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PDF AND8262D Data sheet ( Hoja de datos )
| Número de pieza | AND8262D | |
| Descripción | 8W DVD Power Supply | |
| Fabricantes | ON Semiconductor | |
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Hay una vista previa y un enlace de descarga de AND8262D (archivo pdf) en la parte inferior de esta página. Total 9 Páginas | ||
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AND8262/D
8 W DVD Power Supply with
NCP1027
Prepared by: Christophe Basso
ON Semiconductor
Overview
Digital Video Disks players require a few different
voltages to power the logic circuitry but also all
servo−mechanisms linked to the tray and optical head
actuators. The NCP1027 lends itself very well to this kind of
applications where simple architectures lead to the lowest
assembly cost. Despite the variety of low−end DVD players
on the market, there is a common trend on the power supply
requirements:
• Universal input voltage: 85 to 265 Vac, 2 wire power
cord
• 5 different dc voltages, 1 non−filtered bias level:
1. 5 V / 1 A
2. 3.3 V / 1 A
3. – 12 V / 20 mA
4. + 12 V / 20 mA
5. – 23 V / 10 mA
6. Floating display bias
• Low standby power in no−load and partial load
conditions
These specifications can fluctuate depending on a
particular type of player but the basic power supply
architecture remains the same. We will use a current−mode
flyback regulator built around the integrated power
switcher, the NCP1027. This DIP 8 package hosts a high
performance controller together with a low RDS(on) 700 V
BVdss MOSFET. On top of the standby needs, we have
packed other interesting goodies in this circuit. They are
summarized below:
• Brown−out Detection: the controller will not allow
operation in low mains conditions. You can adjust the
level at which the circuit starts or stops operation.
• Ramp Compensation: designing in Continuous
Conduction Mode helps to reduce conduction losses.
However, at low input voltage (85 Vac), the duty−cycle
might exceed 50% and the risk exists to enter a
subharmonic mode. A simple resistor to ground injects
the right compensation level.
• Over Power Protection: a resistive network to the bulk
reduces the peak current capability and accordingly
harnesses the maximum power at high line. As this is
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APPLICATION NOTE
done independently from the auxiliary VCC, the design
gains in simplicity and execution speed.
• Latch−off Input: some manufacturers require a complete
latch−off in presence of an external event, e.g. over
temperature or a severe over−voltage protection. The
controller offers this possibility via a dedicated input.
• Frequency Dithering: the switching frequency (here
65 kHz) is modulated during operation. This naturally
spreads the harmonic content and reduces the peak
value when analyzing the signature.
Design Description
Figure 2 shows the electrical schematic used for this
application. The NCP1027 directly connects to the power
transformer and a classical RCD clamping network prevents
any BVdss runaways. A string of resistors (R14, R15 and R9)
set the minimum operating voltage to increase safety in case
of a low input level: the circuit does not switch until enough
voltage appears on the mains connector. During this time,
VCC goes up and down via the activated high−voltage
current source and self−supplies the controller. When the
mains reaches the adequate level (70 Vac here), the power
supply automatically resumes operation and performs its
duty. Please note that bringing pin 3 above a certain level
(3.5 V) permanently latches off the switcher. It can be useful
in case safety specifications impose a complete shutdown in
presence of a stringent event: Over Temperature Protection
(OTP), latched OverVoltage Protection (OVP)…
As this design enters the Continuous Conduction Mode
(CCM) at low line, we have added some ramp compensation
via a single resistor connected from pin 2 to ground: no
sub−harmonic oscillations can be detected at low line input
and full load.
Thanks to the NCP1027, the power supply is inherently
protected against short−circuits, whatever the VCC pin level
is. An internal circuitry permanently monitors the feedback
pin and starts a timer when pin 4 goes high (open−loop
conditions in startup sequence or in a short−circuit
condition). If the timer reaches completion before the fault
has gone, the switcher stops all pulses and enters an
auto−recovery protective mode. When the fault disappears,
© Semiconductor Components Industries, LLC, 2006
August, 2006 − Rev. 0
1
Publication Order Number:
AND8262/D
1 page  
AND8262/D
Operating Waveforms and Test Results
To perform some tests, we have loaded the prototype converter with a DVD player and artificially loaded some of its outputs,
mainly the +3.3 V and the +5 V. The static board load is the following:
3.3 V = 700 mA
5 V = 500 mA
12 V = 20 mA
–12 V = 25 mA
– 23 V = 2 mA
A 520 mA peak current was then added on top of the 5 V or the 3.3 V output. Results are displayed below:
520 mA
3.3 V
5V
Figure 4. Both Input Levels Give the Same Performance when the 5 V is
Loaded by 520 mA Peaks.
520 mA
3.3 V
5V
Figure 5. Here, the 3 V is Loaded by 520 mA Peaks on Top of
its Current Consumption
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5
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet AND8262D.PDF ] | |
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