LM2588S-3.3 National Semiconductor, LM2588S-3.3 Datasheet - Page 20

• Manufacturer Part Number: LM2588S-3.3
• Description: SIMPLE SWITCHER 5A Flyback Regulator with
• Manufacturer: National Semiconductor

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Step-Up (Boost) Regulator Operation
Figure 33 shows the LM2588 used as a step-up (boost)
regulator. This is a switching regulator that produces an out-
put voltage greater than the input supply voltage.
A brief explanation of how the LM2588 Boost Regulator
works is as follows (refer to Figure 33 ). When the NPN
switch turns on, the inductor current ramps up at the rate of
V
By adding a small number of external components (as shown in Figure 33 ), the LM2588 can be used to produce a regulated out-
put voltage that is greater than the applied input voltage. The switching waveforms observed during the operation of this circuit
are shown in Figure 34 . Typical performance of this regulator is shown in Figure 35 .
Typical Performance Characteristics
A: Switch Voltage,10V/div
B: Switch Current, 5A/div
C: Inductor Current, 5A/div
D: Output Ripple Voltage,
100 mV/div, AC-Coupled
IN
/L, storing energy in the inductor. When the switch turns
FIGURE 34. Switching Waveforms
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FIGURE 33. 12V Boost Regulator
20
off, the lower end of the inductor flies above V
its current through diode (D) into the output capacitor (C
at a rate of (V
tor during the switch on time is transferred to the output dur-
ing the switch off time. The output voltage is controlled by
adjusting the peak switch current, as described in the flyback
regulator section.
FIGURE 35. V
OUT
− V
OUT
IN
Response to Load Current Step
)/L. Thus, energy stored in the induc-
DS012420-49
IN
, discharging
DS012420-63
OUT
)