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DER-121 Fiches technique(PDF) 6 Page - Power Integrations, Inc.

No de pièce DER-121
Description  13.1 W AC-DC Flyback Converter Using TNY268P
Download  24 Pages
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Fabricant  POWERINT [Power Integrations, Inc.]
Site Internet  http://www.powerint.com
Logo POWERINT - Power Integrations, Inc.

DER-121 Fiches technique(HTML) 6 Page - Power Integrations, Inc.

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DER-121
13.1 W adapter – TNY268
November 3, 2005
Page 6 of 24
Power Integrations
Tel: +1 408 414 9200 Fax: +1 408 414 9201
www.powerint.com
4
Circuit Description
A Flyback converter is used to obtain 5.25 V / 2.5 A output from 90-264 VAC input.
Using technical skill of core cancellation and balance shield windings reduce EMI noise.
4.1
Input Rectification and EMI Filtering
Fuse F1 protects the charger against any fault condition, and input current exceeds 1 A.
Diodes D1, D2, D3, and D4 form Full-bridge rectifier, and rectify the AC voltage into DC
voltage and charge the capacitors C1 and C2. L1, L2, C1, and C2 form
π – filter and
attenuate EMI noise. Here, C1 and C2 act as both storage capacitors and part of EMI
filter, which reduces the total cost.
4.2
TOPSwitch Primary
This design uses RCD (C4, D5, R3, and R4) clamping across primary winding to limit the
drain voltage below 700V, when the Mosfet inside U1 turns OFF.
The capacitor C5
connected to BP (by-pass) pin of U1 stores energy and provide power for the internal
circuit of U1 and also to turn ON the U1’s Mosfet, during power-up and steady state
operation. The opto-coupler transistor pulls down enable (EN) pin of U1. TinySwitch-II
keeps on switching as long as the pull down current < 240 µA. U1 will stop switching if
the pull down current exceeds 240 µA.
4.3
Output Rectification
When U1 Mosfet is turned ON, current flows through transformer primary and stores
energy. When U1 is ON, output diode D6 is OFF. When the U1 Mosfet is OFF, D6 is
forward biased, and the stored energy is transferred to the secondary and stores in C6,
C8 and C9. The snubber C7 and R5 across output diode D6 and a bead core in series
with output diode D6 will improve EMI.
4.4
Output Feedback
Resistors R8, R9 divide down the supply output voltage and apply it to the reference pin
of error amplifier U3. Shunt regulator U3 drives optocoupler U2 through resistor R6 to
provide feedback information to the U1 EN pin. Capacitor C10 drive to the optocoupler
during supply startup to reduce output voltage overshoot.
C11 plays a role in
compensating of the power supply feedback loop.


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