lm2587sx-5.0 National Semiconductor Corporation, lm2587sx-5.0 Datasheet - Page 19

• Manufacturer Part Number: lm2587sx-5.0
• Description: Simple Switcher 5a Flyback Regulator
• Manufacturer: National Semiconductor Corporation

Step-Up (Boost) Regulator
Operation
Figure 33 shows the LM2587 used as a step-up (boost)
regulator. This is a switching regulator that produces an
output voltage greater than the input supply voltage.
A brief explanation of how the LM2587 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
By adding a small number of external components (as shown in Figure 33), the LM2587 can be used to produce a regulated output 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, 10 V/divB: Switch Current, 5 A/divC: Inductor Current, 5 A/divD: Output Ripple Voltage,
100 mV/div, AC-Coupled
Horizontal: 2 µs/div
FIGURE 34. Switching Waveforms
FIGURE 33. 12V Boost Regulator
19
V
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
inductor during the switch on time is transferred to the output
during the switch off time. The output voltage is controlled by
adjusting the peak switch current, as described in the flyback
regulator section.
IN
/L, storing energy in the inductor. When the switch turns
OUT
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IN
)/L. Thus, energy stored in the
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, discharging
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OUT
)