TNY267P_1 Datasheet, PDF (7/20 Pages) Power Integrations, Inc. – 9W DVD power supply

DER-7
9W DVD power supply using TNY267P
February 4, 2004
5 Circuit Description
This circuit is configured as a flyback using the TNY267.
5.1 Input Rectification
AC input power is rectified by a full bridge, consisting of D1 through D4. The rectified DC
is then filtered by the bulk storage capacitors C1 and C2. Inductor L1, C1 and C2 form a
pi (π) filter, which attenuates conducted differential-mode EMI noise.
5.2 Auxiliary Bias Supply
The auxiliary bias supply circuit is made up of the primary-side transformer bias winding,
diode D9, capacitor C10 and resistor R6. The bias voltage was given just enough current
to disable the internal current source during “DC Switch” operation. In this case, the
standby power consumption is minimized.
5.3 Output Voltage Sensing, Feedback and DC switch
The combined voltage drops of Zener diode Z2 and optocoupler set the main output
voltage. TinySwitch-II feedback current is independent of load allowing tight output
voltage tolerance with this simple Zener circuit. The operation of the TinySwitch allows
the use of a “DC switch” (SW1) to put the power supply in a standby condition, with very
low consumption. The DC switch does not need to be safety-rated, and thus is much
lower cost than an equivalent AC switch. During DC Switch operation, the 5C output is
regulated at 1V, and all other outputs are at 1/5^th of normal output voltage. The DVD
system load is very low during this output voltage condition. The net result is that the
input power is ~200 mW at 230 Vac input. This is possible with TinySwitch-II because of
its EcoSmart features.
6 PCB Layout
Page 7 of 20
Figure 3 Printed Circuit Layout.
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