# A regulator drops on high current

We have this really strange problem with a regulator on a circuit we have.

Usually it outputs a good 3.3V , from an input source of 5V. When we consume more current from the 5v source (not the REG output) , we get a voltage drop from 3.3V to 2.8V on the regulator output itself.

This happens only when we pass the 1.5A from the source itself.

The 5v source is capable of 4A , and it happens when we consume about 1.6A from the source. The source stay at 5V when the REG drops.

Please check the REG schematics here (c14, and c15 are in place) :

EDIT:

1. the regulator output is consuming less then 100mA.
2. I found out that the transformer source is indeed 4A output, but it says 0.68A maximum input - is that changes things ? how is that possible ? we replaced a few of them, non worked.
• Post the datasheet of the exact regulator in use!
– MAM
Commented Jan 20, 2017 at 8:50
• 1117 does not support that much current and is limiting the output for you to save itself from burning up. Feel it with your finger! Commented Jan 20, 2017 at 8:52
• It is unclear to me how much current you're drawing from this regulator's output. Commented Jan 20, 2017 at 8:54
• draw the complete schematic, including the ground connection, and where the 1.6A you are drawing is returning to ground. Look at your ground wiring carefully, try to estimate where it's good, and where it's a skinny or long wire, and show those details. More details about the power supply are required, so specify which one you are using (if commercial) or draw a schematic of it (if home-built). It's a good little puzzle, but you have more info than we do, and we don't have a enough to guess what the answer is. Commented Jan 20, 2017 at 9:23
• If you have an oscilloscope, use it on the input and output of the regulator. If you don't, try a multimeter on AC volts range. If it reads 0 with stable voltages, observe what happens when the anomaly occurs (if it doesn't read 0, forget it). Commented Jan 20, 2017 at 13:33