For a 12 V regulator, you can use the formula here: http://www.ti.com/lit/ds/symlink/lm317.pdf#page=10

Probably 1% resistors would give a more accurate value or just use the POT.

 

Thanks, sorry to be a complete noob but what formula? Completely lacking in the mathematical understanding lol

 

For example, a 1K R2 resistor, and the 240R R1.
Vref = 1.25V. This is the voltage between the Output and the Adjust pins.

Vo= 1.25(1+1000/240)
Vo = 1.25(1+4.1667)
Vo = 1.25 * 5.1667

Vo = about 6.468V

Or you could use.... http://www.reuk.co.uk/wordpress/electric-circuit/lm317-voltage-calculator/

 

thanks for that!

Would i still need to use Caps with this circuit?

 

thanks for that!

Would i still need to use Caps with this circuit?

It is always a good idea to use the caps as it stops the regulator oscillating.

 

how do i work out what Cadj value should be?

 

I'd use a 10uF tantalum cap. And have an extra 100uF 35V cap on the input too as well as the 0.1uF s the main filter caps will be quite a way from the regulator.
And add the diodes as shown. they can be any 1N400x diodes you can get.
The more bullet proof you can make it the better.

 

Another option is i have this lying around also:
View attachment 135765

You should be careful with thisone not to burn the house if it overheats!

 

You should be careful with thisone not to burn the house if it overheats![/QUOT

That good is it!!?

 

So I got around to making this today and I’m not very impressed....

The reading is erratic and the adjustment is far too sensitive.

Any ideas as to the problems?

I have a video clip but not sure how to upload due to size of file?

 

Any ideas as to the problems?

Now without seeing a schematic of the exact circuit you built.

 

View attachment 135833

VR1 is actually 5K

 

 

Video of it working, climbs on its own and jumps all over the place.

 

What is the value of your test load resistor.?

 

The resistor is 100ohm and the pot is 5k

 

Not the components, , the actual load resistor the LM317 is driving.? Connected across Co cap?

 

I don’t have one as that’s not the schematic I worked too......

 

 

The 5K pot and the 100R together are not the correct ratio.
As an exercise, run those values through the voltage calculation to see what you will get.
No wonder it is hard to adjust. You do need to select the resistors to suit your application. Most of the adjustment with the values you have will be the reg trying to output more volts than the supply.
It may be oscillating too so I'd recommend adding the CAdj and D2.
How does it look if you set the output to 5V? or even 1.25V? Is is stable?