Connecting Voltage Regulators 78XX in Parallel for Higher Combined Current Output

Voltage regulator chips mostly have their maximum current output specs fixed to some predetermined levels. Increasing them to a higher level would normally call for external out board transistors and complicated associated circuitry which might be difficult to configure for the new hobbyists. Putting a few of them in parallel, possibly solves the problem.

The idea was requested by Mr.Raja.

Sir,
could i use three L 7815 voltage regulator ic in parallel, to get 15 volt 4 amps dc current from about 20 volt 5 amp dc source?

Sir, as LM 338 and their equivalent ic s ( which gives 5 amps ) are not available in my town. I planned to use three 7815 in parallel. Is my idea works? If so please help me.
How can i connect them in parallel ? Could i connect input of all three 7815 ic by a common wire or i should separate mutually by a diode of 2 amp? And what about out put, should i separate them or use
a common wire? And i think, i can connect the negative terminal of ic with a common wire. Is it? Please guide me.

Solution:

Although not recommended by many, the issue can be handled simply by connecting the regulators in parallel, as shown in the following diagram.

Here we can see the terminals of the all the three ICs connected in parallel except the output pins which are terminated with individual diodes.

However the above connection might face a crucial drawback. Since all the ICs wouldn't have precisely identical characteristics and specs could vary with their current limits, and ultimately lead to one of them supplying greater amount of current than the other, and overheating in the course.

Although this won't pose a threat to the ICs as these are always thermally protected from inside, it's never a good idea to have a semiconductor device sizzle unnecessarily.

The issue can be very easily tackled by connecting the counterparts over a common heatsink, as shown in the diagram below.

Since the tab for the ICs connect with their identical common leads (ground lead), doesn't need any sort of isolation in the form of mica isolation kit etc.

Just get them on-board over a common aluminium plate and now you can relax as the heat dissipation across the plate would result in correct transition of heat enabling each one with an equal share of current at their respective outputs which in return would result in an optimally combined higher current outputs, as required.

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