RDK-252 Power Integrations, RDK-252 Datasheet - Page 22

• Manufacturer Part Number: RDK-252
• Description: KIT REF DESIGN DG CAPZERO
• Manufacturer: Power Integrations
• Series: CAPZero™r
• Type: Other Power Managementr

Specifications of RDK-252

• Main Purpose: Automatic X Capacitor Discharge
• Embedded: No
• Utilized Ic / Part: CAP014DG, CAP002DG, CAP012DG
• Primary Attributes: Low No-Load Input Power (
• Secondary Attributes: Surge Testing to EN6100-4-5 Class 4
• Input Voltage: 85 V to 264 V
• Board Size: 38.1 mm x 25.4 mm
• Product: Power Management Modules
• Dimensions: 38.1 mm x 25.4 mm
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: CAP014DG
• Other names: 596-1313

Rev. A 030910
Figure 28. Externally Set Current Limit, Fast AC Latch Reset and Brownout.
As the secondary feedback current is sourced from the output,
it represents an output load and therefore lowering the
feedback current reduces this load and hence input power
consumption. As the reduction is a function of the output
voltage this approach is most effective for designs where the
output feedback is derived from higher output voltage (>12 V).
Transistor Q
stability a small value resistor (20 W) should be added from the
emitter of Q
base of Q
compensates for optocoupler leakage current. This is also the
reason the gain of the optocoupler should be limited to a CTR
rank of A (80-160%) to ensure that at high temperature the
leakage of the optocoupler transistor doesn’t modulate the
feedback current.
On the secondary side the optocoupler LED series resistor (R16
in Figure 31) should be increased to correctly set the overall
loop gain. A value of 10 times that of a standard feedback
configuration is a good initial estimate which can then be
adjusted based on the control loop bode plot.
Use of TLV431 vs. TL431 Secondary Reference IC
In high voltage output designs (>12 V) switching from a TL431 to
TLV431 can reduce no-load consumption by reducing the bias
current needed by the reference IC. For correct operation the
TL431 requires a supply current of 1 mA whereas for the
TLV431 this is reduced to 100 µA. This reduction in supply
current (fed from a resistor in parallel to the optocoupler LED)
directly reduces the output loading and therefore input power.
Implementing Overvoltage Protection Feature
Using TOPSwitch-JX
The bias winding output tracks the changes in the output
voltage for the flyback topology. If the feedback loop fails and
results in an increase in output voltage, the voltage of the bias
winding will also increase. This can be used to detect an output
overvoltage condition (Figures 20, 21).
A suitable Zener diode with a series resistor connected between
the bias winding output and the V pin can be selected such that
the Zener diode conducts once the bias winding voltage rises
22
Voltage
Application Note
Input
X
DC
+
-
to the emitter of the optocoupler transistor
X
X
to the CONTROL pin. A second resistor from the
can be any general purpose NPN type. For
D
S
CONTROL
Typ. 65 VAC brownout threshold.
<3 s AC latch reset time.
Higher gain Q
decreasing C1 for lower no-load input
power.
X
R
IL
Q
C
R
R
allows increasing R1/
39 kΩ
4 MΩ 1N4007
R2
R1
PI-5652-110609
47 nF
C1
Input
AC
Figure 30. Implementation of Accurate Over-Current Protection Circuit.
significantly (typically 20 % to 30 %) above the highest voltage
at the output of the bias winding during normal operation (or
under a transient loading condition during normal operation).
A current injected in the V pin in excess of 112 µA will result in
the switching cycle being terminated instantaneously. If the
injected current remains higher than 112 µA for over 100 µs, the
part will enter hysteretic OV shutdown. In such a situation,
switching will resume as soon as the injected current reduces
below the hysteresis point after completing an auto-restart cycle.
If the injected current exceeds 112 µA, the V pin responds by
dropping the V pin voltage by 0.5 V. If the drop in V pin voltage
causes the V pin current to jump to a value higher than 336 µA,
the part enters a state of latched shutdown. If the value of the
series resistor R
the change of V pin voltage in response to the injected current
reaching 112 µA is adequate to cause a current in excess of
336 µA to flow which results in latched overvoltage condition,
requiring a reset. In this state the operation will not resume
unless the input AC is cycled and the C pin capacitor is allowed
to discharge, thereby resetting the part. Alternatively the latch
may also be reset by disconnecting the X pin from the S pin.
The TOPSwitch-JX stops switching and resets the OVP latch
when it detects that less than 27 µA is being pulled out of the
X pin.
This property is used in the Fast AC Reset circuit shown In
Figure 28. The figure shows a simple internal latch reset circuit
using a single BJT. The voltage on capacitor C1 changes much
more rapidly as compared to the bulk capacitor allowing for a
fast reset of the latch when the AC is cycled.
Figure 29.
V Pin
To
R
OCP
UF4005
Using TOP269-271.
From
V
Recommended RCD Circuit for Higher Power Designs
BIAS
OVP
100 Ω
R5
U3A
is very small (in the range of 5 W to 22 W),
10 pF - 33 pF
22 Ω - 150 Ω
1/2 W
51.1 kΩ
LM321
1 kV
U2
R6
0.22 µF
+
C1
R
C
D
S
2.43 kΩ
100 kΩ
R3
R2
CONTROL
From V
X
www.powerint.com
R
V
IL
10 kΩ
F
O
R1
0.006 Ω
R
PI-5828-030310
TLV431
PI-5004-012010
SENSE
C
U1
AN-47
RTN