Output taking time to go to 0V - Page 1
Forum section: electronics / beginners

author: Freshman
author_rank: Regular Contributor
timestamp: June 24, 2024, 12:07:15 pm
content: I am using this AC-DC Module - LS01-K3B05SS (https://www.mornsun-power.com/html/pdf/LS01-K3B05SS.html)which converts 230V AC mains to 5V. When I turn off the 230V mains AC, the 5V takes around 10seconds to go to 0V.This 5V from the AC-DC module has a 220uF cap alone. Why does it take 10s for the 5V to go to 0V?

author: coromonadalix
author_rank: Super Contributor
timestamp: June 24, 2024, 12:49:55 pm
content: put a load resistor of 2k and see if it drop fasterif yes it would means the psu stay charged for a long time

author: Freshman
author_rank: Regular Contributor
timestamp: June 25, 2024, 02:36:24 pm
content: I have removed the capacitors at the output of the AC-DC module. Still the output takes a lot of time (10 seconds) to go to 0V.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 25, 2024, 02:43:47 pm
content: The power supply has capacitors inside it. Try with a load resistor as suggested.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 25, 2024, 03:58:38 pm
content: Judging by the initial question, I wonder if the OP realizes that the DC output is NOT isolated from the AC input!

author: Freshman
author_rank: Regular Contributor
timestamp: June 26, 2024, 02:54:59 am
content: If the AC input is not isolated with the DC output, then the output voltage should go to 0V immediately as I switch off the AC input right?Or what does it imply when you say AC input is not isolated with DC output in this context?

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 26, 2024, 03:33:17 am
content: What I mean, is that one wire of the high voltage mains (N) is directly connected to the low voltage output lead.(0v) It's a safety hazard if the user is not aware of it.Being isolated, or not, has nothing to do with your original problem of "When I turn off the 230V mains AC, the 5V takes around 10seconds to go to 0V."It's a shock hazard to anyone touching the 5V output wiring, or what it's powering, when it's plugged into 230 mains.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 26, 2024, 03:42:51 am
content: Any design that use non-isolated off-line PSU should accommodate for the inevitable end user plugging it backwards.Most mains standard don't even enforce L-N distinction, nor that they allow for your safety to rely on it being wired correctly.As for the original problem. Have you put the "bleeder" resistor as suggested, or test it connected to a load?Absent any load, most converter will simply turn off the switching transistors and the only bleeder path is whatever resistors used for feedback. Typically non-isolated supplies have much higher resistance because they don't need to operate tl431 and optocoupler.

author: IanB
author_rank: Super Contributor
timestamp: June 26, 2024, 05:55:36 am
content: Quote from: Freshman on June 25, 2024, 02:36:24 pmWhat do you mean, "you have removed the capacitors at the output of the module"?If the capacitors are part of the module, then removing them is a modification to the module, which is foolish and which may stop it from operating properly.If the capacitors are external to the module, then why were they there in the first place?

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 26, 2024, 06:02:09 am
content: Quote from: IanB on June 26, 2024, 05:55:36 amModules like this are usually shipped as functional barebone. You need to add your own bulk caps, output caps, X/Y caps, line filters, inrush mitigation and protections yourself if you want your product to meet advertised specs, safety and EMC regs.That being said you don't need to modify any components in the module itself. Not that it contain 220uF caps in the first place.

author: IanB
author_rank: Super Contributor
timestamp: June 26, 2024, 06:12:29 am
content: Quote from: ArdWar on June 26, 2024, 06:02:09 amThat makes sense.

author: soldar
author_rank: Super Contributor
timestamp: June 26, 2024, 10:34:57 am
content: Quote from: Freshman on June 26, 2024, 02:54:59 amNo. that is not how it works. I would advise caution because you are dealing with high voltage; voltage over your head.

author: rkabz
author_rank: Contributor
timestamp: June 26, 2024, 11:33:53 am
content: C1 and C2 will both cause the power supply to not go to 0V immediately. The discharge time is a function of both capacitors and the load on the power supply. You do not give details of the load current or resistance. In any case, removing C2 will allow the voltage to fall faster, but C1 still holds charge and will 'hold up' the power supply output for a period of time until it discharges. On the safety issue, if you are using this to power anything that has an external connection that you can touch, there is a danger of shock or electrocution, since one of the AC input terminals is commoned with the negative output terminal. If this common terminal is connected to the Line or Active side of the AC mains, it is very dangerous. An isolated power module will have no connection between any AC input terminal and output terminal. There will be a high resistance between any AC input and DC output to protect against electric shock.

author: soldar
author_rank: Super Contributor
timestamp: June 26, 2024, 12:24:58 pm
content: In any case, the specs cite a minimum load of 10% of max load so if that is not guaranteed by the circuit being fed then you should add a 250 ohm load resistor.

author: kevin.gibbs
author_rank: Regular Contributor
timestamp: February 05, 2025, 03:04:19 pm
content: While the load is not connected, the energy of the high-voltage capacitor C1 is used only to maintain the module's operation, and it discharges slowly.The disadvantage of the unit is that it is not isolated from the mains. Care must be taken when connecting AC(L) and AC(N).

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 07, 2025, 08:30:19 am
content: Quote from: Freshman on June 25, 2024, 02:36:24 pmAccording to datasheet the module has an input capacitor C1 1-22 uF which I guess is a main energy reservoir (but not output capacitor).

author: Zero999
author_rank: Super Contributor
timestamp: February 07, 2025, 12:27:28 pm
content: Don't modify it. Add a relay with a mains coil to the input and one of the contacts in series with the output.

author: BeBuLamar
author_rank: Super Contributor
timestamp: February 07, 2025, 01:10:40 pm
content: It's a power supply and most the output doesn't go off immediately when you disconnect the input power when there is no load at the output or very light load. That's normal. If you want to shut off the power quickly then put the switching device at the output.

author: CaptDon
author_rank: Super Contributor
timestamp: February 07, 2025, 01:25:35 pm
content: If you took out every capacitor it would drop quickly but it wouldn't work correctly either. Is that a real problem for you that it doesn't drop quickly? Do we know for sure one of the mains leads is actually carried through to the 5vdc side? I have laptop supplies that with no load on the output will hold their regulated voltage for 15 seconds or more. But that is not how they are used so it means nothing.