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This is a 15V voltage regulator from Art of Electronics (page 694), and it is supposed to limit the output current to 1A. However, when driving load impedance (R7) low enough, I am getting much higher current than this. Any ideas where could be the problem?

My final goal is to build power supply with a (preferably adjustable) current limiter. enter image description here

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  • 1
    \$\begingroup\$ It looks like the Q2 collector is not connected to Q1 base. \$\endgroup\$
    – G36
    Commented Oct 18, 2023 at 18:46
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    \$\begingroup\$ Did you build this or simulate it? And can the 2n2222 really handle 1 A, and a dissipation of 5 W (20 V - 15 V)*1 A? I don't think so. \$\endgroup\$
    – SteveSh
    Commented Oct 18, 2023 at 18:46
  • \$\begingroup\$ @G36 - Good eye! But would the dot be there without a connection? \$\endgroup\$
    – SteveSh
    Commented Oct 18, 2023 at 18:47
  • \$\begingroup\$ @G36 it is actually connected, it just looks like it is not \$\endgroup\$
    – Atropin
    Commented Oct 18, 2023 at 18:49
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    \$\begingroup\$ tinyurl.com/yl2wv8o5 \$\endgroup\$
    – G36
    Commented Oct 18, 2023 at 19:03

1 Answer 1

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If the simulator model for the U2 amplifier doesn't include a current limit, the intended effect of Q2 is defeated. Put a series resistor in the output, between the C1 and collector connections, to get a real current-limit effect.

Simulators depict real devices, but aren't (internally) as complicated as reality. As others have pointed out, 2N2222 won't carry the intended current.

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  • \$\begingroup\$ Seems like the problem was really with the amplifier, after swapping for another one the limiting is working. Thank you. \$\endgroup\$
    – Atropin
    Commented Oct 18, 2023 at 19:04

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