LM2586 datasheet(18/28 Pages) NSC

18 / 28 page

Typical Flyback Regulator Applications (Continued)

Step-Up (Boost) Regulator Operation

Figure 30 shows the LM2586 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 LM2586 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

IN/L, storing energy in the inductor. When the switch turns

off, the lower end of the inductor flies above V

IN, discharging

its current through diode (D) into the output capacitor (C

OUT)

at a rate of (V

OUT −VIN)/L. Thus, energy stored in the induc-

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 30), the LM2586 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 31. Typical performance of this regulator is shown in Figure 32.

DS012516-47

Top View

FIGURE 27. Schott 26606

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Top View

FIGURE 28. Schott 67140900

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Top View

FIGURE 29. Schott 67140890

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FIGURE 30. 12V Boost Regulator

LM2586 Fiches technique(PDF) 18 Page - National Semiconductor (TI)