Design Idea DI-61

<200 mW No-load Consumption

DI-61

®

Application

Charger

TNY264P

5 V, 600 mA

Power Output

3 W

Input Voltage

Output Voltage

Topology

Device

85-265 VAC

Flyback

Figure 1. TinySwitch-II 3.0 W Cell Phone Charger.

Design Highlights

• Less than 200 mW no-load power consumption (for

115 or 230 VAC input)

• Meets CISPR-22 Class B without Y capacitor

• Low cost, low component count solution

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 key performance characteristic of the circuit shown is the

extremely low no-load consumption of <200 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.

The no-load performance is achieved by use of TinySwitch-II,

and by careful transformer design.

The circuit meets CISPR-22 Class B conducted EMI limits

without a Y capacitor, and therefore has very low AC leakage

current. This EMI performance is achieved via the

TinySwitch-II internal jitter, use of a shield winding, an

output RC snubber, and the primary RCD clamp.

Key Design Points

• Minimize secondary circuit bias currents. Use low current

feedback Zeners for best tolerance. The very low Zener

bias current in this design will provide approximately

±10% output voltage tolerance. A precision reference

(e.g. TL431) can be used if higher precision is required.

• Design transformer with low reflected voltage to minimize

clamp losses. A larger device (TNY266) may allow further

reduction in V

• Wind transformer for lowest leakage inductance. Choose

wire gauges to completely fill winding layers.

• Winding the transformer with tape between primary layers

further reduces intra-winding capacitance and no-load

consumption.

• Resistor R7 limits the peak current into the optocoupler

LED to prevent damage during unusual transients.

PI-3681-031204

D

S

BP

EN

85 - 265

VAC

RTN

N

L

5 V, 0.6 A

RF1

8.2

Ω

1.0 W

D1

1N4005

D2

1N4005

D3

1N4005

D4

1N4005

C1

4.7

µF

400 V

L1

1.0 mH

C3

390 pF

1 kV

C5

470 pF

D5

1N4007G

U1

TNY264P

L2

Bead

2.2

µH

C4

0.1

µF

50 V

U2

PC817A

D7

11DQ06

8T

24 AWG

15T

2 x 32 AWG

102T

33 AWG

18

7

3

4

T1 EE13

L

2

C6

470

µF

10 V

U2

R5

820

Ω

R6

2.4

Ω

2 W

R4

1.5 k

Ω

R7

4.7

Ω

R3

33

Ω

R1

100 k

Ω

R2

330

Ω

1/2 W

L3

Ferrite

Bead

VR3

BZX79B5V1

C7

100

µF

10 V

C2

4.7

µF

400 V

Q1

2N3906

TinySwitch-II

www.powerint.com

March 2004