using regulator ic317 in voltage stabiliser

[saurabh agarwal]

hello.

we used an IC317 in Voltage regulator, and we used many components for the safety of regulator as diode in series, 100nf/250v on Capacitor, .33/275 on LT. after using all still IC317 getting open.

so what should we do, please suggest.

 

[ronsimpson]

Can you send a schematic? It is hard to understand you words.
IC317? Are you using a LM317?
Please measure voltages?

 

[saurabh agarwal]

sir, i m not so techniqal, but still asked your query to my concerned.

we are using LT Voltage of 12V to 30V
after making the DC we used an capacitor of 100nf/250V.
on LT we have used an capacitor of .33/275 just parallel to it,

on high voltage DC we have an IN4007 to its negative, and on regulator LM317 positive used IN4007 positive.

 

[ronsimpson]

What is "LT"?
Does the LM317 get hot before it "getting open".
What is the load? light bulb? radio? resistor?
What is the output voltage you want?

 

[audioguru]

Why are you using capacitors with such a high voltage rating?
The datasheet for the more expensive LM117 shows a 240 ohm resistor from its output to its ADJ pin. The LM317 needs the resistor to be 120 ohms.
The input and output capacitors must be mounted very close to the regulator input pin, output pin and circuit ground.

Please attach your schematic showing the input voltage and load resistance.

 

[saurabh agarwal]

What is "LT"?
Does the LM317 get hot before it "getting open".
What is the load? light bulb? radio? resistor?
What is the output voltage you want?

Yes sir it get hot and load is of miniature relays. Output voltage we want 12V. And the total load of all 4 relays is just 400ma.

 

[ronsimpson]

we are using LT Voltage of 12V to 30V

You can not have 12 volts out if the input is 12 volts.

And the total load of all 4 relays is just 400ma.

If the input is 30V and the output is 12V the voltage across the part is 18V. 400mA X 18V = 7.2 watts. The part you are using needs a heat sink to take the heat away. It will burn up at 2 watts and above!

 

[saurabh agarwal]

Sir we have already places an heat sink on 317.

 

[saurabh agarwal]

Sir we have already places an heat sink on 317.

 

[audioguru]

A real LM317 has "thermal protection" that turns it off when it gets too hot then it begins working again after cooling. If you have a fake one or a poor Chinese copy of one then maybe it does not have thermal protection.
You should not let the thermal protection turn it off too many times because then the chip might be fractured by the heating expansions and cooling contractions.

The datasheet shows that when its output is 12V then its minimum input is 14V or 15V but its spec's are guaranteed when its minimum input is 5V higher than its output voltage. If you are feeding its input with rectified AC then the main filter capacitor must be large enough to keep the minimum voltage a few volts higher than the output voltage.

Why do you use a voltage regulator to power relays instead of using resistors?
Why don't you post your schematic?

 

[Mosaic]

Why are you using capacitors with such a high voltage rating?
The datasheet for the more expensive LM117 shows a 240 ohm resistor from its output to its ADJ pin. The LM317 needs the resistor to be 120 ohms.
The input and output capacitors must be mounted very close to the regulator input pin, output pin and circuit ground.

Please attach your schematic showing the input voltage and load resistance.

Actually the 120 Ohm is ONLY needed IF you don't have a min. 10mA overall load on the LM317. I use 270 ohms Adj. in a standard circuit to get 12 from 36V, but I have fixed down stream loads on the LM317.

 

[audioguru]

Actually the 120 Ohm is ONLY needed IF you don't have a min. 10mA overall load on the LM317.

Many people build the voltage regulator circuit by itself without a load then they measure the voltage and find that it is too high (because there is not enough load current). Or maybe they use the LM317 regulator to power a VERY low current Cmos circuit and the output voltage goes too high and blows up the Cmos circuit. The 120 ohm resistor makes certain that the regulator ALWAYS regulates.

 

[Mosaic]

When dropping large voltages, (24V in my case). Knocking off 5 or 6mA of non essential loading adds up to offsetting 144 mW of heating. Helps a bit when cooling it.

 

[Mosaic]

I found this to be useful for LM317 design and lower noise supplies.
http://www.acoustica.org.uk/t/3pin_reg_notes1.html
Nothing new to AG i'm sure.

 

[audioguru]

The notes about the LM317 show one of the many circuits in the datasheet using the more expensive LM117 and its 240 ohm resistor.