Seeing the title of LM317, I know that you may be familiar with it! You usually need an adjustable power supply! And I only have LM317, so I still have a thick face to post! Why not buy a switching power supply? Because hands-on progress, it is fun! And the switching power supply is not very familiar! Obviously, I am not a master! I hope the master can forgive me! I only want to learn from each other! I hope that one day I can climb the peak!
This is the schematic! A current-limiting protection circuit is added in front! This protection circuit is self-locking. Once the current exceeds the set value, the voltage between the emitter and collector of Q3 increases until D7 is 8.2V stable. The reverse breakdown of the diode is turned on, then Q2, Q5 will be turned on, Q5 will lower the Vbe of Q4, Q4 will be cut off, and Q3 will be cut off! Then it will protect the circuit! Because it is self-locking, so Need to disconnect the front power supply, and then turn it back on, it will return to normal! The protection circuit is much worse than the ideal state in actual operation, so I designed the maximum current value and set it small. One point! I have tested this protection circuit alone to protect it! But after adding LM317, I have not tried it! (After all, the taste of burning the circuit is not good, and... I don't want my only transformer to be extinguished! Therefore, the defect of this protection circuit is still there! For example, if you change the power supply voltage to 15V, then the protection current will also increase, then it is possible to burn the circuit! In fact, I do not want to use the resistance sampling method to detect Current! I hope each road is high People can give some advice to the younger generation. If something is wrong or what should be improved, you can help me! I need to make progress, thank you in advance!
This is the welding diagram of the hole plate: in some places, the component size relationship may be adjusted in the real object! (Note: the diode across the output of the LM317 output is added to the figure)
Add: C6 and R4 are to make Q2 stable and conductive!
Next is the physical map:
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