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I have been trying to understand the current limiter circuit design. I am having problem decoding them. Could anybody help me understanding this circuit?

Here I_VCC_AUX is 12 V and R247 comes from a monostable multivibrator circuit and the output goes to actuator.

schematic

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  • \$\begingroup\$ 1) and the output goes to actuator. I see no output on your schematic. Yes I know it is probably the right side of L208 but I don't want to guess, you need to make it clear in your schematic. 2) regarding the circuit, look at the circuit in Figure 6 on this page en.wikipedia.org/wiki/Current_source in Wikipedia Replace the zener DZ1 with a diode and you have a similar circuit. Only difference is that the output is taken from the botton instead of from the collector of the NPN. The end result is very similar, the circuit prevents that more current flows than a certain value. \$\endgroup\$
    – Bimpelrekkie
    Commented Mar 13, 2021 at 16:26

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Note the red arrows I've added: -

enter image description here

Because there will be approximately one forward diode drop (0.6 to 0.8 volts) across R243, there has to be a current flowing through R243 that cannot exceed approximately 0.7 volts ÷ 0.5 Ω = 1.4 amps. Hence the circuit current limits at about 1.4 amps.

The signal into R247 is used to turn off the pass transistor i.e. it acts like an enable input.

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  • \$\begingroup\$ How does the transistors Q205, Q203 function in this circuit \$\endgroup\$
    – Sudhir Kumar
    Commented Mar 14, 2021 at 16:42
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    \$\begingroup\$ Do you actually mean Q204 and Q205 - they together from an on-off circuit that disables or enables Q203. Q203 is the current limiting transistor @SudhirKumar \$\endgroup\$
    – Andy aka
    Commented Mar 14, 2021 at 16:44

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