = (|V
o
| +1) R2 where R2 = 10 kΩ.
R3 = V/(I
L(max, DC)
+ 0.5
∆I
L
).
R4 = 10V
BE1
B
f
/(I
L (max, DC)
+ 0.5
∆I
L
)
where:
V, V
BE1
, V
sat
, and B
f
are defined in the “Buck Converter with
Boosted Output Current” section.
∆I
L
= 2(I
LOAD(min)
)(V
in
+|V
o
|)/V
IN
R5 is defined in the “Buck with Boosted Output Current” sec-
tion.
R6 serves the same purpose as R4 in the Boost Regulator
circuit and is typically 220 kΩ.
C1, C3 and C4 are defined in the “Boost Regulator” section.
C2
≥
I
o
|V
o
|/[f
osc
(|V
o
| + V
in
) V
ripple
]
L1 is found as outlined in the section on buck converters, us-
ing the inductance chart of
Figure 16
for the invert configura-
tion and 20% discontinuity.
FIGURE 19. Boost or Step-Up Regulator
R1 = (V
o
− 1) R2 where R2 = 10 kΩ.
R3 = V/(I
L(max, DC)
+ 0.5
∆I
L
)
where:
∆I
L
= 2(I
LOAD(min)
)(V
o
/V
in
)
∆I
L
is 200 mA in this example.
13
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