LM2587EVAL National Semiconductor, LM2587EVAL Datasheet - Page 10

• Manufacturer Part Number: LM2587EVAL
• Description: EVALUATION BOARD FOR LM2587
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r

Specifications of LM2587EVAL

• Main Purpose: DC/DC, Step Up
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 12V
• Current - Output: 1A
• Voltage - Input: 4 ~ 40V
• Regulator Topology: Boost
• Frequency - Switching: 100kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM2587
• For Use With: 551011367-061 - BOARD WEBENCH LM2577,LM2585/87
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: *LM2587EVAL

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Flyback Regulator Operation
The LM2587 is ideally suited for use in the flyback regulator
topology. The flyback regulator can produce a single output
voltage, such as the one shown in
voltages. In
put voltage that is inside the range of the input voltage. This
feature is unique to flyback regulators and cannot be dupli-
cated with buck or boost regulators.
The operation of a flyback regulator is as follows (refer to
Figure
primary winding of the transformer, T1, storing energy in the
magnetic field of the transformer. Note that the primary and
secondary windings are out of phase, so no current flows
through the secondary when current flows through the prima-
As shown in
regulator are shown in
4): when the switch is on, current flows through the
Figure
Figure
4, the LM2587 can be used as a flyback regulator by using a minimum number of external components. The switching waveforms of this
Figure
4, the flyback regulator generates an out-
5. Typical Performance Characteristics observed during the operation of this circuit are shown in
Figure
FIGURE 4. 12V Flyback Regulator Design Example
4, or multiple output
10
ry. When the switch turns off, the magnetic field collapses,
reversing the voltage polarity of the primary and secondary
windings. Now rectifier D1 is forward biased and current flows
through it, releasing the energy stored in the transformer. This
produces voltage at the output.
The output voltage is controlled by modulating the peak
switch current. This is done by feeding back a portion of the
output voltage to the error amp, which amplifies the difference
between the feedback voltage and a 1.230V reference. The
error amp output voltage is compared to a ramp voltage pro-
portional to the switch current (i.e., inductor current during the
switch on time). The comparator terminates the switch on time
when the two voltages are equal, thereby controlling the peak
switch current to maintain a constant output voltage.
1231610
Figure
6.