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Hi everyone. I am trying to make 12VAC - 5VDC power supply. However when plugged in, voltage between L7805CV in - ground was 4V while output was 1V.

I have test 7805 separately and it works correctly though. The rectifier and filter without 7805 also work correctly.

What was possibly wrong here?

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    \$\begingroup\$ What was possibly wrong here? - something else. \$\endgroup\$
    – Andy aka
    Commented Oct 14, 2020 at 13:05
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    \$\begingroup\$ Check the AC input to the bridge. Measure the DC output of the bridge. It should be almost \$ \sqrt 2 V_{AC} \$. \$\endgroup\$
    – Transistor
    Commented Oct 14, 2020 at 13:24
  • \$\begingroup\$ Maybe you hooked the bridge output backwards. The circuit you show should work, so either it's not actually what you say it is, or something is defective. \$\endgroup\$
    – Spehro Pefhany
    Commented Oct 14, 2020 at 13:43
  • \$\begingroup\$ Did you measure the 4V/1V with or without a load connected to the regulated 5V output? \$\endgroup\$
    – ocrdu
    Commented Oct 14, 2020 at 14:07
  • \$\begingroup\$ @Transistor, ocrdu I will reply for you guys tomorrow, but thanks for suggestion ^^. \$\endgroup\$
    – Tan Nguyen
    Commented Oct 14, 2020 at 15:35

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