8

LR8

LR8

Application Note

AN-H40

Operation

Except for it’s higher voltage rating, the LR8 operates like any

other 3-terminal adjustable linear regulator.

A simple resistive divider sets the output voltage while a capacitor

at the output improves transient response and ensures regulator

stability. When applicable, an input capacitor is required to

provide energy storage for rectified AC.

Keeping in mind that the LR8 requires at least a 10V difference

between input and output for proper operation, the minimum

Introduction

The LR8 is a high voltage 3-terminal adjustable linear regulator.

Intended for operation directly off rectified AC mains, the LR8

operates at input voltages up to 450 volts, making it compatible

with line voltages up to 240 VAC. It’s output voltage adjustability

assures that it can be used in most any application. The LR8 is

ideally suited for low power off-line DC power supplies and

SMPS start-up circuits.

Available in a leaded TO-92 package and a surface mount

SOT-89 and D-PAK package, it is ideal for applications where

space is at a premium.

Relevant specifications are shown in the table below.

Input Voltage Range

Output Voltage Range

Output Voltage Accuracy

±5%

Power Dissipation

TO-92:

0.74W

TO-243AA (SOT-89):

1.6W

TO-252 (D-PAK):

2.5W

Output Current

0.5 to 10mA

Load Regulation

3%

Line Regulation

0.01%/V

Supply Rejection

60dB typ @120Hz

LR8 Specifications

CI

t

VV

IN

LOAD

IN pk

OUT

>

−−

()

10V

where

I

LOAD

= Load current

t= Time between peaks of input

waveform

V

IN(pk)

= Peak input voltage

V

OUT

= Output voltage

Note that the LR8 requires a minimum of 0.5mA load current for

proper operation. The current through the resistive divider may

be included as part of the minimum load.

High Voltage Linear Regulators and

Constant Current Sources Using LR8

by Scott Lynch, Senior Applications Engineer

LR8 Block Diagram and Typical Application

Overtemp &

Overcurrent

10µA

1.2V

ADJ

LR8

Pass

Element

≥ 1µF

Load

Supply

V

R

R

R











 +µ

12

1

10

2

1

2

.•

vA