for the HP 42S
AVR - Adjustable voltage regulator (such as LM317 or TL431) solver program / HP 42S

Circuit diagram (simplified)
Usage : [SOLVER] [AVR]

Variables to be used

Program list
AVR - Rev.1.00 : Aug. 12 2011
00 { 104-Byte Prgm }
01 LBL "AVR"
02 MVAR "Vo"
03 MVAR "Vr"
04 MVAR "Iq"
05 MVAR "R1"
06 MVAR "R2"
07 XEQ 00
08 RCL "R2"
09 ENTER
10 RCL× "Iq"
11 X<>Y
12 RCL÷ "R1"
13 1
14 +
15 RCL× "Vr"
16 +
17 RCL- "Vo"
18 RTN
19 LBL 00
20 RCL "R1"
21 X≤0?
22 240
23 STO "R1"
24 RCL "Vr"
25 X≤0?
26 1.25
27 STO "Vr"
28 0.01
29 %
30 +
31 RCL "Vo"
32 X>Y?
33 RTN
34 X<>Y
35 STO "Vo"
36 RTN
37 .END.

Example
Input (LM317)Input (TL431)
Vo = 4.5   [V]
Vr = 1.25  [V]
Iq = 50E-6 [A]
R1 = 240   [Ω]
R2 = 240   [Ω] (to be solved)
Vo = 3.3   [V]
Vr = 2.495 [V]
Iq = 2E-6  [A]
R1 = 10E3  [Ω]
R2 = 10E3  [Ω] (to be solved)
Output (LM317)Output (TL431)
x: 618.066561014E0
x: 3.20079522865E3
DOWNLOAD
'AVR-1.0' (avr.raw, 107 byte, raw program file for the Free42)

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