LR645N8-G Supertex, LR645N8-G Datasheet - Page 3

• Manufacturer Part Number: LR645N8-G
• Description: Linear Regulators - Standard Fixed/Adj Hi In V
• Manufacturer: Supertex

Specifications of LR645N8-G

• Polarity: Positive
• Number Of Outputs: 1
• Output Type: Fixed
• Output Voltage: 1.7 V
• Output Current: 3 mA
• Line Regulation: 200 mV
• Load Regulation: 400 mV
• Input Voltage Max: 450 V
• Maximum Operating Temperature: + 150 C
• Minimum Operating Temperature: - 55 C
• Maximum Power Dissipation: 1600 mW
• Mounting Style: SMD/SMT
• Package / Case: SOT-89 (TO-243AA)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LR645 Block Diagram
LR645: SMPS Start-Up Circuit
One of the main applications for the LR645 is a start-up
circuit for off-line switch-mode power supplies (SMPS), as
shown in Figure1. A minimum output capacitance of 0.01µF
is recommended for stability. The wide operating input volt-
age range of the LR645 allows the SMPS to operate and
start-up from rectified AC or a DC voltage of 15 to 450V with-
out adjustment.
During start-up, the LR645 powers the VCC line of the PWM
IC with a nominal output voltage of 10V. The auxiliary voltage
connected through a diode to the VOUT pin of the LR645 will
start to increase. When the auxiliary voltage becomes larger
Figure 1: SMPS Start-Up Circuit
+
–
450V
15V
to
V
C
IN
IN
LR6
GND
●
TRIM
1235 Bordeaux Drive, Sunnyvale, CA 94089
LR645
C
OUT
V
CC
PWM IC
V
3
IN
–
+
than the output voltage the LR645 turns OFF its internal high
voltage input line and output voltage, allowing the auxiliary
voltage to power the VCC line of the PWM IC. The input
current drawn by the LR645 from the high voltage line after
start-up will therefore only be leakage current of the internal
MOSFET switch, which is typically 0.1µA.
The 3-terminal version shown in Figure 1 has load regula-
tion guaranteed from 0 to 3.0mA at a fixed nominal output
voltage of 10V. Applications requiring higher output current
and/or a different output voltage can use the 8 pin adjustable
version.
●
Tel: [phone]
GATE
GND
V
OUT
●
www.supertex.com
5.0V
V
+
–
AUX
= 12V
LR645