LNK562-564
C5
220 µF
25 V
VR1*
D1
1N4937
L1
D4
UF4002
RF1*
R3 1N5240B
T1
EE16
6 V,
3300 µH
8.2 Ω
2 kΩ
10 V
L
0.33 A
2
1
7
6
J-1
J3-2
J3-1
RTN
2.5 W
C1
10 µF
400 V
90-265
VAC
J-2
4
N
D2
1N4005
5
R1
37.4 kΩ
D3
1N4005
C4*
D
S
100 pF
C3
330 nF
50 V
FB
BP
250 VAC
LinkSwitch-LP
U1
R2
3 kΩ
LNK564P
C2
0.1 µF
*Optional components
50 V
PI-4106-101105
Figure 5. 6 V, 330 mA CV/CC Linear Replacement Power Supply.
output of the power supply), the power supply will turn OFF
for 800 ms and then turn back on for 100 ms. It will continue
in this mode until the auto-restart threshold is exceeded. This
function reduces the average output current during an output
short circuit condition.
Applications Example
The circuit shown in Figure 5 is a typical implementation of
a 6 V, 330 mA, constant voltage, constant current (CV/CC)
output power supply.
No-load consumption can be further reduced by increasing C3
to 0.47 µF or higher.
AC input differential filtering is accomplished with the very
low cost inputfilter stage formed by C1 and L1.The proprietary
frequency jitter feature of the LNK564 eliminates the need for
an input pi filter, so only a single bulk capacitor is required.
Adding a sleeve may allow the input inductor L1 to be used as a
fuseaswellasafiltercomponent.ThisverysimpleFilterfuse™
input stage further reduces system cost.Alternatively, a fusible
resistor RF1 may be used to provide the fusing function.
A Clampless primary circuit is achieved due to the very
tight tolerance current limit trimming techniques used in
manufacturing the LNK564, plus the transformer construction
techniques used. Peak drain voltage is therefore limited to
typically less than 550 V at 265 VAC, providing significant
margin to the 700 V minimum drain voltage specification
(BVDSS).
Input diode D2 may be removed from the neutral phase in
applications where decreased EMI margins and/or decreased
input surge withstand is allowed. In such applications, D1 will
need to be an 800 V diode.
Outputrectificationandfilteringisachievedwithoutputrectifier
D4 and filter capacitor C5. Due to the auto-restart feature, the
average short circuit output current is significantly less than
1A,allowinglowcostrectifierD4tobeused.Outputcircuitryis
designedtohandleacontinuousshortcircuitonthepowersupply
output. Diode D4 is an ultra-fast type, selected for optimum
V/I output characteristics. Optional resistor R3 provides a pre-
load, limiting the output voltage level under no-load output
conditions.Despitethispre-load,no-loadconsumptioniswithin
targets at approximately 140 mW at 265 VAC. The additional
margin of no-load consumption requirement can be achieved
by increasing the value of R4 to 2.2 kΩ or higher while still
maintaining output voltage well below the 9 V maximum
specification. Placement is left on the board for an optional
Zener clamp (VR1) to limit maximum output voltage under
open loop conditions, if required.
The power supply utilizes simplified bias winding voltage
feedback, enabled by LNK564 ON/OFF control. The resistor
dividerformedbyR1andR2determinetheoutputvoltageacross
thetransformerbiaswindingduringtheswitchOFFtime. Inthe
V/Iconstantvoltageregion,theLNK564deviceenables/disables
switchingcyclestomaintain1.69VontheFBpin.DiodeD3and
lowcostceramiccapacitorC3providerectificationandfiltering
oftheprimaryfeedbackwindingwaveform.Atincreasedloads,
beyond the constant power threshold, the FB pin voltage begins
to reduce as the power supply output voltage falls. The internal
oscillator frequency is linearly reduced in this region until it
reaches typically 50% of the starting frequency. When the FB
pin voltage drops below the auto-restart threshold (typically
0.8 V on the FB pin, which is equivalent to 1 V to 1.5 V at the
F
10/05
4
POWERINT [ Power Integrations ]
