Rev. H 02/09

7

TNY263-268

www.powerint.com

Figure 14. 2.5 W Constant Voltage, Constant Current Battery Charger with Universal Input (85-265 VAC).

PI-2706-021809

+ 5 V

500 mA

RTN

D1

1N4005

C1

3.3

μF

400 V

Fusible

RF1

8.2

Ω

C3

0.1

μF

C7

10

μF

10 V

85-265

VAC

L1

2.2 mH

D2

1N4005

D3

1N4005

D4

1N4005

R2

200 k

Ω

U2

LTV817

D5

1N5819

Shield

L2

3.3

μH

C5

330

μF

16 V

C2

3.3

μF

400 V

C6

100

μF

35 V

R7

100

Ω

R4

1.2

Ω

1/2 W

Q1

2N3904

R8

270

Ω

VR1

BZX79-

B3V9

3.9 V

U1

TNY264

C3

2.2 nF

D6

1N4937

R6

1

Ω

1/2 W

T1

R1

1.2 k

Ω

1

8

4

5

R3

22

Ω

R9

47

Ω

C8 680 pF

Y1 Safety

TinySwitch-II

D

S

BP

EN/UV

reducing the no-load power consumption and improving full-

load efficiency.

Current Limit Operation

Each switching cycle is terminated when the DRAIN current

reaches the current limit of the TinySwitch-II. Current limit

operation provides good line ripple rejection and relatively

constant power delivery independent of input voltage.

BYPASS Pin Capacitor

The BYPASS pin uses a small 0.1

μF ceramic capacitor for

decoupling the internal power supply of the TinySwitch-II.

Application Examples

The TinySwitch-II is ideal for low cost, high efficiency power

supplies in a wide range of applications such as cellular phone

chargers, PC standby, TV standby, AC adapters, motor

control, appliance control and ISDN or a DSL network

termination. The 132 kHz operation allows the use of a low

cost EE13 or EF12.6 core transformer while still providing good

efficiency. The frequency jitter in TinySwitch-II makes it

possible to use a single inductor (or two small resistors for

under 3 W applications if lower efficiency is acceptable) in

conjunction with two input capacitors for input EMI filtering.

The auto-restart function removes the need to oversize the

output diode for short circuit conditions allowing the design to

be optimized for low cost and maximum efficiency. In charger

applications, it eliminates the need for a second optocoupler

and Zener diode for open loop fault protection. Auto-restart

also saves the cost of adding a fuse or increasing the power

rating of the current sense resistors to survive reverse battery

conditions. For applications requiring undervoltage lock out

(UVLO), such as PC standby, the TinySwitch-II eliminates

several components and saves cost. TinySwitch-II is well

suited for applications that require constant voltage and

constant current output. As TinySwitch-II is always powered

from the input high voltage, it therefore does not rely on bias

winding voltage. Consequently this greatly simplifies designing

chargers that must work down to zero volts on the output.

2.5 W CV/CC Cell-Phone Charger

As an example, Figure 14 shows a TNY264 based 5 V,

0.5 A, cellular phone charger operating over a universal input

range (85 VAC to 265 VAC). The inductor (L1) forms a π-filter

in conjunction with C1 and C2. The resistor R1 damps

resonances in the inductor L1. Frequency jittering operation of

TinySwitch-II allows the use of a simple π-filter described

above in combination with a single low value Y1-capacitor (C8)

to meet worldwide conducted EMI standards. The addition of

a shield winding in the transformer allows conducted EMI to be

met even with the output capacitively earthed (which is the

worst case condition for EMI). The diode D6, capacitor C3

and resistor R2 comprise the clamp circuit, limiting the leakage

inductance turn-off voltage spike on the TinySwitch-II DRAIN

pin to a safe value. The output voltage is determined by the

sum of the optocoupler U2 LED forward drop (~1 V), and Zener

diode VR1 voltage. Resistor R8 maintains a bias current

through the Zener diode to ensure it is operated close to the

Zener test current.