EPR-000014 Datasheet, PDF (6/28 Pages) Power Integrations, Inc. – Engineering Prototype Report - 3 W Universal Input TinySwitch-II TNY264 Power Supply

EPR-000014 – 9 V, 0.33 A, 3 W TNY264 Adapter
22-Feb-2002
common mode input choke. Class B emissions are achieved for applications requiring
an ‘artificial hand’ tied to secondary return; which makes this design fully compliant with
handheld applications. Standby power consumption is below 250 mW at 230 V_AC input.
TinySwitch-II provides greatly reduced device tolerances and incorporates built-in
hysteretic overtemperature protection. These features minimize component count while
maximizing device power capability. Auto-restart functionality minimizes device thermal
stresses during short-circuit conditions; providing performance similar to that available
with the TOPSwitch families.
A fusible, flameproof resistor (R1) is used in place of a fuse to reduce cost and increase
differential mode filtering. This, combined with the π filter formed by L1, C1 and C2 in
addition to C5, allows the unit to meet EN55022 B (CISPR22 B) conducted emission
standards.
The AC input is rectified and smoothed by D1-4, C1 and C2. The resulting DC bus is
applied to one end of the transformer primary. The other end of the primary is
connected to the TinySwitch-II DRAIN pin. Low cost RCD clamping (R4, C3 & D6) limits
the maximum DRAIN voltage to below 700 V due to transformer leakage inductance. C4
provides the local bypass for TinySwitch-II. This capacitor is kept charged during the off
time of the internal MOSFET, providing the energy to supply the IC.
An optional line sense resistor (R3) implements under-voltage detect. This is
accomplished by sensing the DC voltage across the bulk input capacitors (C1 &C2) at
power-up. TinySwitch-II is disabled until the DC voltage reaches the required level.
With R3 as shown (2 MΩ) this occurs at 100 V_DC. Under-voltage detect ensures that the
outputs are glitch free on power-up and power down, preventing the power supply from
starting if the input voltage is too low, and stopping the supply when the output falls out
of regulation on power down. TinySwitch-II will detect the absence of R3 and disable the
under-voltage function if not required.
The secondary is rectified by D6 and C6. Second stage output filtering consists of ferrite
bead (L2) and output capacitor (C7) which eliminate high frequency switching noise and
reduce output ripple below 100 mVp-p.
VR2 and U2 sense the output voltage. The combined voltage drop of these two
components sets the output voltage to 9 V. A 5% Zener was used giving an overall
tolerance and regulation variation of ±7%. Using a 3% or 2% Zener allows a more tightly
controlled output voltage tolerance.
Power Integrations, Inc.
Tel: [phone] Fax: [phone]
www.powerint.com
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