while making a voltage regulator i followed the circuit given in the datasheet of lm317t (st electronics) for voltage regulation.
but when i set up the circuit the output voltage is not uniform.It fluctuates around 10 to 100 milli volts.
iam powering it with a 12-0-12 volt transformer.
can anyone say how to reduce the fluctuations?
Post your schematics with elements value.
i have a diode and a capacitor to the ac supply of transformer and i got a dc supply of about 17 volts.
In the schematic ,
C1 0.1 micro farad ceramic
R2 10k ohms single turn pot
R1 240 ohms
c2 1micro farad electrolytic 50 volts..
The supply from the transformer is very lumpy, you need a big capacitor (100µ - 10,000µF) in addition to C1 to smooth-out the lumps.
The supply from the transformer is very lumpy, you need a big capacitor (100µ - 10,000µF) in addition to C1 to smooth-out the lumps.
That and use at least 2 diodes for the AC-DC.
i used a 5000 micro farad capacitor onthe output.
i used two diodes for the conversion ac to dc.
What's the frequency of the fluctuations? How are you measuring them? Are you using a scope or multimeter?
If they're high frequency then are you using the low inductance ground attachment of the probe?
What load are you putting on the output? The datasheet suggests that proper regulation requires a minimum load current of about 1.25mA (basically it has to dump the current needed to operate the internals of the regulator - it does this through the output terminal.) In your circuit, the only load is the 10k feedback R1 - this is barely adequate to sink working current of the regulator. Try it with a load of at least 10mA.
Edit: Sorry, ignore that. I'd managed to interchange R1 and R2. Although, you might still have problems if R2 is too high in value - consider what happens to the LM317's operating current.
Definitely got the pins round the right way?
R1 should be 120 ohms on an LM317 to meet the minimum load requirements. For some reason, all the data sheets show sample circuits based on the LM117 which has half the minimum load requirement.
i used a 5000 micro farad capacitor onthe output.
i used two diodes for the conversion ac to dc.
Are you talking about C1 or C2?
C1 needs to be 5000uF.
I am measuring the voltage with a normal multimeter.
The capacitance C1 is 5000 micro farad.
I have tested the same circuit with a 1k resistor on the output but got the same results.sometimes voltage changes by 10 millivolts or about 0.1 volt ,its unsteady.
I have also checked the datasheet and wired the pins appropriately.
How did you connect the 10k pot
you have 3 leads for that 0 - wiper - 10k
If you connected between wiper and 10k , then you may have a high resistance between adjust and ground and get a bad voltage on the adjust then...
" The supply from the transformer is very lumpy, you need a big capacitor (100µ - 10,000µF) in addition to C1 to smooth-out the lumps."
Lumpy! I'm going to add that to ny technical vocabulary.
" The supply from the transformer is very lumpy, you need a big capacitor (100µ - 10,000µF) in addition to C1 to smooth-out the lumps."
Lumpy! I'm going to add that to ny technical vocabulary.
As long as you don't have 'GRASS' or 'floppy the banjo clown' spikes , it's ok ... lumpy is the least of your worries... floppy is a real killer
and don;t start about flicker and popcorn noise ...
Lumpy! I'm going to add that to ny technical vocabulary.
Yeah, apologies for breaking into jargon.
I have tested the same circuit with a 1k resistor on the output but got the same results.sometimes voltage changes by 10 millivolts or about 0.1 volt ,its unsteady.
Replace the pot with a resistor and see if the voltage still changes. I have seen adjustable power supplies that are correct on paper but fluctuate because of a bad quality pot.
Try to use a 10 turn version if you can, those single turn ones are generally crap for stuff like this.
If you need even more stability, put a 10uf capacitor parallel with R2 and also add a diode in parallel with R1, cathode on R1 to lm317T adj pin.
I always use 'furry' if there's HF riding over a sine wave.
Or 'Fucked' if something can't be repaired.
Also, I invented the phrase 'Different kettle of ballgames' and am trying to popularise it. Feel free to use this in general conversation.
I like "furry".
What the hell is a kettle of ballgames?
A cross between 'a different kettle of fish' and 'a whole different ballgame'.
before putting on the breadboard i soldered wires on to the lm317 pins with a 25 watt soldering iron.(tried the lm7805 with the same transformer and everything worked fine).
I want to know if lm317 device is heat sensitive (that is with a 25 watt iron)
before putting on the breadboard i soldered wires on to the lm317 pins with a 25 watt soldering iron.(tried the lm7805 with the same transformer and everything worked fine).
I want to know if lm317 device is heat sensitive (that is with a 25 watt iron)
Unlikely if its a TO-220 package because it has lot of thermal capacity. How long did you keep the iron on each pin during soldering? 2-3 seconds seems to be the limit to stay out of risk.
Post a picture of your circuit and setup so that its easy to find if anything is obviously wrong in such a simple circuit.
Regards,
Vikas