RDK-251 Power Integrations, RDK-251 Datasheet - Page 11

• Manufacturer Part Number: RDK-251
• Description: KIT REF DESIGN FOR LNK457D
• Manufacturer: Power Integrations
• Series: LinkSwitch®-PLr

Specifications of RDK-251

• Current - Output / Channel: 350mA
• Outputs And Type: 1, Isolated
• Voltage - Output: 12 ~ 18 V
• Features: Dimmable
• Voltage - Input: 90 ~ 265VAC
• Utilized Ic / Part: LNK457D
• Output Voltage: 12 V
• Input / Supply Voltage (max): 265 VAC
• Input / Supply Voltage (min): 90 VAC
• Duty Cycle (max): 39.9 %
• Mounting Style: Through Hole
• Output Current: 350 mA
• Output Power: 5 W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 596-1345

15-Feb-11
RDR-251 – 5 W, PFC, Dimmable LED Power Supply
4.5 LinkSwitch-PL Primary
The LNK457DG device (U1) incorporates the power switching device, oscillator, output
constant current control, start-up, and protection functions. The integrated 725 V
MOSFET provides extended voltage margin and ensures high reliability even during line
surge events. The device is powered from the BYPASS pin via the decoupling capacitor
C9. At start-up, C9 is charged by U1 from an internal current source via the DRAIN pin
and then during normal operation it is supplied by the output via R15 and D4.
The rectified and filtered input voltage is applied to one end 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 an RCD-R clamp
consisting of D2, R13, R12, and C7.
Diode D6 is used to protect the IC from negative ringing (drain voltage ringing below
source voltage) when the MOSFET is off due to the reflected output voltage exceeding
the DC bus voltage, the result of minimal input capacitance to give high power factor.
4.6 Output Rectification
The secondary of the transformer is rectified by D5 and filtered by C11. A Schottky
barrier type was selected for higher efficiency. As C11 provides energy storage during
AC zero crossings its value determines the magnitude of the line frequency output ripple
(2 x f
due to full wave rectification). The value may therefore be adjusted based on the
L
desired output ripple. For the 680 F value shown the output ripple is 50% of I
.
O
Resistor R17 and C10 damp high frequency ringing and improve conducted and radiated
EMI.
4.7 Output Feedback
The CC mode set-point is determined by the voltage drop that appears across R18 which
is then fed to the FB pin of U1. Output overvoltage protection is provided by VR2 and
R14 (the effect of R14 on the current sense signal in negligible and can be ignored).
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