High Current

[chandu13]

Hi

I required 12V 3A. For this one iam using L7812 CT (TO-3)

But this component is not working properly.

I have 12V, 1A (L7812CV) Regulator, this is working well.

Can I use L7812CV for 3A load applications?

Please suggest me how to use 1A regulator for 3A load applications.

I have TIP122 transistor, please provide me circuit-using TIP122 .

Regards

chandu

 

[Papabravo]

In general you can't make a part designed for 1A handle a 3A load. I suppose you could have three of them in parallel with their outputs combined by diodes.

After that you lost me. What is the connection between the 7812 regulator and a TIP122. They are different animals.

 

[ericgibbs]

Hi

I required 12V 3A. For this one iam using L7812 CT (TO-3)

But this component is not working properly.

I have 12V, 1A (L7812CV) Regulator, this is working well.

Can I use L7812CV for 3A load applications?

Please suggest me how to use 1A regulator for 3A load applications.

I have TIP122 transistor, please provide me circuit-using TIP122.



Regards

chandu

Did you want to use a bypass transistor with 7812?


Eric

 

[Papabravo]

With 0.5A going through R1, that is 0.25 watts per ohm. Isn't R1 going to get kinda toasty?

 

[chandu13]

Thanks for reply

It is better to use three 7412 regulators Parallel

Iam getting confusion to arrange the regulators and Diodes in Parallel

Please can you provide circuit diagram

Regards

chandu

 

[blueroomelectronics]

What source voltage are you using? Why not just replace the defective 7812CT? Do you have the required caps in your circuit?

 

[ericgibbs]

With 0.5A going through R1, that is 0.25 watts per ohm. Isn't R1 going to get kinda toasty?

hi,
Woops,,, of course you are right, he would get the 'dark brown' smell.

Thats the trouble with these 'green' solar powered calculators, just as you hit the equals key, the Sun goes in!

A 0.5W or 1W rating would be the right choice.

Eric
Thanks

 

[Papabravo]

Take the output of a regulator to the anode of a diode. Connect all the cathodes together. The output of a 7812 is now 11.3 Volts for silicon diodes or 11.7 for Schottky diodes. So if you use adjustable regulators and boost the input a bit to compensate you can get 12V out.

 

[audioguru]

The resistor has 0.8V across it and 0.5A through it. Then it dissipate only 400mW.

If you connect regulators in parallel then the one with the highest voltage takes about 1.2A and current-limits and drops the voltage down until the one with the next-lowest voltage begins to conduct. Then the voltage regulation is lousy.

 

[Papabravo]

The resistor has 0.8V across it and 0.5A through it. Then it dissipate only 400mW.

If you connect regulators in parallel then the one with the highest voltage takes about 1.2A and current-limits and drops the voltage down until the one with the next-lowest voltage begins to conduct. Then the voltage regulation is lousy.

So the half-watt would be marginally OK but the 1 Watt would be better.

I didn't say parallel regulators combined with diodes was a good idea, it just answers the original question which was "is there any way to use 1A parts for a 3A application.". As you quite rightly point out the performance is ...ah...sub-optimal.

 

[mcs51mc]

Still need some schematics?
Here are two:
one for 24Vdc/8A
one for 12Vdc/1.7A

I think you can adjust the last one to 3A by adjusting current feed back resistance. A 2N3055 can deliver up to 8A with proper heat sink of course.
You can also use the 8A principle to deliver max 3A in the 12V one.
Your choice

 

[hotwaterwizard]

What about the LM350K ?
It is 3 amps TO3 case.
Adjustable but you can make a circuit for steady 12v output.

 

[hotwaterwizard]

Here is a Handy circuit for 5 amps.
Use a LARGE Heat sink for High Current.

 

[Oznog]

Regulators CANNOT be put in parallel to increase their rating. One will usually end up taking all the current.

What is your source voltage? There are a lot of thermal issues if you have say a 20V source. That would be 24W of heat!

You can always use an external transistor to create an emitter-follower circuit. The output will be 0.5v-1v less than the regulator's voltage. Yes the voltage will change a bit with load.

You can use an adjustable reg to start with 13v or whatever to get the nominal 12v you need. But then if you've got an adjustable reg like the LM317T, there's an "adjust" pin for feedback. Instead of dividing the 317's voltage output and feeding back to that pin, why not divide your big external transistor's output voltage?

But anyways there ARE bigger regs, this one handles 5 amps:
**broken link removed**

But again pay CLOSE attention to its heat dissipation with the heatsink you have vs how much wattage your application will generate.

 

[hotwaterwizard]

Regulators CANNOT be put in parallel to increase their rating. One will usually end up taking all the current..

Hmmmm, If this is completely true explain these Articles.

**broken link removed**

**broken link removed**

**broken link removed**
**broken link removed**

https://www.electro-tech-online.com/custompdfs/2007/08/434875f1.pdf
https://www.electro-tech-online.com/custompdfs/2007/08/434875f2.pdf

https://www.electro-tech-online.com/custompdfs/2007/08/72204di.pdf

 

[hotwaterwizard]

Regulators CANNOT be put in parallel to increase their rating. One will usually end up taking all the current.

Hmmm, If this is completely true explaine these articles.

**broken link removed**

**broken link removed**

https://www.electro-tech-online.com/custompdfs/2007/08/72204di-1.pdf

 

[audioguru]

The article says that current sharing is poor unless resistors or diodes are added in series with the outputs of the regulators. The article says that current-sharing resistors cause a voltage drop of 1.5V at full load so the excellent voltage regulation of the ICs is ruined.

 

[Hero999]

I'd just stick them in parallel (without any series resistors) if I were you.

Most voltage regulators lower the voltage and are protected from thermal run-away. For small loads the strongest regulator will source all the current, as the load current increases it will start to shut down and the slightly weaker regulators will provide the current.

 

[mneary]

I'd be concerned about the long term reliability of a regulator constantly in thermal limiting mode. If it's for hobby, might be OK - just keep curious fingers off the hot surfaces (they'll be around 100c). It's certainly expedient if you're just building one of them.

You might encounter stability problems which will be highly annoying if you don't have the skills to troubleshoot and fix.

Over the long term, you'll learn to design a proper power supply with an adequate heat sink. It might not be necessary to do it now.

 

[mvs sarma]

Hi Chandu,
did you really go thro the applications of 7812 fir high current with short circuit protection -- these are well described in the datasheet also. First priority if can source is LM350(TO3) as suggested by Hotwaterwizard-

if 7812 is preferred to be used, try to follw the high current application.
It is better not to go for paralleled regulators-drawbacks indicated by AudioGURU- and land into complication and non-comletion of the project.

Sarma