can a flyback transformer for USB charger isolate?

[bohaboha]

can i use a flyback transformer from an usb charger to isolate galvanically a small diy led tester? or it must be an isolated transformer

[eccerr0r]

what are you trying to do, what hardware are you assuming?
A usb charger should be isolated as it is...

[bohaboha]

I was thinking of a led tester from a led lamp circuit

[sam_sam_sam]

I would recommend that you use a medical grade switching power supply most of the time made for quality than your general grade customer devices are if you are going to use it continuously every day type of uses

For my iPhone and iPad I use a medical grade switch power supply 5 volts at 5 amps switching power supply

But this is going to depend upon what voltage you plan to use and if you are going to test strings of LEDs lights which you have not mentioned yet or are just testing individual LEDs then a 5 volt switching power supply would work with a LM317 in the current mode

[eccerr0r]

Funny, when I near flyback transformers I always think about the second anode transformers for CRTs first and their associated high voltages... because that's where the name came from in the first place.

Again LED lamp circuit isn't very clear, suspecting a high voltage current limited supply to power long strings of LEDs, which seems a bit inadequate for wall wart 5V transformers...

[redwire]

The term came from CRT's, AFAIK. When the B-field in the transformer quickly collapses, it made the HV spike and the beam quickly "flies back" (blanked) back to the left edge.

[bohaboha]

Hi sam sam sam, eccerr0r and redwire and thanks for your answers it is intended for general use also to test black light without disassembling in terms of flyback transformer I thought if it is possible to use one from a usb charger or similar here I am waiting on your proposal to achieve the galvanic isolation and not use a charger as eccerr0r has perceived

[eccerr0r]

What "LED tester" are you using?
The general solution is to just get an isolation transformer. If you can't get one, you could get two identical voltage line frequency transformers and connect them back to back, and you get isolation that way. Of course there are limits to what you can do with this but for very low power it should be acceptable.
The optimal solution is to design the LED tester such that the isolation is built-in...

[bohaboha]

it is a diy tester from a led lamp circuit that needs to be isolated for safety but adding two identical voltage line frequency transformers will be clumsy if they are not small. can you use a small flyback transformer that you can find in a cell charger? or you may be able to refer to two small transformers that can be used.thank you

[redwire]

What voltage do you need for the LED string you are testing?
In Sweden they have many isolation transformers but developing countries they are too expensive.

For high voltage strings like in TV's you can use a 5V charger SMPS transformer connected backwards. They have isolation of course.

[bohaboha]

I have several 5v chargers I will disassemble some take pictures then you help me to choose the right one

[eccerr0r]

clumsy > electrocuted...

hmm suppose it is possible though a lot of hack work is needed...hmm...not as simple as back to back line frequency transformers...

[bohaboha]

so you think it's easier with back to back line frequency transformers? what size transformer should be able to have in this case

[eccerr0r]

not sure where people got the idea to use the transformer in switching psus? Doing it with line frequency isolation transformers or back to back identical transformers is much easier.

I'd like to see this switch mode transformer idea, it's possible but tricky to pull off...

[sam_sam_sam]

This post is getting interesting to follow more closely

[bohaboha]

I have seen several on youtoube but one was very interesting: DIY Backlight / LED Tester from LED tube .Watch it and say what you thought

[bohaboha]

https://www.youtube.com/watch?v=rhcaMuePo_o

[sam_sam_sam]

Originally Posted by bohaboha

https://www.youtube.com/watch?v=rhcaMuePo_o

Nice idea but I would want to be able to to select different current modes I will build one my self but have voltage and a current module so I do not have to have a meter hookup externally hooked up

Thank for sharing your idea I have a backlight tester but I do not like it limitations that they used

I would suggest that you use caution using this testing device and put it on the outside of the device what it is used for

[eccerr0r]

oh gawd 30 minutes of attention stealing, after breaking an apparently good LED lamp, stealing its driver circuit...

Then draws a schematic of a capacitor dropper circuit and then has some transformers which are uncommitted?

could someone summarize the rest of it in english?

(In other news from the recovery shop I got a 12-24v to 5v dc-dc converter. It was *DEAD*. So I had to open it, unfortunately it was potted in silicone. Yay silicone. Found that the output shunt appears to have fried and shorted out. Replaced it and looks like it's happy again. But this is totally unrelated to this thread, or is it?)

[sam_sam_sam]

Originally Posted by eccerr0r

(In other news from the recovery shop I got a 12-24v to 5v dc-dc converter. It was *DEAD*. So I had to open it, unfortunately it was potted in silicone. Yay silicone. Found that the output shunt appears to have fried and shorted out. Replaced it and looks like it's happy again. But this is totally unrelated to this thread, or is it?)

Yes it is but thanks for the update on your project