LNK6427 データシートの表示（PDF） - Unspecified
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LNK6427 Datasheet PDF : 18 Pages
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LNK64x4-64x8
Applications Example
Circuit Description
This circuit shown in Figure 4 is configured as a primary-side
regulated flyback power supply utilizing the LNK6448K. With an
average efficiency of 78% and <30 mW no-load input power this
design easily exceeds the most stringent current energy efficiency
requirements.
Input Filter
AC input power is rectified by bridge BR1. The rectified DC is filtered
by the bulk storage capacitors C1 and C2. Inductors L2 and L3,
together with C1 and C2 form a pi (π) filter, which attenuates
conducted differential-mode EMI noise. This configuration along with
Power Integrations transformer E-Shield™ technology allows this
design to meet EMI standard EN55022 class B with good margin
without requiring a Y capacitor, even with the output connected to
safety earth ground. A ferrite bead for L3 is sufficient especially
when the output of the supply is floating. Fuse F1 provides protection
against catastrophic failure. NTC (Negative Thermal Coefficient)
thermistor RT1 is used to limit the rush current to below the peak
specification of BR1 during start-up especially at high-line input
voltage. High-line results in the highest current into C1 and C2. F1
and RT1 can be replaced by a single fusible resistor. If the reduction
in efficiency is acceptable, a bridge with a higher IFSM rating may also
allow removal of RT1. If a fusible resistor is selected, use a
flameproof type. It should be suitably rated (typically a wire wound
type) to withstand the instantaneous dissipation while the input
capacitors charge when first connected to the AC line.
LNK6448K Primary
The LNK6448K device (U1) incorporates the power switching device,
oscillator, CC/CV control engine, start-up, and protection functions.
The integrated 725 V MOSFET provides a large drain voltage margin
in universal input AC applications, increasing reliability and also
reducing the output diode voltage stress by allowing a greater
transformer turns ratio. The device is completely self-powered from
the BYPASS pin and decoupling capacitor C7. For the LNK64xx
devices, there are 4 options for different amount of cable drop
compensation determined by the third digit in the device part
number. Table 2 shows the amount of compensation for each device.
The LNK644x devices do not provide cable drop compensation.
The optional bias supply formed by D3 and C8 provides the operating
current for U1 via resistor R8. This reduces the no-load consumption
from ~200 mW to <30 mW and also increases light load efficiency.
The rectified and filtered input voltage is applied to one side of the
primary winding of T1. The other side of the transformer’s primary
winding is driven by the integrated MOSFET in U1. The leakage
inductance drain voltage spike is limited by an RCD-R clamp
consisting of D2, R3, R11, and C6.
Output Rectification
The secondary of the transformer is rectified by D1, a 10 A, 45 V
Schottky barrier type for higher efficiency, and filtered by C3, L1 and
C4. If lower efficiency is acceptable then this can be replaced with a
5 A PN junction diode for lower cost. In this application C3 and C4
are sized to meet the required output voltage ripple specification with
a ferrite bead L1, which eliminates the high switching noise on the
output. A pre-load resistor R2 is used to meet the regulation
specification. If the battery self-discharge is required, the pre-load
resistor can be replaced with a series resistor and Zener network.
Output Regulation
The LNK64xx family of devices regulates the output using ON/OFF
control in the constant voltage (CV) regulation region of the output
characteristic and frequency control for constant current (CC)
regulation. The feedback resistors (R6 and R7) were selected using
standard 1% resistor values to center both the nominal output
voltage and constant current regulation thresholds.
BR1
B10S-G
1000 V
F1
1A
RT1
10 Ω
tO
90 - 265
VAC
L
N
TP1
TP2
R10
4.7 kΩ
L2
1 mH
C1
10 µF
400 V
L3
Ferrite Bead
(3.5 × 7.6 mm)
C5
R1 1 nF
10 Ω 50 V
R11
200 kΩ
T1
EPC17
5
FL1
L1
Ferrite Bead
(3.5 × 7.6 mm)
5 V, 2 A
C6
470 pF
250 V
6
D1
SBR1045SP5-13
C3
680 µF
10 V
FL2
C4
680 µF
10 V
R2
2.55 kΩ
1%
J1-1
RTN
4
R3
150 Ω
J1-4
6.0
3
D2
S1ML
5.0
C2
15 µF
400 V
R5
R6
2.4 Ω
4.0
44.2 kΩ
LinkSwitch-3 1%
3.0
U1
D3
LNK6448K
D
RS1ML
2.0
FB
115 VAC
230 VAC
BP
S
C7
1 µF
50 V
R7
10 kΩ
1%
R8
2.37 kΩ
1%
C8
10 µF
25 V
PI-7209-020515
1.0
0.0
0 0.5 1 1.5 2 2.5 3
Output Current (A)
Figure 4. Energy Efficient USB Charger Power Supply (78% Average Efficiency, <30 mW No-load Input Power).
4
Rev. C 03/16
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