1

TO-243AA

(SOT-89)

Order Number / Package

TO-92

TO-243AA*

450V

LR745N3

LR745N8

*Same as SOT-89. Product supplied on 2000 piece carrier tape reels.

LR745

Ordering Information

High Input Voltage

SMPS Start-up Circuit

Maximum Input

Voltage

V

IN

GND

V

OUT

TO-92

1

2

3

TO-243AA

1

2, TAB

3

Pin Configuration

1 2 3

TO-92

1

3

2

Absolute Maximum Ratings

Input Voltage

450V

Output Voltage

25V

Operating and Storage Temperature

–55

°C to 150°C

Soldering Temperature*

300

°C

*Distance of 1.6mm from case for 10 seconds

TAB

Features

❏ 25V to 450V operating input voltage range

❏ Compatible with industry standard PWM ICs.

See application notes AN-H28 and AN-H29.

❏ Output current limiting

❏ For PWM ICs with start-up threshold voltage

of 13.9V to 18.8V

❏ Very low power consumption after start-up

Applications

❏ Notebook and Laptop computers

❏ Telecommunication power supplies

❏ Battery chargers

❏ Motor controller

General Description

The Supertex LR7 is a high input voltage SMPS start-up circuit.

The LR7 is ideally suited for use with industry standard low

voltage PWM ICs having start thresholds of 13.9V to 18.8V. It

allows the PWM ICs to be operated from rectified 120V or

240VAC lines, and eliminates the use of power resistors often

used for this purpose. The internal circuitry of the LR7 allows the

PWM ICs to operate at a V

voltage after start-up. The auxiliary voltage can be less than the

start threshold voltage, which allows for improved efficiency.

Current from the high voltage line is drawn only during the start-

up period. After start-up, the internal high voltage line is discon-

nected from the IC thereby reducing the continuous power

dissipation to a minimum.

For detailed circuit and application information, please refer

to application notes AN-H28 and AN-H29.

Product marking for TO-243AA:

LR7

❋

where

❋ = 2-week alpha date code

11/12/01

Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability

indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to

workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the

Supertex website: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.