( )

OUT

REF

ADJ

R

V

= V

I

R

R

2

2

1

1

æ

ö

+

+

ç

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LM117HV, LM317HV

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SNVS773D – APRIL 2000 – REVISED SEPTEMBER 2015

8 Detailed Description

8.1 Overview

In operation, the LM317HV develops a nominal 1.25-V reference voltage, VREF, between the output and

adjustment terminal. The reference voltage is impressed across program resistor R1 and, since the voltage is

constant, a constant current I1 then flows through the output set resistor R2, giving an output voltage calculated

by Equation 1:

(1)

Figure 13. Adjustable VOUT Through R1 and R2

Because the 100-

μA current from the adjustment terminal represents an error term, the LM317HV was designed

to minimize IADJ and make it very constant with line and load changes. To do this, all quiescent operating current

is returned to the output establishing a minimum load current requirement. If there is insufficient load on the

output, the output will rise.

8.2 Functional Block Diagram

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