Step-Up (Boost) Regulator Operation

Figure 30 shows the LM2585 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 LM2585 Boost Regulator

works is as follows (refer to

Figure 30). 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.

DS012515-48

By adding a small number of external components (as shown in

Figure 30), the LM2585 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 31. Typical performance of this regulator is

shown in

Figure 32.

FIGURE 30. 12V Boost Regulator

DS012515-49

A: Switch Voltage, 10 V/div

B: Switch Current, 2 A/div

C: Inductor Current, 2 A/div

D: Output Ripple Voltage,

100 mV/div, AC-Coupled

Horizontal: 2 µs/div

FIGURE 31. Switching Waveforms

DS012515-50

FIGURE 32. V

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