RDK-201 Power Integrations, RDK-201 Datasheet - Page 8

• 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

Rev. E 09/09
Drain Clamp
Recommended Clamp Circuits
Components R1, R2, C3, VR1 and D5 in fi gure 4 comprise the
clamp. This circuit is preferred when the primary leakage
inductance is greater than 125 μH to reduce drain voltage
overshoot or ringing present on the feedback winding. For best
output regulation, the feedback voltage must settle to within 1%
at 2.1 μs from the turn off of the primary MOSFET. This requires
careful selection of the clamp circuit components. The voltage of
VR1 is selected to be ~20% above the refl ected output voltage
(V
conduction during the fl yback voltage interval when the output
diode is conducting. The value of R1 should be the largest value
that results in acceptable settling of the feedback pin voltage and
peak drain voltage. Making R1 too large will increase the
discharge time of C3 and degrade regulation. Resistor R2
dampens the leakage inductance ring. The value must be large
enough to dampen the ring in the required time but must not be
too large to cause the drain voltage to exceed 680 V.
If the primary leakage inductance is less than 125 μH, VR1 can
be eliminated and the value of R1 increased. A value of 470 kΩ
with an 820 pF capacitor is a recommended starting point.
Verify that the peak drain voltage is less than 680 V under all
line and load conditions. Verify the feedback winding settles to
an acceptable limit for good line and load regulation.
Effect of Fast (500 ns) versus Slow (2 μs) Recovery
Diodes in Clamp Circuit on Pulse Grouping and Output
Ripple.
A slow reverse recovery diode reduces the feedback voltage
ringing. The amplitude of ringing with a fast diode represents
8% error in Figure 10.
Figure 9.
OR
8
). This is to clip any turn off spike on the drain but avoid
RCD Clamp, Low Power or Low Leakage Inductance Designs.
LNK623-626
R
C2
R
D
C1
C1
PI-5107-110308
C
C1
RCD Clamp With Zener Bleed. High Power or High Leakage Inductance Designs.
Figure 10. Effect of Clamp Diode on Feedback Pin Settling. Clamp Circuit (top).
Black Trace: D
Gray Trace: D
Feedback Pin Voltage (bottom).
C1
C1
is a 1N4007G (standard recovery, trr = 2 us)
is a FR107 (fast type, trr = 500 ns)
D
R
C2
R
C2
C2
D
R
C1
C1
R
D
C1
C1
PI-5108-110308
C
PI-5107-110308
C1
C
C1
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