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The circuit consists of a STM32F030 and several 5 V relays, which are connected to the coil to open the door. The input voltage is from 18 V which is fed from a 220 to 18 V transformer (not switching transformer). When the relay is activated for 0.5 seconds, it activates the solenoid Lock, and at this time, the input voltage drops and the micro hangs. The micro watchdog is active, but it activates the micro LED that is connected to the micro. It is unwanted. The board works normally in typical without coil. I used a diode bridge circuit and a 2200 uF capacitor for the input, and the circuit is stabilized, but it still hangs sometimes. LM2596-5V switching circuit for 5 V and 3.3 V regulator is also AMS1117. Is it useful if I make the regulator linear like 7805?

Schemactics

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    \$\begingroup\$ Please post a schematic. \$\endgroup\$
    – winny
    Commented Jul 4 at 9:53
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    \$\begingroup\$ No, embed it into your question. \$\endgroup\$
    – winny
    Commented Jul 4 at 11:13
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    \$\begingroup\$ Please take the Tour and check out electronics.stackexchange.com/help/asking. Off-site links other than datasheets makes the question difficult for the reader. Please EMBED your schematic as an image or draw it using the built in tool by clicking Edit and then on the schematic symbol \$\endgroup\$
    – winny
    Commented Jul 4 at 11:19
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    \$\begingroup\$ Could be layout too. Do you have a ground plane? How many PCB layers? What happens if you just add more ceramic capacitors to all Vcc (5 and 3.3 V) pins and ground? \$\endgroup\$
    – winny
    Commented Jul 4 at 11:59
  • \$\begingroup\$ Why use such a high input voltage if you only need 5 V for your circuit? \$\endgroup\$
    – Finbarr
    Commented Jul 4 at 12:01

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