Doubling 7805 current capacity?

To get a higher voltage regulation current, is it OK to parallel 2 7805 voltage regulators? So if one 7805 can handle 500ma, can I parallel 2 7805's to get 1000ma current capacity?

By parallel, I mean to connect the +5V outputs together, and GND together.

Thanks !

Hi!

No problem. Also, put a big heatsink on them.

Charliez, I suggest looking at the 7805 datasheet. I believe I remember seeing a suggested circuit for running multiple regulators in this fasion, and it wasn't quite as simple as running in parallel. Just a suggestion.

also, there are 1, 1.5, 3, 5 etc amp regulators that you can use, which will regulate +5V, maybe this is a simpler solution?

Finally, the 7805 datasheet should have a suggested circuit for creating a pass transistor circuit to increace the output current.

Just things to look at...

Hi Charlie,
A regular 7805 will supply more than 1A if you don't let it get too hot and not exceed 15V across it. Maybe you are using the 78M05 that current-limits at 500mA. See the datasheets.
Paralleling is not recommended. If you parallel them, then there will be an abrupt drop in their output voltage when the higher-voltage one (they probably won't be the same) current-limits at its rating and the output voltage drops down to where the lower-voltage one begins to share the load current.
The datasheets show how a PNP power transistor can be added to handle much more current. A second transistor can be added for current-limiting or just let the 7805 go into thermal shutdown (because of a small heatsink) then it will also limit the current in the PNP.

You CANNOT directly place three-terminal regulators in parallel for a higher current output. Regulators have a voltage tolerance (±0.1v is not unusual) and no two regulators regulate at exactly the same voltage. If you place two directly in parallel and one regulates at a voltage that is 0.05v more than the other, this regulator will do all it can to bring the output voltage up to what it wants while the other sees the higher voltage at the output and shuts down, leaving all the current load on the first device.

One way around this problem is to parallel the chips' input and ground, but place a low-value (e.g., 0.1 ohm) resistor in series with each output terminal before connecting them together at the other end of the added resistors. This will provide a resistance for the small difference in regulation voltage between the two at the sacrifice of making the supply just a wee bit "softer", i.e., not being able to regulate as tightly as a single chip. Usually this is not a big problem in most applications.

Checking out the 7805 data sheet will show methods of using extra parts around the regulator for extra current capacity. Also, the TO-3 7805K package will handle 1.5 amps when properly heat sinked.

Don't forget that the higher your raw dc voltage to the chip, the more it will dissipate, so keep the raw dc to a just above the necessary headroom for best regulation, especially on higher current supplies.

Dean

Don't parallel them, for the reasons listed above. And why? A 7805 can handle 1 amp, there are ones which can handle 1.5 amps. You must always properly heatsink it based on the heat generated by the voltage drop and current involved.

There are other regs out there which can handle higher currents still.

There are other regs out there which can handle higher currents still.

Click to expand...

yeah like the LM138/LM338 with their 5A output capability

but they are expensive than the 7805. but if u add up two 7805s and the resistors, u will be better off with a single regulator that can handle more current

Thanks all for the replies. I'll check out the data sheet. Seems using a higher current rated regulator is the simplest thing to do.

Cheers!