LR645N5-G Supertex, LR645N5-G Datasheet - Page 4

• Manufacturer Part Number: LR645N5-G
• Description: Linear Regulators - Standard Fixed/Adj Hi In V
• Manufacturer: Supertex

Specifications of LR645N5-G

• Polarity: Positive
• Number Of Outputs: 1
• Output Type: Fixed
• Output Voltage: 10 V
• Output Current: 0.03 A
• 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: 1800 mW
• Mounting Style: Through Hole
• Package / Case: TO-220
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LR645: High Current SMPS Start-Up Circuit
The 8 lead version of the LR645 has connections for an ex-
ternal depletion-mode MOSFET for higher output current and
external resistors for adjustable output voltage. As shown in
Figure 2, the output current is increased to 150mA by using
the Supertex 400V depletion-mode MOSFET DN2540. The
maximum operating input voltage will be limited by the drain-
to-source breakdown voltage of the external MOSFET, but
cannot exceed the 450V rating of the LR645.
Figure 2: High Current SMPS Start-Up Circuit
LR645: Off Line Linear Regulator
Circuits requiring low voltages to operate logic and analog
circuits benefit from the LR645. 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 controls, and
low voltage power supplies for appliances such as washing
machines, dishwashers, and refrigerators.
The wide operating input voltage range of 15 to 450V as well
as the ripple rejection ratio of 50dB minimum allows the use
of a 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: Cascading for Precision
A C Line
277V
24V
to
Note: When used with the DN25, +V
–
+
400V
15V
to
C
1.0µF
IN
LR6
C
IN
GND
DN2540
LR645
C
0.1µF
GATE
OUT
●
IN
ACSA
1235 Bordeaux Drive, Sunnyvale, CA 94089
is not connected on the LR6.
Max
875
TRIM
V
OUT
± 0.002V
0 to 3m A
R2
R1
5.000V
@
C
OUT
4
The output voltage can be adjusted from 8 to 12V with 2 ex-
ternal resistors, R1 and R2. The ratio of R2/R1 determines
the output voltage. R2 is connected between the V
TRIM pins. R1 is connected between TRIM and GND pins.
Figure 5 is a curve showing output voltage versus resistor
ratio R2/R1. The optimum range for R1 + R2 is 200KΩ to
300KΩ. This minimizes loading and optimizes accuracy of
the output voltage. Figure 5 uses an R1 + R2 of 250KΩ.
Figure 3 shows the LR645 as a pre-regulator to a precision-
regulator for high precision regulation. Higher output cur-
rent is also possible by using an external depletion-mode
MOSFET DN2540N5 as shown in Figure 4.
Power Dissipation Considerations
The LR645 is a true linear regulator. Its power dissipation is-
therefore a function of input voltage and output load current.
Forexample, if the LR645 is providing a continuous load cur-
rent of 3mAat 10V while its input voltage is 400V, total dis-
sipation in the LR645 will be:
The 1.23 watts is for continuous operation. This is within the
dissipation capabilities of the TO-220 and SOT-89 packag-
es. See the thermal characteristics chart on page 2 for derat-
ings. 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
typically a few hundred milliseconds. All package types of
the LR645 have been characterized for use with a C
least 10µF, and an AC line of 277V.
V
CC
P
= (400V - 10V) x (3.0mA + 150µA)
= 1.23 Watts
DISS
PWM IC
●
= (V
Tel: [phone]
IN
- V
OUT
) x (I
OUT
●
+ I
www.supertex.com
MAX QUIESCENT
)
5.0V
V
+
–
AUX
LR645
OUT
= 12V
OUT
OUT
, but is
of at
and