Author Topic: Creating voltage source from the output of an constant current LED driver  (Read 1029 times)

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Offline noddiTopic starter

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Hi,

I'm wondering if it is possible to create a constant (ish) voltage source of a constant current source (i.e. a LED driver)? I'm in a situation where the expected input from the supply I'm hooking up my system to was +48V, but recently learned that it was the output of a LDU4860 (Depended on some misleading documentation). There's also a challange with the changing system load, which changes between 100mA to 200mA peak when supplied directly from a +48V lab supply.

All input and help is strongly appreciated.
 

Offline dom0

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Re: Creating voltage source from the output of an constant current LED driver
« Reply #1 on: November 30, 2019, 03:35:12 pm »
48 V Zener or a shunt regulator (e.g. TL431 with extra pass element).
,
 

Offline magic

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Re: Creating voltage source from the output of an constant current LED driver
« Reply #2 on: November 30, 2019, 08:54:54 pm »
What's the output current from that thing and can you take it apart for modification?
I mean, zener will work, I wanted to jokingly suggest resistor, but power dissipation may become a bit crazy if the output current is high.
« Last Edit: November 30, 2019, 08:56:27 pm by magic »
 

Offline ocset

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Re: Creating voltage source from the output of an constant current LED driver
« Reply #3 on: November 30, 2019, 11:28:08 pm »
I mean really its not good to try and do it…but since you cant get inside the LDU4860, then maybe put a big cap on its output…then just  on/off switch it to keep the cap at approx. 48v…so a comparator looking at the cap voltage and feeding into the ldu4860 on/off pin…
 

Offline noddiTopic starter

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Re: Creating voltage source from the output of an constant current LED driver
« Reply #4 on: December 02, 2019, 09:03:51 am »
Thanks for all the replies!

What's the output current from that thing and can you take it apart for modification?

It can supply 1.75A in short circuit. Can't modify the LDU circuit at all, so I think trying to go the zener diode road. I'll give an update during the week on how it plays out.
 

Offline magic

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Re: Creating voltage source from the output of an constant current LED driver
« Reply #5 on: December 02, 2019, 12:09:25 pm »
It can supply 1.75A in short circuit.
How so? It's a constant current regulator, it should be outputting constant current, whether into load or into short.

If it really is 1.75A then a 48V shunt regulator will be dissipating 84W of heat under no load, are you sure you can handle it?

Actually, a series regulator like LM317 (or some high voltage variant thereof) would perhaps be better, depending on the maximum open circuit voltage the LED driver can output. Heck, even a switcher might pay for itself.
« Last Edit: December 02, 2019, 12:12:18 pm by magic »
 

Offline noddiTopic starter

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Re: Creating voltage source from the output of an constant current LED driver
« Reply #6 on: December 02, 2019, 02:42:32 pm »
How so? It's a constant current regulator, it should be outputting constant current, whether into load or into short.

If it really is 1.75A then a 48V shunt regulator will be dissipating 84W of heat under no load, are you sure you can handle it?

Sorry, I was a bit quick. I had a 48V isolated switching regulator in between, that gave the short circuit current. I was a bit quick on the measurement as well, and can't seem to reproduce it.

A special remark that might be an important point. on the output of the LDU is connected with a 110 Ohm power resistor in series. When short circuiting it I'm now measuring 430mA short circuit current and +48V over the resistor. The problem is that I can't touch those components, and have to find a way to live with it.

Actually, a series regulator like LM317 (or some high voltage variant thereof) would perhaps be better, depending on the maximum open circuit voltage the LED driver can output. Heck, even a switcher might pay for itself.

I'm open to everything. Not really in finding the cheapest solution.
« Last Edit: December 03, 2019, 03:56:38 pm by noddi »
 


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