Datasheet

LM2588
www.ti.com SNVS117D –APRIL 1998–REVISED APRIL 2013
Figure 57. Boost Regulator
Figure 58. Flyback Regulator
FLYBACK REGULATOR INPUT CAPACITORS
A flyback regulator draws discontinuous pulses of current from the input supply. Therefore, there are two input
capacitors needed in a flyback regulator—one for energy storage and one for filtering (see Figure 58). Both are
required due to the inherent operation of a flyback regulator. To keep a stable or constant voltage supply to the
LM2588, a storage capacitor (≥100 μF) is required. If the input source is a recitified DC supply and/or the
application has a wide temperature range, the required rms current rating of the capacitor might be very large.
This means a larger value of capacitance or a higher voltage rating will be needed for the input capacitor. The
storage capacitor will also attenuate noise which may interfere with other circuits connected to the same input
supply voltage.
In addition, a small bypass capacitor is required due to the noise generated by the input current pulses. To
eliminate the noise, insert a 1.0 μF ceramic capacitor between V
IN
and ground as close as possible to the device.
SWITCH VOLTAGE LIMITS
In a flyback regulator, the maximum steady-state voltage appearing at the switch, when it is off, is set by the
transformer turns ratio, N, the output voltage, V
OUT
, and the maximum input voltage, V
IN
(Max):
V
SW(OFF)
= V
IN
(Max) + (V
OUT
+V
F
)/N (3)
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