LR645
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
0.01碌F 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.
P
DISS
=
=
=
(V
IN
- V
OUT
) x (I
OUT
+ I
MAX QUIESCENT
)
(400V - 10V) x (3.0mA + 150碌A)
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 C
OUT
but is typically a few
hundred milliseconds.
All package types of the LR6 have been characterized for use
with a C
OUT
of at least 10碌F , and an AC line of 277V.
Figure 5:
Typical Output Voltage vs. Resistor Ratio
Figure 3:
Cascading for Precision
12
LR6
AC Line
(24 to
277VAC)
C
IN
1碌F
Max
875
ACSA
C
OUT
.01碌F
Output Voltage
5.000V
鹵
.002V @
0 to 3mA
10
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:
R1 + R2 = 250K鈩?/div>
8
2.5
3.0
3.5
4.0
Resistor Ratio, R2/R1
Figure 4:
High Current
Regulator
DN2540N5
AC Line
(24 to
277VAC)
Gate
LR645LG
V
OUT
C
OUT
5.0V
Reg
5.0V
+
0 to
150mA
鈥?/div>
C
IN
GND
11/12/01
漏2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
4
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 744-0100 鈥?FAX: (408) 222-4895
www.supertex.com
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