Why can I not get this simple circuit to work?

[Andrew Leigh]

I am a build by numbers guy who build the most basic of stuff as the rest has me snookered.

For some reason I cannot get this circuit to deliver less than about 10V and I need 9V. Input on the left and the diodes have the strip away from the board. This is the second time I have built the strip board from scratch (differently) with the same result?

 

[ronsimpson]

What is the input voltage?
What is the output voltage? 10V?
Is the Input-Output = 0.7V? or 3V?
What is the voltage on the "ADJ" pin?

 

[Andrew Leigh]

Input = 13.08V (Battery)
Output = 10.9V (this with the value of VR1 at 1k5 and no R2)
3V
"ADJ" pin - 10.8V

Thanks

 

[ronsimpson]

Go to **broken link removed**
Enter 110 for R1 and 900 for R2 then push calculate.
You have the pot set to 18 volts.
You need to set the variable resistor to about 900 ohms or you can double the value of your 110 ohm resistor.

 

[Andrew Leigh]

The calculator tell me that R680 over the R110 should give me 8.75V (don't have a 680 in the box so two R33o's in series).

So with R660 inserted the output measures 10.75 and at "ADJ" 7.5V now? I must have made a PC mistake?

 

[audioguru]

Many of those "calculate" programs are wrong.
The LM317 works very simply. It develops 1.25V across your 110 ohms resistor which causes a current of 1.25V/110 ohms= 11.36mA. The 1.25V will be part of the output voltage and you want an output of 9V so the pot will have 9V - 1.25V= 7.75V across it and will have 11.36mA in it then its value is 7.75V/11.36mA= 682 ohms. 680 is a standard value.

Your "pot" is 660 ohms so your output voltage should be 1.25V + (11.36mA x 660 ohms)= 8.75V.

 

[Andrew Leigh]

Agree but the output is not 8.75V and therein lays the problem, either I have fried the LM317 or I need to check the circuit which I have done numerous time and simply cannot find the problem which I am sure is simply the translation to the strip board, will have to check again.

 

[ronsimpson]

The calculator tell me that R680 over the R110 should give me 8.75V (don't have a 680 in the box so two R33o's in series).

So with R660 inserted the output measures 10.75 and at "ADJ" 7.5V now? I must have made a PC mistake?

The voltage from OUT to ADJ should be 1.25. You have 2.25V. Why?

 

[Andrew Leigh]

Just measured across OUT to ADJ and it is indeed 1.25V with the R660 / R110 resistor combo.

 

[ronsimpson]

Just measured across OUT to ADJ and it is indeed 1.25V with the R660 / R110 resistor combo.

The regulator has only one purpose in life. It tries to make 1.25 volts across OUT to ADJ.
It sends power from IN to OUT until (OUT to ADJ) is 1.25V. If the voltage is above 1.25 it stop send power.
Your job is to find resistors that give you the right voltage.

 

[Andrew Leigh]

You gave me the calculator, Audioguru confirmed it so the values are correct, I am getting the 1,25V.

I have tried from R10 and burnt my fingers to 10k and I cannot get the voltage below 10.75V

There must be a fundamental problems on the strip board, will check in about 15min.

 

[Andrew Leigh]

I hang my head in shame.

The eye loupe uncovered a poor joint on the R660 resistor, eyes not what they used to be, especially at night.

Many thanks for taking the time out to assist.

 

[ronsimpson]

eyes not what they used to be, especially at night.

It is light here. lol Same problem here even in the light.

 

[Andrew Leigh]

Off Topic.

Did business with people in Loveland, Electrom Corporation. The owners sold (they called him the Big Swede, he played steel guitar in a band), they moved to New Mexico and it is under new management.

 

[ronsimpson]

Off Topic.
Did business with people in Loveland, Electrom Corporation. The owners sold (they called him the Big Swede, he played steel guitar in a band), they moved to New Mexico and it is under new management.

Driven by many times. They do high voltage things. I like high voltage to.

 

[Andrew Leigh]

Yeah the original owner was a bit of a genius / maverick. The make high voltage impulse generators for testing electric motor windings. They use d.c. which is non destructive and they put a rather steep wave form into the windings (200us if I remember) trying to find inter turn winding faults. They have just brought out a digital version which I am told is outstanding. I was their agent in S.A. until our entire group of companies was liquidated (Chapter 11?) due to fraud by the two primary shareholders.

 

[ronsimpson]

I to know this problem.
I watches a manager get away with some money. It cost the company $20 for every $1 stolen.
It is like if a bad man brakes down you house door and takes some money. The broken door costs more than the money.

 

[Andrew Leigh]

Yeah 100% correct. Anyways going to mount the board now and then turn in. Appreciate the help and the chat.