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78L05 regulator output = 8V ?!

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sayfollah

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78l05 à 8v

I switched from using the regular 7805 regulator to the small one 78L05

The problem is that the output of 78L05 Vout = Vin - 1V ; when the input is 9V battery the output is 8V approx.

I tried more than 20 pieces of 78L05 and all are giving the same output .

I experiment them without connecting them to any other parts . Is there a solution for this problem , or they are all damaged ?
 

Pld4me

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78l05 capacitor

Try them in a circuit with a load of at least 1mA.

I believe they have to be loaded.

Regards,

Pld4me
 

cancel

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78l05 problem

they do not need to be loaded afaik, did you use correct pinout??
 

    sayfollah

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rfmw

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7805 8v

Right, if you used TO-220 package for 78xx and are now using 78Lxx in TO-92, then the pins are reversed... 1 2 3 = In Gnd Out for 78xx and 1 2 3 = Out Gnd In for 78Lxx.

Happened to me once also ;)
 

    sayfollah

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sayfollah

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7805 78l05

Thanx for your help ..

rfmw , that works .

I had connected it reversed , even though I checked the 78L05 datasheet twice :) . I am feeling myself clumsy .

Thank you for your help .
 

eanic

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how to damage 78l05

idea 7805 adj Volt output.
for 78L05(to-92) = 7805(to-220)

https://circuit-electronic.blogspot.com/2007/03/power-supply-5-22v-by-7805.html
04-03.jpg
 

banjo

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78l05 to-220

The reason that your output was 8V when you reversed the input and output of the regulator was due to an internal diode included within this IC. The diode is connected with the anode on the output and the cathode on the input. Its purpose is to discharge the output capacitor at power off. If the output capacitor holds a charge longer than the input capacitor, it can reverse bias the internal pass transistor and damage it.
When you connected the regulator with the input and output reversed, this diode was then forward biased which increased the output voltage .

I mention all this, because this sort of voltage reading is a valuable troubleshooting clue. If the output is too high and the device is not shorted, then I usually suspect an improperly installed linear regulator.
 

ttrr2000

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output 8v

Try them in a circuit with a load of at least 1mA.

I believe they have to be loaded.

Regards,

I AGREE!
 

yaqoob

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78l05 connections

never
i am using this 7805 in every day
some times i did not get correct voltage because of faulty component
please put a capacitor in the output
u will get proper voltage
 

hamdard

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78l05 linear regulator circuit

This IC is reliable, you must have taken reversed connections. Just check the connections.
 

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