DI-34 데이터 시트보기 (PDF) - Power Integrations, Inc
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DI-34 Datasheet PDF : 2 Pages
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Design Idea DI-34
TinySwitch-®II
5 W Universal Adapter
Application Device
Adapter TNY266P
Power Output
5W
Input Voltage
85-265 VAC
Output Voltage
5V
Topology
Flyback
Design Highlights
• Simple design: low parts count (23)
• <300 mW no-load without transformer bias winding
• Frequency jittering reduces EMI - meets EN55022 Class B
with no Y capacitor: very low primary-to-secondary leakage
current
• ±7% output tolerance with simple Zener reference
• High Frequency (132 kHz) operation allows small, low cost
EE16 transformer
• Built-in thermal shutdown protection
• ON/OFF digital regulation: No analog control loop to
compensate
Operation
Figure 1 is a simple flyback converter utilizing several
TinySwitch-II built-in features such as switching frequency
jittering, thermal shutdown and auto-restart fault protection.
Typical applications are wall mount adapters and other AC/DC
applications requiring very low cost and small size. The ability
to meet EMI requirements with no Y capacitor makes this
circuit ideal for applications requiring low primary-to-secondary
leakage currents.
The TinySwitch-II frequency jitter feature and transformer
construction allow use of a simple filter (L1, L2, C1 and C2)
to meet EMI requirements with L2 used to attenuate high
frequency EMI in the radiated spectrum (>30 MHz). The
circuit also uses a low cost RCD clamp (C7, D5, R3, and R4).
Diode D5 is a Glass Passivated (GP) general purpose diode,
allowing partial recovery of the leakage energy by
recirculating clamp current during the D5 reverse recovery
time, thus improving efficiency. Resistor R3 reduces EMI by
limiting the peak D5 reverse current and thus softening its
recovery characteristic.
The combined voltage drops of Zener diode (VR7) and
optocoupler diode (U2) set the output voltage. Resistor R7
biases VR7 according to its specification. The TinySwitch-II
feedback current is independent of load allowing ±7% output
voltage tolerance with this simple Zener reference.
Due to the digital nature of the TinySwitch-II control scheme,
no loop compensation is required. In addition, the current
transfer ratio (CTR) of the optocoupler is not critical and no
DC gain setting resistor in series with VR7 is required.
RF1
8.2 Ω
2W
L
85 - 265
VAC
N
D1
D2
1N4005 1N4005
L1
1.0 mH
C7
1.0 nF
1 kV
R3
100 Ω
R4
200 kΩ
1/2 W
D5
1N4005 GP
C1
6.8 µF
400 V
C2
6.8 µF
400 V
D3
D4
1N4005 1N4005
L2
Bead
TinySwitch
U1
TNY266P
D
EN
BP
S
C3
0.1 µF
50 V
T1
EE-16
NC
1
5
4
8
3
D6
1N5822
C4
1000 µF
10 V
2
U2
PC817A
L3
3.3 µH
1.0 A
VR7 BZX79C3V9, 2%
5 V, 1.0 A
C5
470 µF
10 V
RTN
R7
150 Ω
Figure 1. TinySwitch-II – TNY266P, 5 V, 1 A, 5 W Charger-Adapter Power Supply.
PI-3326-051303
DI-34
www.powerint.com
May 2003
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