DI-84 Datasheet, PDF (1/2 Pages) Power Integrations, Inc. – 3 W Charger: <30 mW No-load Consumption

Design Idea DI-84
TinySwitch^®-II 3 W Charger:
<30 mW No-load Consumption
Application
Charger
Device
TNY264P
Power Output
3W
Input Voltage
85-265 VAC
Output Voltage
5 V, 600 mA
Topology
Flyback
Design Highlights
• Less than 30 mW no-load power consumption (for
115/230 VAC input)
• Meets CISPR-22 Class B without Y capacitor
• Low cost, low component count solution
• Meets CEC active mode efficiency with good margin
The bias winding should provide enough current to fully
disable the internal current source at no-load. Other load
conditions are not important, as the device will be powered
from the DRAIN pin if bias is lost. This allows a simple
flyback winding to be used. Figure 2 shows that the bias
winding and choice of R2 should provide approximately
600 µA at no-load to minimize consumption.
Operation
The TinySwitch-II flyback converter in Figure 1 generates
a constant voltage, constant current (CV/CC) 5 V, 600 mA
output. Typical applications include wall-mounted chargers
for cell phones, PDAs and other battery powered portable
equipment.
The circuit meets CISPR-22 Class B conducted EMI limits
without a Y capacitor, and therefore has very low AC leakage
current. Superior EMI performance is achieved via the
TinySwitch-II frequency jitter, an output RC snubber, use of
the bias winding as a shield, and careful selection of clamp
Zener voltage.
The key performance characteristic of the circuit shown is
Key Design Points
the extremely low no-load consumption of <30 mW. A linear
transformer charger of similar rating will typically consume
1 W to 4 W at no-load. At $0.12/kWh, the TinySwitch-II can
therefore reduce energy costs by $1 to $4 per year.
• Design bias winding circuit to provide approximately
600 µA at no-load. Figure 2 shows the details.
• Minimize secondary circuit bias currents. Use low current
feedback Zeners for best tolerance. The very low Zener
This no-load performance is achieved by using a transformer
bias winding as a low voltage source for TinySwitch-II operating
current. Even without this winding, a TinySwitch-II circuit will
consume <300 mW at no-load. The bias winding disables the
internal high voltage current source, which normally powers
the IC from the DRAIN pin, thereby further reducing power
consumption.
L1
1.0 mH
T1
T1 EE13
L_P = 1.9 mH
1
8
bias current in this design will provide better than ±10%
output voltage tolerance.
• Design transformer with low reflected voltage to minimize
clamp losses.Alarger device (TNY266) may enable further
reduction in V_OR.
• Wind transformer for lowest leakage inductance. Choose
wire gauges to completely fill winding layers.
R6
33 Ω
C3
470 pF
100V
D7
11DQ06
L3
Ferrite
Bead
5 V, 0.6 A
D1
D2
RF1 1N4005 1N4005
8.2 Ω
L
1.0 W
Fusible
85 - 265
VAC
C1
4.7 µF
400V
N
D3
D4
1N4005 1N4005
L2
Ferrite
Bead
VR1
BZY97-
C130
102T
8T
24 AWG T.I.
7
D5
1N4007G
C2
32 AWG
R1
2
200 Ω
1/2 W
3
15T
32 AWG
4
D6
1N4148
C5
47 µF
16 V
4.7 µF
400V U1
TNY264P
D
EN/UV
TinySwitch-II
BP
S
C4
0.1 µF
50 V
U2
PC817A
C6
470 µF
10 V
R2
Q1
9.2 kΩ _2N3906
R4
820 Ω
R5
2.4 Ω
2W
R3
1.5 kΩ
C7
100 µF
10V
VR2
BZX79-
B5V1
RTN
Figure 1. TinySwitch-II 3.0 W Cell Phone Charger.
PI-3659-060205
DI-84
www.powerint.com
June 2005