Power Glitch Detection Circuit - Page 1
Forum section: electronics / projects

author: gyachts
author_rank: Newbie
timestamp: January 04, 2023, 05:49:23 pm
content: I'm working on a project where I need to detect a 0v pulse on a power supply line as a signal for loading.If the power supply line has no low voltage pulses then the circuit does nothing.If there is a pulse in the line going to 0v or near 0v, I want to detect the pulse so that I can latch the gate of a n-fet, using the simplest circuit possible.I was trying to use a detection circuit with a p-channel fet that would then switch the n-channel fet and latch it.When the pulse is present it is about 320us wide and repeats about every 8.7ms.The line voltage can be anywhere from 11v to 15v.I've attached a wave form example of the signal on the line.Any ideas or experience anyone can share would be appriciated.Greg

author: Terry Bites
author_rank: Super Contributor
timestamp: January 04, 2023, 06:17:08 pm
content: Use a 555 in bistable mode. Its negative edge triggered.

author: jwet
author_rank: Frequent Contributor
timestamp: January 05, 2023, 03:32:50 pm
content: At these speeds, I think I would put the uP in the loop. The problem with something that is just neg edge triggered only is that it would get tripped on each power down cycle. The unique thing about your trigger is the negative edge is followed by a positive edge in your max pulse width. You could detect the drop out with a comparator or logic gate, have this go to an interrupt and then have the uP watch for the rising edge in the right time window. Is this doable?- I don't know what you mean by "load" signal. If there's no uP, then I think some kind of more complex 555 type circuit or comparators with open collectors/open drains acting as monostables? LM393.

author: berke
author_rank: Frequent Contributor
timestamp: January 05, 2023, 05:41:09 pm
content: How about this. You didn't really specify what kind of supply you have for the monitoring side so I assumed 3.3V. Parts count 1x74HC132, 1 diode, two caps, 4 Rs.

author: Zero999
author_rank: Super Contributor
timestamp: January 05, 2023, 06:24:58 pm
content: What voltage threshold do you want it to trigger on?

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: January 05, 2023, 08:29:50 pm
content: Here's a purely analog solution using only passives and one comparator:https://falstad.com/circuit/circuitjs.html?ctz=CQAgjCCsB0AM8MYsBTAtAdnLaAmeuGGAzLABy4BsAnNVpLFFI5OmGAFACGI+Z41XCAAsYSgKH9IIRmCSNi0YuGgZcYfBmrC6sMJEFC5iDgCde5XpHGjxuazKiV4HAO4ixVm57CCZbi34+QK9-c2D7cTJGSMdjFwAlEMphEGJ8EBTHRmFZaUYC6EgzENjg4kghHIxYDgBnEIrJBUq4kAAXUwBXFA4k6LTW9MGqx1ymApkigNtQ2dwyflrzAdiB9Mn4jgBzEHWM9eJxApKxRizgrJiEPpCwDHFfIwfskQUlV5xigGMPO0XeOMFktwOh+GgwKp1EdIBQUrBKJRcFU4HoArggQCIg5akd+PMAcJVgCTu4zplUgMrgEqZSYjiOMQpCAAGIQTbSCEgAAyAEsAHYoAA6dQAbgB7AA27S4216TPAyjZjkUymERRAXIAKgALUwoOo6qUAEw4QASwitch on the bottom is for reset, and threshold can be adjusted by changing the voltage on the negative pin of the comparator.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: January 06, 2023, 07:52:22 am
content: Here's a simpler solution requiring only 2 transistors and 3 resistors:https://falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKAHMRs8AWEFBQpx6dIvKpBYAzPvj7cqeKinmcUfKLBTsQivgJ1K8eKFCl7Byql16XV6mJC0AnA32WvmaqmHgSX1t14AsBRjb18WAHdzOSV9FHcJaP4Ld10EsSihG3dMNQzTZIx83NlbJOzwUMrPQpqQjwaJACVGtV1CMRMVJHENBBYAZxjsNBj5PogAFycAVzptFJAJ8bBBcRYXNGNbbc5sdeQ4Fla97AOZYwC+lWZoPF6TGAGD43T3UcCnrKXRuIsVBIuOBBAAxCCTJBMEAANQA9gAbKYAQzYCyAA

author: gyachts
author_rank: Newbie
timestamp: January 06, 2023, 04:00:05 pm
content: Probably anything below 1-3 volts.Greg