High current VR

[ramotnarg]

The circuit shown here ( ) is a high current voltage regulator. I built it to power six or more ultravoilet LEDs. The LEDs need 9 volts and about 1 amp each so they can operate.

I am using a computer power supply to provide 12 volts for the input of the circuit so I can get the 9 volt output. I am using only one transister at the moment which should allow the circuit to handle 8 Amps.

I was not able to get the 4.7K variable resister so I used the only one I could get which is a 5K.

When I hook up the circuit it was able to power a small fan but I could not reduce the voltage to the 9 volts I need.

Any suggestions on why this is happening ? . Thanks in advance for your help.

 

[Harald Kapp]

Welcome to electronicspoint.

Did you take the circuit from this website? Read the posts carefully: it is said that this circuit doesn't work.
And I can't see how it should work.
Chapter 9.3.13 in the datasheet of the LM317 shows how it should be done.

The LEDs need 9 volts and about 1 amp each so they can operate.

Do these LEDs really operate from a 9 V supply? That is, do they have an integrated current limiter?
Typically LEDs are defined by the operating current, which needs to be controlled, and a variable voltage drop (depending on e.g. current, temperature, age etc.). See our resource.
In that case, a voltage regulator is not suitable for operating the LEDs. You will need a current source (possibly an adjustable one). The LM319 can be used for this, too, see chapter 9.3.3. in the datasheet.

Also note that the LM317 has a minimum load current of 10 mA (max.) to maintain regulation (chapter 7.5 of the datasheet). You may have to add an additional load resistor to force this min. current to obtain stable and correct regulation of the output voltage.

 

[(*steve*)]

If you have transistors in parallel they need emitter resistors. That's just one error in that circuit, there must be others or Harald would have highlighted this

 

[Harald Kapp]

Harald would have highlighted this

You put a lot of trust in me, thanks
In fact this circuit looked suspicious from the start and after finding that website which states that the circuit doesn't work, I didn't bother to analyze the circuit in detail.
I saw no need to do it, since there are working circuits described in the datasheet.