LNK603-606/613-616
Applications Example
C6
1 nF
R7
100 V 200 Ω
L1
T1
EE16
1.5 mH
5 V, 555 mA
5
3
10
D7
C3
820 pF
1 kV
R2
SS14
R8
470 kΩ
8
1
200 Ω
D1
D2
C7
1N4007 1N4007
DC
Output
680 µF
10 V
R3
RF1
8.2 Ω
2 W
300 Ω
2
4
VR1
2MM5230B-7
4.7 V
C1
4.7 µF
400 V
C2
4.7 µF
400 V
D5
1N4007
AC
Input
NC
D6
LL4148
LinkSwitch-II
R5
U1
13 kΩ
LNK613DG
1%
D
D3
D4
FB
1N4007 1N4007
BP
R4
S
R6
8.87 kΩ
1%
C4
1 µF
25 V
6.2 kΩ C5
10 µF
16 V
PI-5111-050808
Figure 4.
Energy Efficient USB Charger Power Supply (74% Average Efficiency, <30 mW No-load Input Power).
compensation. A 1 mF value selects the standard compensation.
A 10 mF value selects the enhanced compensation. Table 2
shows the amount of compensation for each device and
bypass capacitor value. The LNK60x devices do not provide
cable drop compensation.
Circuit Description
This circuit shown in Figure 4 is configured as a primary-side
regulated flyback power supply utilizing the LNK613DG. With
an average efficiency of 74% and <30 mW no-load input power
this design easily exceeds the most stringent current energy
efficiency requirements.
The optional bias supply formed by D6 and C5 provides the
operating current for U1 via resistor R4. This reduces the
no-load consumption from ~200 mW to <30 mW and also
increases light load efficiency.
Input Filter
AC input power is rectified by diodes D1 through D4. The
rectified DC is filtered by the bulk storage capacitors C1 and
C2. Inductor L1, 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
allow 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. Fusible resistor RF1
provides protection against catastrophic failure. This 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.
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 D5, R2, R3, and C3.
Output Rectification
The secondary of the transformer is rectified by D7, a 1 A, 40 V
Schottky barrier type for higher efficiency, and filtered by C7. If
lower efficiency is acceptable then this can be replaced with a
1 A PN junction diode for lower cost. In this application C7 was
sized to meet the required output voltage ripple specification
without requiring a post LC filter. To meet battery self discharge
requirement the pre-load resistor has been replaced with a
series resistor and Zener network (R8 and VR1). However in
designs where this is not a requirement a standard 1 kW
resistor can be used.
LNK 613 Primary
The LNK613DG device (U1) incorporates the power switching
device, oscillator, CC/CV control engine, startup, and protection
functions. The integrated 700 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 C4. For the LNK61X devices, the bypass capacitor
value also selects the amount of output cable voltage drop
Output Regulation
The LNK613 regulates the output using ON/OFF control in the
constant voltage (CV) regulation region of the output character-
4
Rev. F 01/10
www.powerint.com
POWERINT [ Power Integrations ]
