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LM3524D Datasheet - Page 16

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Typical Applications
(Continued)
To apply the above theory a complete step-up switching
regulator is shown in Figure 20 Since V
is 5V V
IN
to V
The input voltage is divided by 2 to bias the error
IN
amplifier’s inverting input The output voltage is
R2
V
1
V
2 5
e
a
c
e
c
OUT
INV
R1
The network D1 C1 forms a slow start circuit
This holds the output of the error amplifier initially low thus
reducing the duty-cycle to a minimum Without the slow start
L1
25 turns No 24 wire on Ferroxcube No K300502 Torroid core
e
l
FIGURE 20 15V 0 5A Step-Up Switching Regulator
FIGURE 21
circuit the inductor may saturate at turn-on because it has to
is tied
supply high peak currents to charge the output capacitor
REF
from 0V It should also be noted that this circuit has no
supply rejection By adding a reference voltage at the non-
inverting input to the error amplifier see Figure 21 the input
R2
1
a
voltage variations are rejected
R1
The LM3524D can also be used in inductorless switching
regulators Figure 22 shows a polarity inverter which if con-
nected to Figure 20 provides a
FIGURE 22
TL H 8650 – 26
16
15V unregulated output
b
TL H 8650– 25
TL H 8650– 27

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