Voltage drop out newbe question - Page 1
Forum section: electronics / beginners

author: DanielR
author_rank: Contributor
timestamp: May 17, 2014, 04:00:24 am
content: HiThis is a really basic question I suspect. I have search for the answer and not found an answer, perhaps I am asking the wrong question or terminology.I have two 5V devices on a power rail, one (LED strip) draw much more current and the other (embedded controller).When the LED strip turns on the current draw is much higher and voltage drops significantly and or course the digital controller stops working as the voltage drops well below the 5V.So how do I combat this? I can up the voltage on the power supply, but can't go too far as under no load it will have too high voltage. Both devices are absolutely 6v max. One idea I had was local regulate on both devices with common ground and just have higher PS voltage?Thanks for any suggestion.RegardsDanielGrounds of both devices need to be tied together. I am planing on running on battery of some type, but current are powering from a bench supply.

author: Joule Thief
author_rank: Regular Contributor
timestamp: May 17, 2014, 04:30:20 am
content: Daniel,what are the voltage and current requirements of the "LED strip"?The fact the output voltage of your power source is dropping significantly indicates it either has very poor voltage regulation properties or the load you are attaching - the LED strip - requires far more current than the supply can deliver.

author: RoMaNo
author_rank: Newbie
timestamp: May 17, 2014, 04:37:03 am
content: Hi Daniel,The voltage drop is due to your power supply isn't capable of deliver enough current for both devices. That means you are pushing that PS beyond its designed operation point, so you need to get a bigger one.Additionally when you turn your leds on and off you may cause undesired voltage transients in your controller power pins which can reset it.I would consider using different power supplies for each part of the circuit or at least one voltage regulator dedicated to your controller. A LM7805 should make the work.I hope that helps. Have a nice day!!

author: DanielR
author_rank: Contributor
timestamp: May 17, 2014, 04:48:55 am
content: I am using a RIGOL DP832 I have it set to 5.5V. If I measure the voltage at the outputs of the PS it is what it is set to i.e. 5.5V. If I measure at the circuit when the LED strip is off the voltage is 5.5V or there abouts, when the LED draws current (up to 2 amps if all on but not normally that much when modulating them) it is well below the 5.5V. The PS seems not to go into current limiting mode at all.I am a complete novice however so I probably have some thing wrong.I have tried to put some large caps on the board, seems not to help.I plan to run this on batteries at some stage probably Li-POs so I will need local regulation in the end.

author: RoMaNo
author_rank: Newbie
timestamp: May 17, 2014, 05:15:06 am
content: mmm yeah, that PS is big enough...If it doesn't go into current limiting mode I can't think in nothing else but the wires or something with how they are connected.You also mentioned there is some modulation. A schematic or a photo of your circuit will help to understand it better.

author: Rigby
author_rank: Super Contributor
timestamp: May 17, 2014, 05:18:56 am
content: If you have the LEDs and the micro in series, that could produce what you're describing. Try wiring them in parallel instead.