Replacing the Arduino voltage regulator

Question

I want to replace the onboard AMS1117-5.0 (broken) with a LM7805. However, the pinout is different between the two voltage regulators; AMS1117: Gnd, Vout, Vin vs LM7805: Vin, Gnd, Vout.

I would like to know what is the best practice of how to approach this? Line-up the Vin and cross the Vout and Ground pins and add some insulation so they dont make contact. How do the experts at EESX do this?

Follow-up: adding the lm7805 using jumper wires works fine with the 12v DC input i have. It is a temporary fix until replacement ams1117 arrive.

Answer 1

Why do you need to change over to a 7805? If you're gonna be bending pins up and using jumper wires, you're cruisin' for a bruisin'. A quick look at the data sheets leads me to believe there is no good reason to switch, other than the possibility that this is all you've got on hand?

If it must be done, here's how I'd do it: bend the large ground tab so that the LDO will sit at a large incline off the plane of the board. Tack it on, then solder your jumper wires from the pads to the appropriate connections.

I do not recommend doing this, just sample a replacement part. You'll get it for free, and have the satisfaction of a job well done.

Answer 2

The two devices may not be interchangeable in the target circuit (not shown). The drop-out voltage for the AMS1117-5.0 is typically only 1.1V at a load current of 0.8 amps. The LM7805 drop-out voltage is specified as typically 2V at 1A load current. You may not find the replacement works correctly.

I think you need to justify the replacement.

Answer 3

Given that the tab on the AMS1117 (SOT223 housing) is the output, it will have the largest copper area to connect to and will be mechanically more stable.
I would connect the 7805 output pin directly to where the AMS1117 output was (middle pin, large solder pad.) I'd clip the other two wires short and use pieces of insulated wire to make the other two connections. That gives you a solid connection to the one solder pad best capable of supporting it, and flexible connections to the other two. I'd then use some hot melt glue or epoxy to give it some mechanical stability.

All of this assumes you are using the 7805 because you've got one at hand and need to get the Arduino going again without waiting on parts. As RYS says, the professionals would replace it with the correct part.

This also assumes nothing else died when the AMS1117 quit.

Also, be aware that the 7805 is not a low drop out part. If you have been using a 6Volt power supply then it won't work right with the 7805.

Answer 4

I am using a 12V DC supply. In any case, all answers given have made me reconsider and i am getting a replacement AMS1117-5v.

Given that you are using a 12V DC supply, and want 5V, you can leave broken AMS1117 and get a car usb charger. 12V in, regulated 5V out, better efficiency, less heat, neater package, and you can use the Arduino usb connector.