4

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:

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

µF 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.

LR645

LR6

Max

875

ACSA

5.000V

± .002V @

0 to 3mA

AC Line

(24 to

277VAC)

1

µF

.01

µF

Figure 3: Cascading for Precision

12

10

8

2.5

3.0

4.0

3.5

Resistor Ratio, R2/R1

R1 + R2 = 250K

Ω

Figure 5:

Typical Output Voltage vs. Resistor Ratio

AC Line

(24 to

277VAC)

5.0V

0 to

150mA

5.0V

Reg

+

–

Gate

DN2540N5

GND

LR645LG

Figure 4:

High Current

Regulator

=

(400V - 10V) x (3.0mA + 150

µA)

=

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

hundred milliseconds.

All package types of the LR6 have been characterized for use

with a C

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11/12/01

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