RDK-201 Power Integrations, RDK-201 Datasheet - Page 7

• Manufacturer Part Number: RDK-201
• Description: KIT REF DESIGN LINKSWITCH-CV
• Manufacturer: Power Integrations
• Series: LinkSwitch®-CVr
• Type: MOSFET & Power Driverr

Specifications of RDK-201

• Main Purpose: AC/DC, Primary Side
• Outputs And Type: 1, Isolated
• Power - Output: 6W
• Voltage - Output: 5V
• Current - Output: 1.2A
• Voltage - Input: 90 ~ 265VAC
• Regulator Topology: Flyback
• Board Type: Fully Populated
• Utilized Ic / Part: LNK626
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: LNK62x
• Other names: 596-1266

11-Nov-08
RDR-201 6 W LinkSwitch-CV Adapter
The clamp circuit formed by resistors R1 and R2 along with blocking diode D5 and
capacitor C3 ensures that the drain node voltage is well below the 700 V rating of the
internal MOSFET of U1. The clamp circuit is also carefully designed to reduce and
dampen any oscillation present in the voltage spike caused by the transformer’s leakage
inductance.
4.4 Output Rectification
The secondary output is rectified by diode D7 which is placed in the return leg to help
reduce EMI and simplify the transformer construction. An RC snubber circuit composed
of resistor R7 and capacitor C6 is placed across the output diode to also reduce high
frequency EMI. A stable output voltage is maintained by capacitor C7.
Inductor L2 and capacitor C8 form an LC post filter which helps to attenuate switching
noise and reduces output ripple. Resistor R8 is a preload resistor whose value has been
empirically chosen to provide the best possible regulation at light loads without
significantly affecting no-load input power or efficiency.
4.5 Feedback Winding
LinkSwitch-CV eliminates the need for an optocoupler for tight output voltage regulation,
as good as ±5 %, through the use of a feedback winding. The feedback (FB) pin voltage,
which is derived from the voltage divider formed by resistors R3 and R4, is sampled
approximately 2.5 µs after U1’s internal MOSFET turns off. Based upon this information
the device regulates the output voltage.
The feedback winding was also designed with more turns than necessary so that it may
act as a bias winding. The winding provides bias current to U1 through the bypass pin
(BP) and reduces the input power consumption during light loads and no-load conditions.
Resistor R6 helps to dampen out any ringing present on the feedback winding and
ensures that the waveform at the FB pin at 2.5 us is free from any ringing. Capacitor C5
provides a stable bias voltage while resistor R5 is chosen to supply the necessary BP pin
current. Capacitor C4 is the BP pin capacitor and should be placed as close as possible
to the BP pin and source pins of the device.
Power Integrations
Tel: [phone] Fax: [phone]
Page 7 of 32
www.powerint.com