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I am using 7805 and 7815 for the voltage 5 V and 15 V respectively. I provide 24 V to 7815 it is giveinng me output voltage 18.5 V instead of 15 V. According to 18.5 V to input to 7805, its output is 6 V. It should have to provide 5 V output. similarly, the output of 7815 should be 15 V.

I don't know what is happening. Can you tell me what will be the error in the circuit?

enter image description here

I am using this schematic in hardware.

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    \$\begingroup\$ With no load the regulators will find it hard to regulate. Connect it to a simple resistive load (say a 1KΩ resistor) and measure the voltage then. \$\endgroup\$
    – Majenko
    Commented Aug 12, 2016 at 18:53
  • \$\begingroup\$ That doesn't really qualify as a full schematic. "Can you tell me what will be the error in the circuit?" Not with the little information you gave. \$\endgroup\$
    – Transistor
    Commented Aug 12, 2016 at 18:58
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    \$\begingroup\$ @Jim Until the pot catches fire as you hit the last few mm of track... ;) \$\endgroup\$
    – Majenko
    Commented Aug 12, 2016 at 18:58
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    \$\begingroup\$ I've seen a 7905 give too high an output without a load, but never a 7805. Not sure what that means. \$\endgroup\$
    – Robert Endl
    Commented Aug 12, 2016 at 19:18
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    \$\begingroup\$ Is it possible that your meter is off? A 1 volt error at 5 volts and a 3.5 volt error at 15 volts suggest this possibility. \$\endgroup\$
    – Barry
    Commented Aug 12, 2016 at 19:20

3 Answers 3

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You need a minimum load for them to regulate. Add a resistor to give 100 uA of load and the situation should improve.

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Your circuit is fine. The battery in your meter needs to be replaced.

The voltmeter is reading high by more than 20% because the internal voltage reference has gone out of regulation (low) and the readings are a ratio like Reading = K * Vin/Vref.

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    \$\begingroup\$ If OP accepts this you will earn +1 for mindreading. \$\endgroup\$
    – The Photon
    Commented Aug 12, 2016 at 20:06
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I know this is dead but I had the exact same issue. Turns out I had the chip backwards. L7805cv

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