Oops! I made a 10:1 boost converter out of an AWG. How do I lower the voltage? - Page 1
Forum section: electronics / beginners

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: January 14, 2025, 06:14:21 am
content: [Solved!]Hello,Before you ask, I have no idea. The book series I read on electricity basically said that when dealing with low voltages and low currents (and no inductors, just plain wires), inductive effects would be negligible.Normally, I'm pretty careful about my circuit design. I calculate power dissipation and amperage to select components with sufficient capacity to handle the aforementioned. But inductance I've not had to calculate. I just never did anything that required it yet. I'm at a bit of a loss as to why things are going awry and how to perform the calculation to ensure it doesn't happen again.What happened was this:I ordered some LMV339IDR (comparators) from an unofficial source. I created a test setup using a buck converter to 2.7v, a bread board, a pair of 220 ohm resistors (for pulling up the comparator's outputs), and four LEDs. It seemed to be a genuine part but for one thing, the green LED wouldn't turn off. It was attached to channel 2.So, I probed the board with my oscilloscope using my AWG to feed in pulses to the various comparators in+ inputs (the AWGs negative input was not connected. I relied on the ground of the oscilloscope probe). On the right hand side of the board, everything looked good (well, not perfect wave forms, but I'm assuming that's because the LEDs were affecting the waveforms).On the left hand side, comparators 1 and 2, when stimulated with the AWG, were going crazy. I disconnected the LEDS and stuck some resistors I had laying around into the bread board without effect.I'm getting 27 volts from 2.7v!!!Now normally you'd need an inductor to do this, so what's inducing? I haven't the faintest. I've used my AWG in similar scenarios before, including with comparators. This has never happened.As I said above, I'm feeding 2.7v into the comparator and the AWG is set to +2.5v to 0v using a square wave. Frequency doesn't matter.Other things that don't matter include, turning off the 2.7v supply. The bypass capacitor. The resistance of the resistors. Whether the resistors are connected to the near or far side of the bread board. The placement of the oscilloscope's ground lead. Whether the AWG is grounded to the board directly (using a resistor so as not to short anything).What does work, quite well, is turning off the AWG. Obviously, it's the culprit, but how? It's coax->coupler->DMM adapter->wire->bread board->LM339IDR.I'm attaching pictures for your viewing pleasure. The oscilloscope is set for high-res acquisition and using color gradients. I should have taken internal screen shots, but I thought I'd record everything in case I wanted to know what I had done before. Before you ask, I don't have the internet BW to upload to YT or where ever. Sorry.The bread board, distance view and close up. The resistors too.The oscilloscope, AWG at 10khz with stats, without stats.The oscilloscope, AWG at 10hz with stats. (HZ NOT KHZ as above.)The oscilloscope, AWG 10khz stopped and then stopped and zoomed in.The oscilloscope, AWG on, power to the buck converter->LM339IDR turned off.How do I redo this circuit to test the LM339IDR-s without creating a boost convertor in the process?How do I avoid doing something like this in the future with another circuit?Thanks!PS: Here's a datasheet for the LM339IDR.https://www.ti.com/lit/gpn/lmv331EDIT: Fixed some grammar mistakes.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: January 14, 2025, 06:22:55 am
content: For some reason, two of my pictures were missing. Here they are.

author: ealex
author_rank: Frequent Contributor
timestamp: January 14, 2025, 06:35:43 am
content: hellois your probe set to 10x or 1x ?and also, is the scope set to the proper probe multiplier ?

author: CaptDon
author_rank: Super Contributor
timestamp: January 14, 2025, 02:03:46 pm
content: Schematic would be handy.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: January 14, 2025, 05:22:54 pm
content: You know, I always wondered why people on YT would print out the schematics. Now I know. It's far too easy to think that both sides of a chip are electrically symmetrical.Also, you were right about the probe being said to 1x. Normally, that's hard to do with a rigol probe, but I must have managed it somehow when doing my setup.Thanks guys! This might be close to a solution. I just have to rewire and retest.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: January 14, 2025, 08:16:05 pm
content: Wiring up the comparator properly and setting my probe to 10x worked!Thanks guys!BTW: Breadboards are rather fiddly things. Part of my problem was bad contact. I'm guessing that's why one LED wouldn't turn off.