LNK501PN Power Integrations, LNK501PN Datasheet - Page 6

• Manufacturer Part Number: LNK501PN
• Description: IC SWIT OCP CV/CC HV 8DIP
• Manufacturer: Power Integrations
• Series: LinkSwitch®r

Specifications of LNK501PN

• Output Isolation: Isolated
• Frequency Range: 26 ~ 46kHz
• Voltage - Output: 700V
• Power (watts): 4W
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 8-DIP (0.300", 7.62mm), 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: 1.06 mA
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: Through Hole
• For Use With: 596-1001 - KIT DESIGN ACCELERATOR ADAPTER
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 596-1031-5

However, in laboratory bench tests, it is often more convenient
to test the power supply output characteristic starting from a
low output current and gradually increasing the load. In this
case, the optocoupler feedback regulates the output voltage until
the peak output power curve is reached as shown in Figure 8.
Under these conditions, the output current will continue to rise
until the peak power point is reached and the optocoupler turns
off. Once the optocoupler is off, the CONTROL pin feedback
current is determined only by R1 and R3 and the output current
therefore folds back to the inherent CC characteristic as shown.
Since this type of load transition does not normally occur in a
battery charger, the output current never overshoots the inherent
constant current value in the actual application.
In some applications it may be necessary to avoid any output
current overshoot, independent of the direction of load variation.
To achieve this goal, the minimum voltage feedback threshold
should be set at V
CC to CV transition point of the inherent characteristic will
always occur below the voltage feedback threshold. However, the
output voltage tolerance is then increased, since the inherent CV
characteristic tolerance below V
of the optocoupler feedback circuit.
Applications Example
The circuit shown in Figure 9 shows a typical implementation
of an approximate constant voltage / constant current (CV/CC)
charger using LinkSwitch. This design delivers 2.75 W with
a nominal peak power point voltage of 5.5 V and a current of
500 mA. Efficiency is greater than 70% over an input range
of 85 VAC to 265 VAC.
The bridge rectifier, BR1, rectifies the AC input. Resistor RF1
is a fusible type providing protection from primary side short
circuits. The rectified AC is smoothed by C1 and C2 with
inductor L1 forming a pi-filter in conjunction with C1 and C2
to filter conducted EMI. The switching frequency of 42 kHz
allows such a simple EMI filter to be used without the need for
a Y capacitor while still meeting international EMI standards.
When power is applied, high voltage DC appears at the DRAIN
pin of LinkSwitch (U1). The CONTROL pin capacitor C3 is
then charged through a switched high voltage current source
connected internally between the DRAIN and CONTROL pins.
When the CONTROL pin reaches approximately 5.6 V relative
to the SOURCE pin, the internal current source is turned off. The
internal control circuitry is activated and the high voltage MOSFET
starts to switch, using the energy in C3 to power the IC.
When the MOSFET is on, the high voltage DC bus is connected
to one end of the transformer primary, the other end being
connected to primary return. As the current ramps in the
primary of flyback transformer T1, energy is stored. This
energy is delivered to the output when the MOSFET turns off
each switching cycle.
6
LNK501
I
2/05
O(MAX)
. This will ensure that the voltage at the
O(MAX)
is added to the tolerance
The secondary of the transformer is rectified and filtered by D6
and C5 to provide the DC output to the load.
LinkSwitch dramatically simplifies the secondary side by
controlling both the constant voltage and constant current regions
entirely from the primary side. This is achieved by monitoring
the primary-side V
Diode D5 and capacitor C4 form the primary clamp network.
This both limits the peak drain voltage due to leakage inductance
and provides a voltage across C4, which is equal to the V
an error due to the parasitic leakage inductance. Resistor R2
filters the leakage inductance spike and reduces the error in the
value of the V
that is fed into the CONTROL pin to regulate the output.
During CV operation the output is regulated through control of
the duty cycle. As the current into the CONTROL pin exceeds
approximately 2 mA, the duty cycle begins to reduce, reaching
30% at a CONTROL pin current of 2.3 mA.
Under light or no-load conditions, when the duty cycle reaches
approximately 4%, the switching frequency is reduced to lower
energy consumption.
If the output load is increased beyond the peak power point
(defined by 0.5·L
The reduced CONTROL pin current will lower the internal
LinkSwitch current limit (current limit control) providing an
approximately constant current output characteristic. If the
load is increased and the CONTROL pin current falls below
approximately 1 mA, the CONTROL pin capacitor C3 will
discharge and the supply enters auto-restart.
Current limit control removes the need for any secondary side
current sensing components (sense resistor, transistor, opto
coupler and associated components). Removing the secondary
sense circuit dramatically improves efficiency, giving the
associated benefit of reduced enclosure size.
Key Application Considerations
Design Output Power
Table 1 (front page) shows the maximum continuous output
power that can be obtained under the following conditions:
1. The minimum DC input bus voltage is 90 V or higher.
2. Design is a discontinuous mode flyback converter, with
This corresponds to a filter capacitor of 3 µF/W for
universal input and 1 µF/W for 230 VAC or 115 VAC
input with doubler input stage.
nominal primary inductance value and a V
40 V to 60 V. Continuous mode designs can result in loop
instability and are therefore not recommended.
OR
. Resistor R1 converts this voltage into a current
P
·I
OR
LIM
(voltage output reflected).
2
·f), the output voltage and V
OR
in the range
OR
OR
falls.
plus