R4, C3 and C4 are necessary for continuous operation and
are typically 220 kΩ, 20 pF, and 0.0022 µF respectively.
Typical Applications (Continued)
C1 is the timing capacitor found in Figure 1.
C2 ≥ Io (Vo − Vin)/(fosc Vo Vripple).
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 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-
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 ≤
Vin ≤ 8.5V).
=
age is Vo Vin x (ton/toff).
DS008711-10
FIGURE 20. Basic Inverting Regulator
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 ≤ Vin ≤ 8.5V).
DS008711-11
=
=
R4 200 kΩ
Vin 5V
=
=
R1 (|Vo| +1) R2 where R2 10 kΩ.
=
=
C1 1820 pF
Vo 15V
=
R3 V/(IL(max, DC) + 0.5 ∆IL).
=
=
C2 470 µF
Vripple 10 mV
=
R4 10VBE1Bf/(IL (max, DC) + 0.5 ∆IL)
=
=
C3 20 pF
Io 140 mA
where:
=
=
C4 0.0022 µF
fosc 50 kHz
V, VBE1, Vsat, and Bf are defined in the “Buck Converter with
Boosted Output Current” section.
=
=
L1 330 µH
R1 140 kΩ
=
=
D1 1N5818
R2 10 kΩ
=
∆IL 2(ILOAD(min))(Vin +|Vo|)/VIN
=
R3 0.15Ω
R5 is defined in the “Buck with Boosted Output Current” sec-
tion.
FIGURE 19. Boost or Step-Up Regulator
R6 serves the same purpose as R4 in the Boost Regulator
circuit and is typically 220 kΩ.
=
=
R1 (Vo − 1) R2 where R2 10 kΩ.
=
R3 V/(IL(max, DC) + 0.5 ∆IL)
C1, C3 and C4 are defined in the “Boost Regulator” section.
where:
C2 ≥ Io |Vo|/[fosc(|Vo| + Vin) Vripple
]
=
∆IL 2(ILOAD(min))(Vo/Vin
)
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.
∆IL is 200 mA in this example.
13
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