Lm 317T voltage regulator Circuit

[Gregory]

I have Built a basic 12 V DC circuit using a LM317T regulator but I can not get the voltage to adjust Using 500K pot.
If I apply 5 Volts to the circuit Pin 2 and 3 are the same Voltage when adjusting the POT but pin 1 has the veriable voltage.
The veriable voltage should be pin 2 Where Hav I gon wrong.
I will post a circuit of thge Voltage regutator.

 

[ericgibbs]

I have Built a basic 12 V DC circuit using a LM317T regulator but I can not get the voltage to adjust Using 500K pot.
If I apply 5 Volts to the circuit Pin 2 and 3 are the same Voltage when adjusting the POT but pin 1 has the veriable voltage.
The veriable voltage should be pin 2 Where Hav I gon wrong.
I will post a circuit of thge Voltage regutator.

Hi,
You have a resistor missing either a 120R or 240R, also the 500K pot is about 100 times times higher than needed.

For 12Vout you need at least 15V input, always have the input at least 3V higher than the required output voltage

 

[Ian Rogers]

Heres the circuit from the 317 pdf...

View attachment 66784

Notice the adjustment is relative to the output..

 

[Ian Rogers]

No fair Eric..... Too fast...

 

[atferrari]

No fair Eric..... Too fast...

Hola Eric,

How many hours per day you stay around?

Impressive!

Hola Ian!

 

[4pyros]

I have Built a basic 12 V DC circuit using a LM317T regulator

If I apply 5 Volts to the circuit Pin 2 and 3 are the same Voltage

You cant get more out than you put in!!

 

[audioguru]

Heres the circuit from the 317 pdf...

View attachment 66784

That is the circuit for the more expensive LM117 where R1 can be 240 ohms.
The LM317 uses 120 ohms for R1 then the value of the pot should be 2.5k.
If an LM317 uses 240 ohms for R1 then some of them will have an output voltage too high when there is no load.

 

[Ian Rogers]

That is the circuit for the more expensive LM117

Missed that... It WAS the LM317 pdf I was viewing.... It must cater for both....

Sorry Gregory....

 

[Mr RB]

Modern LM317 are generally good with the 240 ohm resistor, I think they are a bit better than the original 40yr old parts.

Also, you should ALWAYS add the critical cap between the adjust pin and gnd! Unfortunately not shown on all datasheets. In the event of a microscopic break in conduction of the pot wiper when the pot is turned (ie pot "crackle" caused by corrosion and dust) if there is no cap the LM317 will sense that Vout-Adj has dropped to zero and will turn full on, basically it becomes an amplifier with almost infinity gain and will provide full PSU to the output! Even if that is just for a few uS it's a very bad situation.

 

[Gregory]

I have added a nother Circuit to the LM 317 which is working now I placed the Resistor in the circuit.260 ohm Resistor.
The Circuit I have added is a High Current with the Regulated Voltage I have tested the circuit with 30 V DC Input.
I am getting 27 Volts out of the voltage regulated circuit and adjusting the 5K pot down to the lowest reading I get .750 Volts
When I place the digital metre into the High Current circuit at 30 Volts DC input into the circuit I get a Reading of 10.3 volts and adjusting the pot to the lowest reading I get 2.7Volts.
I have combined 2 circuits together.
The circuit I used for the High current is on the net but have changed the circuit.
http://www.reuk.co.uk/High-Current-Voltage-Regulation.htm
I am looking for 27Volts out at 12 AMP to drive a led light with 200 leds in the unit.I am using a DC battery to get the required power.
I will post photoes of the unit
Hope you can help me.

I the last photo you will see I have added a resistor and the brown wirer
This may help you to see under the resistor and wirer
I have not loaded the Circuit up at this stage.
If you require a photo of the solder side of the circuit board I can provide that

 

[audioguru]

I have added a nother Circuit to the LM 317 which is working now

It has poor voltage regulation when the load current changes. Since the transistors are just simply emitter-followers their output voltage drops when the load current increases.

The datasheet for the LM317 (and for the LM7812) shows a PNP transistor at the input that has feedback to the LM317 so the voltage regulation is perfect. The PNP transistor can drive many NPN transistors for very high output current with good voltage regulation.

 

[Gregory]

Do I Discard the above project and start again
What Is ment Improve ripple Rejection on you circuit Digram ( is it relating to the Caps in the Circuit or adding more

 

[Gregory]

Can I use the existing Voltage regulator that I have Built

 

[Mr RB]

What is your battery voltage?

The circuit Audioguru suggested is a much better regulator, so that would be advisable if you are using a battery as the battery voltage will vary. I think you could keep your PCB and the power components and modify it, but a far ebtter idea would be to use a decent heatsink for a start and put your power components on the heatsink then design and build the circuit around that. It may not need a PCB as the main power parts are physically mounted on the heatsink and you don't need much more than a LM317 and a few discretes which can be wired point to point to the power transistor legs.

Before rebuilding it would be good to outline what the battery is, what the usage is for etc and people can suggest the best options of what circuit to use and how to construct it.

 

[Gregory]

The Battery is Powerizer 37V - 6.4Ah 30 A
Li-ion Polymer Battery Pack
Can I use in the LM 195s a TO2 body

 

[audioguru]

National Semi show the circuit with LM195 power darlington transistors because they provide overload protection and they make them. You can use any power darlington transistor like the TIP110 or TIP120 but if the output is shorted then there is no protection (lots of smoke).

 

[Gregory]

The only Darlington NPN Transistor that I could buy from the locat Tandy outlet where I live is
BD681 NPN To 126
and the equivelent to the 2N2905 Is 2N2907 whichI think Is a PNP Transistor To 92 Body
Well the components do the Job

 

[aljamri]

Also, you should ALWAYS add the critical cap between the adjust pin and gnd! .

which one of the attached ? 10η or 10μ ?

I'm using LM317 to get 1.5v to 6 volts output ( Variable ) using 9v input and the 5k Pot.

 

[audioguru]

The only Darlington NPN Transistor that I could buy from the locat Tandy outlet where I live is
BD681 NPN To 126
and the equivelent to the 2N2905 Is 2N2907 whichI think Is a PNP Transistor To 92 Body
Well the components do the Job

The circuit in the datasheet is extremely old since it uses obsolete 2N2905 or 2N2907 transistors. Use an available modern transistor instead.

Tandy is gone from Canada since they ripped off too many people with RadioShack garbage.

There are THOUSANDS of NPN darlington transistors and little PNP transistors available in North America.

 

[Gregory]

Can the test you do to find out B C M and NPN on a Dartlington transistor can you use a DMM
Where the reading between the base and collector is the lowest reading on diod test
And the NPN the N is the negative and P is the positive of the DMM
Is this correct