LR645(2001) Ver la hoja de datos (PDF) - Supertex Inc
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LR645 Datasheet PDF : 4 Pages
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LR6:Off Line Linear Regulator
Circuits requiring low voltages to operate logic and analog
circuits benefit from the LR6. The conventional use of step down
transformers can be eliminated thereby saving space and cost.
Some examples of these applications are proximity controlled
light switches, street lamp control, and low voltage power supplies
for appliances such as washing machines, dishwashers, and
refrigerators.
The wide operating input voltage range of 15V to 450V as well as
the ripple rejection ratio of 50dB minimum allow the use of small
high voltage input capacitor. The input AC line can be either full-
wave or half-wave rectified. A minimum output capacitance of
0.01µF is recommended for output stability.
Figure 3 shows the LR6 as a pre-regulator to a precision
regulator for high precision regulation. Higher output current is
also possible by using an external depletion-mode MOSFET
DN2540N5 as shown in Figure 4.
Figure 3: Cascading for Precision
AC Line
(24 to
277VAC)
LR6
CIN
1µF
Max
875
ACSA
5.000V
COUT ± .002V @
.01µF 0 to 3mA
Power Dissipation Considerations
The LR6 is a true linear regulator. Its power dissipation is
therefore a function of input voltage and output load current. For
example, if the LR6 is providing a continuous load current of 3mA
at 10V while its input voltage is 400V, total dissipation in the LR6
will be:
LR645
PDISS =
=
(VIN - VOUT) x (IOUT + IMAX QUIESCENT)
(400V - 10V) x (3.0mA + 150µA)
=
1.23 Watts
The 1.23 watts is for continuous operation. This is within the
dissipation capabilities of the TO-220 and SOT-89 packages.
See Page 14-2, thermal characteristics, for deratings.
For SMPS start-up applications, the output current is usually
required only during start-up. This duration depends upon the
auxiliary supply output capacitor and COUT but is typically a few
hundred milliseconds.
All package types of the LR6 have been characterized for use
with a COUT of at least 10µF , and an AC line of 277V.
Figure 5:
Typical Output Voltage vs. Resistor Ratio
12
10
R1 + R2 = 250KΩ
8
2.5
3.0
3.5
4.0
Resistor Ratio, R2/R1
Figure 4:
High Current
Regulator
AC Line
(24 to
277VAC)
DN2540N5
Gate
LR645LG
VOUT
5.0V
Reg
CIN
COUT
GND
5.0V
+
0 to
150mA
–
©2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
4
11/12/01
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 744-0100 • FAX: (408) 222-4895
www.supertex.com
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