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

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.

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

DS012420-49

FIGURE 33. 12V Boost Regulator

DS012420-62

A: Switch Voltage,10V/div

B: Switch Current, 5A/div

C: Inductor Current, 5A/div

D: Output Ripple Voltage,

100 mV/div, AC-Coupled

FIGURE 34. Switching Waveforms

DS012420-63

FIGURE 35. V

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