7

TNY263-268

G

4/05

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

PI-2706-080404

+ 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

The TinySwitch-II does not require a bias winding to provide

power to the chip, because it draws the power directly from

the DRAIN pin (see Functional Description above). This

has two main benefits. First, for a nominal application, this

eliminatesthecostofabiaswindingandassociatedcomponents.

Secondly, for battery charger applications, the current-voltage

characteristic often allows the output voltage to fall close to

zero volts while still delivering power. This type of application

normally requires a forward-bias winding which has many

more associated components. With TinySwitch-II, neither are

necessary.Forapplicationsthatrequireaverylowno-loadpower

consumption (50 mW), a resistor from a bias winding to the

BYPASS pin can provide the power to the chip. The minimum

recommended current supplied is 750 µA. The BYPASS pin in

thiscasewillbeclampedat6.3V.Thismethodwilleliminatethe

power draw from the DRAIN pin, thereby 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

singleinductor(ortwosmallresistorsforunder3Wapplications

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 under-voltage 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.