NCP1651DR2 ,Single Stage Power Factor Controller2D11N4006D9T3BAS19LT1F1L2D22 D131 71N4006AZ23C18D7 D12100 H1N4006D3L31N4006253010100 HD4 1.5kE25C ..
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NCP1653DR2 , Compact, Fixed−Frequency, Continuous Conduction Mode PFC Controller
NCP1653DR2G , Compact, Fixed−Frequency, Continuous Conduction Mode PFC Controller
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NCP1651DR2
Single Stage Power Factor Controller
AND8124/D
90 W, Universal Input,
Single Stage, PFC
Converter
General DescriptionThis application note describes the implementation of a
90 W, universal input Flyback Power−Factor−Correction
(PFC) converter using On Semiconductor’s NCP1651
controller.
The NCP1651 enables a low cost single−stage (with a low
voltage isolated output) PFC converter as demonstrated in
this application circuit, which is designed for 48 Vdc, at
1.9 A of output current. The NCP1651 is designed to operate
in the fixed frequency, continuous mode (CCM), or
discontinuous (DCM) mode of operation, in a Flyback
converter topology. The converter described in this
application note has the following valuable features:
Features Wide Input V oltage Range (85 − 265 Vac) Galvanic Isolation Primary Side Cycle−by−Cycle and Average Current
Limit Secondary Side Power Limiting High Voltage Start−up Circuit
Detailed Circuit DescriptionOperational description and design equations are
contained in the NCP1651 Data Sheet. This application note
addresses specific design issues related to this converter
design. Please refer to Figure 2 for component reference
designators.
Voltage Regulation LoopWith a Flyback topology, the output is isolated from the
input by the power transformer. Output voltage regulation
can be accomplished in two ways. The first, and the simplest
method is by sensing the primary side voltage of the
auxiliary winding. This eliminates the feedback isolation
circuitry, at the expense of accuracy of voltage regulation
and current sensing. The second method is to sense the
secondary side voltage which is more complex, but provides
better voltage regulation and transient response.
The NCP1651 demo board uses a quad operational
amplifier on the secondary to perform multiple functions.
One section of the amplifier is used as the error amplifier. A
voltage divider comprised of R23, R24, R25 and R33 senses
the output voltage and divides it down to 2.5 V . This signal
is applied to the negative input of the error amplifier; the
2.5 V reference is applied to the non−inverting input of the
error amplifier.
The output of the error amplifier provides a current sink
that drives the LED of the optocoupler. The primary side
optocoupler circuit sinks current from pin 8. This varies the
voltage into the V oltage−to−Current converter that feeds the
reference multiplier.
The loop operation is as follows: If the output voltage is
less than its nominal value, the voltage at the output of the
voltage divider (inverting input to the error amplifier) will
be less than the reference signal at the non−inverting error
amplifier input. This will cause the output of the error
amplifier to increase. The increase in the output of the error
amplifier will cause the optocoupler LED to conduct less
current, which in turn will reduce the current in the
optocoupler photo−transistor. This will increase the voltage
at pin 8 of the chip, and in turn increase the output of the
reference multiplier, causing an increase in the NCP1651
duty cycle.
The current shaping network is comprised of the ac error
amplifier, buffer and current sense amplifier. This network
will force the average input current to maintain a scaled
replica of the current reference on pin 10. The increase of the
reference voltage will cause the current shaping network to
draw more input current, which translates into an increase in
output current as it passes through the transformer. The
increase in current will increase the output power and
therefore, the output voltage. To calculate the loop stability,
it is recommended that the On Semiconductor spread sheet
be used. This is an easy and convenient way to check the gain
and phase of the control loop.
