Mystery IC, need help identifying - Page 1
Forum section: electronics / repair

author: tyguy2
author_rank: Unknown
timestamp: October 08, 2015, 02:17:27 am
content: So I recently purchased a cheap Chinese Arduino Mega (it was only $9, so I wasn't expecting much), and with 3 weeks of troubleshooting my project, I accidentally shorted out what I presumed was a regulator and released the magic smoke. Does anyone know what type of regulator this is?

author: singapol
author_rank: Frequent Contributor
timestamp: October 08, 2015, 02:53:42 am
content: I don't know about this chinese clone but I think the regulator should be same or equivalent.On the official arduino mega 2560 R3 schematic it is listed asNCP1117ST50T3G.Check the datasheetfor the voltage output. It could be 3V or 3.3V.

author: tyguy2
author_rank: Unknown
timestamp: October 08, 2015, 02:55:12 am
content: Thanks, I'll give that a try tomorrow.

author: wraper
author_rank: Unknown
timestamp: October 08, 2015, 09:01:51 am
content: Quote from: singapol on October 08, 2015, 02:53:42 amNCP1117ST50T3G is 5V

author: tyguy2
author_rank: Unknown
timestamp: October 08, 2015, 01:14:31 pm
content: The voltage on the input pin is 5v, so I'm assuming it's a 3.3v regulator.

author: wraper
author_rank: Unknown
timestamp: October 08, 2015, 03:33:33 pm
content: Quote from: tyguy2 on October 08, 2015, 01:14:31 pmThen it is not NCP1117ST50T3GEDIT: I think it's 5V LDO because it should be for power input jack, but you get the pinout wrong.

author: Deathwish
author_rank: Unknown
timestamp: October 08, 2015, 07:41:09 pm
content: copies seem yo use a 800mA LDOhttp://www.elecfreaks.com/wiki/index.php?title=Freaduino_Mega2560

author: tyguy2
author_rank: Unknown
timestamp: October 09, 2015, 12:55:55 am
content: So I could still use the board if I didn't install the LDO (or just an LM805)? I'm using this mega with a RAMPS 1.4, so I'm not even sure if that part is needed, considering the board is powered via a 12 - 24 volt power supply.

author: singapol
author_rank: Frequent Contributor
timestamp: October 09, 2015, 02:48:27 am
content: Quote from: tyguy2 on October 09, 2015, 12:55:55 amPlease do yourself a favour and learn to help yourself. Do not blindly take advice but verify it for yourself.The regulator NCP1117ST50T3G is a fixed 5V output although usb has 5V supply , using 5V LDO ( low dropout regulator) will work even when input is down to 3.5V.It would filter out noisy 5V usb input. Auduino mega2560 mcu need 5V supply to run so it's aMUST. You need to replace with a good unit ( they come in 2 types of pakages so check again). 12 - 24V power supply is for the stepper motors only. BTW LM78XX will not work because it will need a 3V headroom to give 5V output so input is at least 8V and above. You could bypass the regulator and use usb only but I can't gaurantee performance or stability of arduino.http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF

author: promacjoe
author_rank: Regular Contributor
timestamp: October 09, 2015, 03:42:36 am
content: If you cannot find the proper regulator or just don't want to bother, remove the regulator and apply a regulated 5V directly to the 5V power pin.Note: On the Official Arduino schematic, the 3V3 has 5 pins. the 5V regulator has 4 pins/Solder connection points.Also note, never use an unregulated power supply on a Arduino. And never apply more than 12V to the power input port. Even though the specs say it can handle a higher voltage, It is not a good practice to run any regulator at it's upper limits. The regulator can heat up, and caused damage to your board.

author: singapol
author_rank: Frequent Contributor
timestamp: October 09, 2015, 04:56:01 am
content: Quote from: blueskull on October 09, 2015, 03:05:38 amIn a way you can say it is modern 78xxbut they are not interchangeble, usb 5V into 78xx will not work/regulate.78xx series start at 5V output so 5V into 5V 78xx is too low as it needs extra 3V so minimum input is 8V. LDO primary application are for battery powered devices. That's why it will work when 5V usb is used as 1117 will continue to regulate even when input is down to 3.5V ( for 5V 1117 ). Very suitable for battery/handheld devices.

author: tyguy2
author_rank: Unknown
timestamp: October 09, 2015, 01:50:00 pm
content: Well, I tried out a few options, and I think I'm just going to apply 5v. I'm using a 12v supply on the board, and when I put an LM117 on the correct pins, the board works perfectly. Since it works for what I need it to do, so I'm not too worried. Thanks for the help!

author: JoeB83
author_rank: Regular Contributor
timestamp: October 11, 2015, 05:03:24 am
content: Quote from: tyguy2 on October 09, 2015, 01:50:00 pmLM117 or LM1117? Both are voltage regulators, but the 117 is adjustable, and 1117s are fixed. Hopefully it's just a typo.LM117:http://www.ti.com/product/lm117LM1117:http://www.ti.com/product/lm1117-n