Datasheet

LM2585
SNVS120F –APRIL 2000–REVISED APRIL 2013 www.ti.com
Step-Up (Boost) Regulator Operation
Figure 45 shows the LM2585 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 LM2585 Boost Regulator works is as follows (refer to Figure 45). When the NPN
switch turns on, the inductor current ramps up at the rate of V
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
− V
IN
)/L. Thus, energy stored in the 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 Flyback Regulator.
Figure 45. 12V Boost Regulator
By adding a small number of external components (as shown in Figure 45), 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 46. Typical performance of this regulator is shown in
Figure 47.
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 46. Switching Waveforms
Figure 47. V
OUT
Response to Load Current Step
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