What is the different between voltage overshoot and current overshoot? - Page 1
Forum section: electronics / beginners

author: skillz21
author_rank: Frequent Contributor
timestamp: October 30, 2019, 02:51:24 am
content: I watched this video:https://youtu.be/yIx_VWWgKUI?t=1521(I have set a timestamp). When the guy tests the power supply overshoot when the output is switched on, he sets the voltage to 10v, connects a 4.7ohm resistor (should draw 2.1A with no limit) and sets a current limit of 1A. He determines that the constant current mode kicks in and that the PSU limits the voltage to keep the current at the 1A limit.What I did not understand was the test he did following this one. He tests current overshoot by making a simple current shunt and measuring the voltage drop across it. He determines that there is a pretty significant current overshoot when a load is connected and PSU output is switched on (same testing scenario as test 1).I don't understand how, in the first example, he measured the voltage, and found that it stops at a lower voltage so that the current does not go over the 1A limit he set. But in the second example, he... contradicts this...?Could someone please explain what he means by the second test?

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 30, 2019, 02:57:19 am
content: Without watching the video, my guess is he's testing to see if power supply's ability to switch from CC to CV mode. So if he sets his current limit to 2A and he hits it with a short circuit, how close to 2A does it switch to CV.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 30, 2019, 03:29:02 am
content: Quote from: JustMeHere on October 30, 2019, 02:57:19 amNo, he's testing if there is any overshoot when initially powering up the output.

author: xavier60
author_rank: Super Contributor
timestamp: October 30, 2019, 11:40:39 am
content: CC loops are typically slow acting. As well as the external load current, the charge current of the internal output capacitor is also sensed.When the output voltage rises across the higher resistance load, the significant capacitor's charge current gives the CC loop enough time to act, preventing externally observed overshoot.The smaller resistance load causes a faster load current rise and to reach the CC setting more quickly, not giving the CC loop time to act.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 30, 2019, 08:52:21 pm
content: So he difference between the two tests is that for test 1, he has a 4.7ohm resistor, which draws less current than the 1ohm resistor he uses for the second test?But why did he format it like that? He says in the first test "it didn't allow the output voltage to overshoot". So that means it stopped once the current limit was reached, but for the second test, simply because the load is higher, Constant Current mode kind of falls apart?

author: xavier60
author_rank: Super Contributor
timestamp: October 31, 2019, 10:58:29 am
content: The lower resistance draws more current for a given voltage.Notice that both tests show a characteristic where the output quickly rises to about 1V regardless of load.I found that one of my power supplies had the same characteristic.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 31, 2019, 11:31:27 am
content: Ah, ok. I was kind of confused as to why, while doing the first test and there was no voltage overshoot, he pointed out that the PSU did have current overshoot.