LM2585S-12 National Semiconductor, LM2585S-12 Datasheet - Page 11

DC/DC Converter IC

LM2585S-12

Manufacturer Part Number
LM2585S-12
Description
DC/DC Converter IC
Manufacturer
National Semiconductor
Datasheets

Specifications of LM2585S-12

Input Voltage
40V
Output Voltage
12V
No. Of Pins
5
Peak Reflow Compatible (260 C)
No
Termination Type
SMD
Supply Voltage Max
40V
Leaded Process Compatible
No
Mounting Type
Through Hole
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LM2585S-12
Manufacturer:
NS/国半
Quantity:
20 000
Flyback Regulator Operation
The LM2585 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 Figure 4, or multiple output
voltages. In Figure 4, the flyback regulator generates an out-
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 4): when the switch is on, current flows through the
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 Figure 4, the LM2585 can be used as a flyback regulator by using a minimum number of external components. The switching waveforms of this
regulator are shown in Figure 5. Typical Performance Characteristics observed during the operation of this circuit are shown in Figure 6.
FIGURE 4. 12V Flyback Regulator Design Example
11
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.
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