[SOLVED] LM317 output not 3V after 7805 regulator.

[WhyWhy]

Hi Guys,

i started to build my own voltage regulator with difference voltage as 9V,6V,5V and 3V.

So, I have one 9V adapter and connected it to the 7806 voltage regulator which gets the output 6V. From the output of 7806, i connect it to the 7805 Voltage regulator which gets the output 5V. Then i connect the output of the 7805 voltage regulator to the LM317 which output gets only around 0.7V.

However, i tried connect the 9V directly to the LM317 circuit. It worked fine as the output reading is 2.97V.

The voltage regulator circuit used shown below.



Regards,
YY

 

[Audioguru]

The datasheet for the 7805 shows a minimum input of 7V. Your output current must be very low for it to work with only 6V.
The datasheet for the LM317 has all its specs with Vin - Vout a minimum of 3V but you have only 2V.

 

[WhyWhy]

But i get the output from the 7805 voltage regulator was 4.85V. By right, it should be no problem right?

 

[Borber]

Do not concatenate regulators in a chain. Input of each regulator should be connected to 9V adapter. While adapter voltage is greater than 11V your 9V regulator will have correct output.

 

[crutschow]

But i get the output from the 7805 voltage regulator was 4.85V. By right, it should be no problem right?

Not necessarily. Have you tried it with he maximum load?

 

[WhyWhy]

Borber
I tried the way like that before, it's works fine. But is it an ideal way ?

crutschow
i tried to connect it directly from 9V adapter, it's works fine with the output around 3V.

 

[Borber]

Borber
I tried the way like that before, it's works fine. But is it an ideal way ?

crutschow
i tried to connect it directly from 9V adapter, it's works fine with the output around 3V.

Dont you see the ideal way?

 

[Audioguru]

The datasheet for the LM317 lists its spec's with the input voltage AT LEAST 3V higher than its output voltage. Then yours must have an input voltage AT LEAST 6V, not 4.85V.