LNK520GN Power Integrations, LNK520GN Datasheet - Page 4

IC SWIT OCP CV/CC HV 8SMD

LNK520GN

Manufacturer Part Number
LNK520GN
Description
IC SWIT OCP CV/CC HV 8SMD
Manufacturer
Power Integrations
Series
LinkSwitch®r
Datasheet

Specifications of LNK520GN

Output Isolation
Isolated
Frequency Range
24 ~ 49.5kHz
Voltage - Output
700V
Power (watts)
5.50W
Operating Temperature
-40°C ~ 150°C
Package / Case
8-SMD Gull Wing, 7 Leads
Output Voltage
5.6 V
Input / Supply Voltage (max)
265 VAC
Input / Supply Voltage (min)
85 VAC
Duty Cycle (max)
80 %
Switching Frequency
42 KHz
Supply Current
0.75 mA
Operating Temperature Range
- 40 C to + 150 C
Mounting Style
SMD/SMT
For Use With
596-1006 - KIT DESIGN ACCELERATOR ADAPTER
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

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The characteristics described above provide an approximate
CV/CC power supply output without the need for secondary side
voltage or current feedback. The output voltage regulation is
influenced by how well the voltage across C2 tracks the reflected
output voltage. This tracking is influenced by the coupling
between transformer output and bias windings. Tight coupling
improves CV regulation and requires only a low value for resistor
R2. Poor coupling degrades CV regulation and requires a higher
value for R2 to filter leakage inductance spikes on the bias
winding voltage waveform. This circuitry, used with standard
transformer construction techniques, provides much better
output load regulation than a linear transformer, making this an
ideal power supply solution in many low power applications.
If even tighter load regulation is required, an optocoupler
configuration can be used while still employing the constant
output current characteristics provided by LinkSwitch.
Optional Secondary Feedback
Figure 6 shows a typical power supply schematic outline using
LinkSwitch with optocoupler feedback to improve output voltage
regulation. On the primary side, the schematic only differs
from Figure 5 by the addition of optocoupler U1 transistor in
parallel to R1.
On the secondary side, the addition of voltage sense circuit
components R4, VR1 and U1 LED provide the voltage feedback
signal. In the example shown, a simple Zener (VR1) reference
is used though more accurate references may be employed for
improved output voltage tolerancing and to provide cable drop
compensation, if required. Resistor R4 provides biasing for VR1.
The regulated output voltage is equal to the sum of the VR1
Zener voltage plus the forward voltage drop of the U1 LED.
Resistor R5 is an optional low value resistor to limit U1 LED
peak current due to output ripple. Manufacturerʼs specifications
Figure 6. Power Supply Schematic Outline with Optocoupler Feedback, Providing Tight CV Regulation.
4
LNK520
E
2/05
85-265
VAC
LinkSwitch
LNK520
R3
D
S
for U1 current and VR1 slope resistance should be consulted
to determine whether R5 is required.
When the power supply operates in the constant current (CC)
region, for example at start up and when charging a battery,
the output voltage is below the voltage feedback threshold
defined by U1 and VR1 and the optocoupler is fully off. In this
region, the circuit behaves exactly as previously described with
reference to Figure 5 where the voltage across C2 and therefore
the current flowing through R1 increases with increasing output
voltage and the LinkSwitch internal current limit is adjusted to
provide an approximate CC output characteristic.
When the output reaches the voltage feedback threshold set by
U1 and VR1, the optocoupler turns on. Any further increase
in the power supply output voltage results in the U1 transistor
current increasing. The resulting increase in the LinkSwitch
CONTROL current reduces the duty cycle according to
Figure 4 and therefore, maintains the output voltage
regulation.
Figure 7 shows the influence of optocoupler feedback on the
output characteristic. The envelope defined by the dashed lines
represent the worst-case power supply DC output voltage and
current tolerances (unit-to-unit and over the input voltage range)
if an optocoupler is not used. A typical example of an inherent
(without optocoupler) output characteristic is shown dotted.
This is the characteristic that would result if U1, R4, R5 and
VR1 were removed. The optocoupler feedback results in the
characteristic shown by the solid line. The load variation arrow in
Figure 7 represents the locus of the output characteristic normally
seen during a battery charging cycle. The two characteristics
are identical as the output voltage rises but then separate as
shown when the voltage feedback threshold is reached. This
C
C3
D3
C1
T1
D1
D2
R1
C2
R2
C4
VR1
U1
R5
R4
V
RTN
OUT
PI-3703-030404

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