For a project I need to make a circuit to produce a stable 5V output. The input range is 5V to 15V. Im using the LM7805 as it seems most logical, but when the input is less than 7V the output drops below the desired 5V. For 5V input the output is 3.5V. How can I fix this? I tried checking the datasheet to add the right amount of capicators as seen below, but it does not give any other result.

Any ideas?

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  • 6
    \$\begingroup\$ "I need to make a circuit to produce a stable 5V output. The input range is 5V to 15V. " Even LDO linear regulators need some voltage margin from the input. Search for "dropout voltage" at the datasheet. Anything below 7V at the input is outside the specs. \$\endgroup\$
    – devnull
    Nov 3, 2021 at 22:25
  • \$\begingroup\$ Any ideas for another circuit to reduce input voltage to 5V? \$\endgroup\$
    – BazookaBan
    Nov 3, 2021 at 22:54
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    \$\begingroup\$ Also check the current consumption of your project. That can be a limitation for selecting the correct regulator and designing the power supply. Using an LDO (low dropout voltage regulator), the power dissipation is P = (Input voltage - Output voltage)*Output current E.g. 15V for input and 5V, 50mA output will dissipate 0.5W heat! \$\endgroup\$
    – Horv
    Nov 3, 2021 at 23:10

1 Answer 1


The LM78xx series of voltage regulator have dropout voltages of 1.5 to 2 volts. All linear regulators have at least some dropout voltages, which restricts them to always having output voltages lower than their inputs.

If you can always input a higher voltage than your desired output voltage, but not by much, then you may be able to use a low dropout voltage regulator -- but it's up to you to go looking for a suitable one.

If you really need no voltage drop at all at the minimum input voltage, then you probably need a buck-boost switching regulator.


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