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.
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.
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.
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.
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
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.
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.
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.
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.
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.