LNK623-626
Applications Example
L1
3.5 × 7.6 mm
Ferrite Bead
1
R1
5.1 k
1/8 W
VR1
1N5272B
T1
EEL19
6
D8
UF4003
C9
47 F
25 V
D7 SB540
R8
24 k
1/8 W
12 V, 0.1 A
3
C3
820 pF
1 kV
7
D1
FR106
D2
FR106
L3
10 H
C10
470 F
10 V
R9
39 k
1/8 W
5 V, 1.7 A
R7
510
1/8 W
RTN
11
8,9,10
R10
47
C13
270 pF
C8
1000 F
10 V
C11
47 F
50 V
L
85
- 265
VAC
N
F1
3.15 A
C1
22 F
400 V
RT1
10
RV1
275 V
C2
22 F
400 V
R2
390
D5
1N4007
12
5
D9
UF4003
D6
1N4148
4
-22 V, 15 mA
2
D3
1N4007
D4
1N4007
D
LinkSwitch-CV
U1
LNK626PG
FB
BP
R3
6.34 k
1%
S
R4
6.2 k
C4
1 F
50 V
L2
680 uH
R5
47 k
1/8 W
R6
4.02 k
C5
1%
680 pF
50 V
C6
10 F
50 V
PI-5205-102208
Figure 4.
7 W (10 W peak) Multiple Output Flyback Converter for DVD Applications with Primary Sensed Feedback.
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 10 W peak (thermally limited) from
an universal input voltage range (85 – 265 VAC). Efficiency is
>67% at 115 VAC/230 VAC and no-load input power is
<140 mW at 230 VAC.
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, L2, 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. Fuse F1 provides protection against catastrophic
failure. Negative temperature coefficient thermistor RT1 limits
the inrush current when AC is first applied to below the
maximum rating of diodes D1 through D4. Metal oxide varistor
RV1 clamps the AC input during differential line transients,
protecting the input components and maintaining the peak
drain voltage of U1 below its 700 V BV
DSS
rating. For differential
surge levels at or below 2 kV this component may be omitted.
LNK626 Primary
The LNK626PG device (U1) incorporates the power switching
device, oscillator, 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 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 140 mW.
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 the clamp
circuit D5, R1, R2, C3 and VR1. The zener bleed clamp
arrangement was selected for lowest no-load input power but in
applications where higher no-load input power is acceptable
VR1 may be omitted and the value of R1 increased to form a
standard RCD clamp.
Output Rectification
The secondaries of the transformer are rectified by D7, D8 and
D9. A Schottky barrier type was used for the main 5 V output
for higher efficiency. The +12 V and -22 V outputs use an
ultrafast rectifier diode. The main output is post filtered by L3
and C10 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 R10 and C13 was added across D7.
4
Rev. E 09/09
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