LNK623-626
Applications Example
L1
T1
3.5 × 7.6 mm
Ferrite Bead
D8
EEL19
UF4003
12 V, 0.1 A
1
3
6
7
C9
R8
47 MF
R1
24 k7
25 V
5.1 k7
L3
10 MH
1/8 W
D1
FR106
D2
FR106
C3
820 pF
1 kV
1/8 W
D7 SB540
5 V, 1.7 A
R7
11
C8
C10
470 MF
10 V
VR1
1N5272B
510 7
1000 MF
C13
270 pF
R10
47 7
1/8 W
RTN
10 V
8,9,10
C11
R9
47 MF
39 k7
R2
50 V
1/8 W
12
5
F1
3.15 A
390 7
L
D9
UF4003
-22 V, 15 mA
D5
1N4007
C1
C2
85 - 265
VAC
22 MF
22 MF
D6
1N4148
400 V
400 V
4
2
N
RV1
RT1
10 7
275 V
R3
6.34 k7
1%
LinkSwitch-CV
U1
LNK626PG
D3
1N4007
D4
1N4007
D
FB
BP
R5
R4
6.2 k7
S
47 k7
1/8 W
R6
4.02 k7
1%
C6
10 MF
C4
C5
680 pF
50 V
50 V
1 MF
L2
680 uH
50 V
PI-5205-102208
Figure 4. 7 W (10 W peak) Multiple Output Flyback Converter for DVD Applications with Primary Sensed Feedback.
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 can be
completely self-powered from the BYPASS pin and decoupling
capacitor C4. In this design a bias circuit (D6, C6 and R4) was
added to reduce no load input power below ±40 mW.
Circuit Description
This circuit is configured as a three output, primary-side
regulated flyback power supply utilizing the LNK626PG. It can
deliver 7 W continuously and ±0 W peak (thermally limited) from
an universal input voltage range (81 – 261 VAC). Efficiency is
>675 at ±±1 VAC/230 VAC and no-load input power is
<±40 mW at 230 VAC.
The rectified and filtered input voltage is applied to one side of
the primary winding of T±. The other side of the transformer’s
primary winding is driven by the integrated MOSFET in U±. The
leakage inductance drain voltage spike is limited by the clamp
circuit D1, R±, R2, C3 and VR±. The zener bleed clamp
arrangement was selected for lowest no-load input power but in
applications where higher no-load input power is acceptable
VR± may be omitted and the value of R± increased to form a
standard RCD clamp.
Input Filter
AC input power is rectified by diodes D± through D4. The
rectified DC is filtered by the bulk storage capacitors C± and
C2. Inductor L±, L2, C± 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
EN11022 class B with good margin without requiring a
Y capacitor. Fuse F± provides protection against catastrophic
failure. Negative temperature coefficient thermistor RT± limits
the inrush current when AC is first applied to below the
maximum rating of diodes D± through D4. Metal oxide varistor
RV± clamps the AC input during differential line transients,
protecting the input components and maintaining the peak
drain voltage of U± below its 700 V BVDSS rating. For differential
surge levels at or below 2 kV this component may be omitted.
Output Rectification
The secondaries of the transformer are rectified by D7, D8 and
D9. A Schottky barrier type was used for the main 1 V output
for higher efficiency. The +±2 V and -22 V outputs use an
ultrafast rectifier diode. The main output is post filtered by L3
and C±0 to remove switching frequency ripple. Resistors R7,
R8 and R9 provide a preload to maintain the output voltages
within their respective limits when unloaded. To reduce high
frequency ringing and associated radiated EMI an RC snubber
formed by R±0 and C±3 was added across D7.
LNK626 Primary
The LNK626PG device (U±) incorporates the power switching
device, oscillator, CV control engine, startup, and protection
4
Rev. E 09/09
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