LR745
High Input Voltage
SMPS Start-up Circuit
Ordering Information
Maximum Input
Voltage
450V
Order Number / Package
TO-92
LR745N3
TO-243AA*
LR745N8
Product marking for TO-243AA:
LR7❋
where
❋
= 2-week alpha date code
*Same as SOT-89. Product supplied on 2000 piece carrier tape reels.
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
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
CC
voltage below their start threshold
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.
Applications
❏
Notebook and Laptop computers
❏
Telecommunication power supplies
❏
Battery chargers
❏
Motor controller
Pin Configuration
Absolute Maximum Ratings
Input Voltage
Output Voltage
Operating and Storage Temperature
Soldering Temperature*
*Distance of 1.6mm from case for 10 seconds
450V
25V
–55°C to 150°C
300°C
1
2
3
TAB
TO-243AA
(SOT-89)
123
TO-92
V
IN
TO-92
TO-243AA
1
1
GND
2
2, TAB
V
OUT
3
3
For detailed circuit and application information, please refer
to application notes AN-H28 and AN-H29.
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.
1
SUPERTEX [ Supertex, Inc ]
