Fast and simple making of dual power supply with 2 led drivers

Thread Starter

mortenlund

Joined Mar 20, 2020
17
Hi Experts

I have salvaged 2 fine led drivers from some industry projector, really nice quality. They 70W - 33V Input: 85 - 265 VAC 50 - 60 Hz
Output: DC 30V - 36V 2.1A Waterproof! Ta:Max +50 Tc:Max +75 All inclosed in a thick aluminum casing.

I would like to simple and fast create a dual supply for testing some op amps in the range of maybe + / - 5V to 15V
I suppose each will drive the output to 36V because of constant current mode and the testing will be in the mA range. Quite overkill for this purpose, but they are at hand.
Cheapest, easiest way to set up - with some ripple accepted, manual voltage adjust, etc - is this meaningful and any suggestions is very welcome.
 

Thread Starter

mortenlund

Joined Mar 20, 2020
17
A constant current supply will not work for what you are trying to do. A simple bipolar supply is two 9V batteries.
(Need + - 15V)

Is it because the constant current supply cannot handle long term being driven to max? Heat or other reason?

I suppose it has a max voltage and will end there trying to output 2.1A, which will be limited by some large transistor outside of it.
At second thought I see the enormous heat development. Just dont want them to go to waste.
 

BobTPH

Joined Jun 5, 2013
8,661
Need + - 15V)
Then use four 9V batteries. How were planning to adjust the voltage between 5 and 15V?
I suppose it has a max voltage and will end there trying to output 2.1A, which will be limited by some large transistor outside of it.
You are only guessing. Operating something outside what is specified to do is always a bad idea, even when it looks like it works.
 

Thread Starter

mortenlund

Joined Mar 20, 2020
17
Then use four 9V batteries. How were planning to adjust the voltage between 5 and 15V?
I thought of something easier than like 2 x LM317 - and 2 x 2N3055 on a big heatzink? This is very common online circuit, but not really easy, but maybe it is the only way? And the battery solution is very fine, but does not use my 2 fine led drivers. Eager to put them to use.
 

BobTPH

Joined Jun 5, 2013
8,661
And the battery solution is very fine, but does not use my 2 fine led drivers. Eager to put them to use.
The way to put it to use is to get some LEDs to drive.

What is you ultimate purpose for the dual power supply? You said “testing some op amps in the range of maybe + / - 5V to 15V”.

Does that mean testing parts before using them in production, or trying out different circuits for learning purposes, or something else?
 

KeithWalker

Joined Jul 10, 2017
3,029
I thought of something easier than like 2 x LM317 - and 2 x 2N3055 on a big heatzink? This is very common online circuit, but not really easy, but maybe it is the only way? And the battery solution is very fine, but does not use my 2 fine led drivers. Eager to put them to use.
I see no reason why LM317s would not work as a good voltage regulated supply as long as the input voltage minus the output voltage never exceeds 40V. The LED drivers will just be a DC voltage supply with 2.1A maximum current limit. Just make sure that the ripple on the supply is filtered.
 

BobTPH

Joined Jun 5, 2013
8,661
I see no reason why LM317s would not work as a good voltage regulated supply as long as the input voltage minus the output voltage never exceeds 40V. The LED drivers will just be a DC voltage supply with 2.1A maximum current limit. Just make sure that the ripple on the supply is filtered.
How do you know they would not shut down when sensing too little load?
 

Thread Starter

mortenlund

Joined Mar 20, 2020
17
The way to put it to use is to get some LEDs to drive.

What is you ultimate purpose for the dual power supply? You said “testing some op amps in the range of maybe + / - 5V to 15V”.

Does that mean testing parts before using them in production, or trying out different circuits for learning purposes, or something else?
You are facing a newb. I am just learning op amps and savaged these 2 drivers which is so heavy and nice I thought they should be put into use. The op amp part is right now being done with a virtual ground made up with 2 resistors, so it kind of works. The fun with the led drivers was what I was really after.
 

Thread Starter

mortenlund

Joined Mar 20, 2020
17
I see no reason why LM317s would not work as a good voltage regulated supply as long as the input voltage minus the output voltage never exceeds 40V. The LED drivers will just be a DC voltage supply with 2.1A maximum current limit. Just make sure that the ripple on the supply is filtered.
Where does the 40V come from?

If they do not shot down, and do not get too hot, they could work perfect I hear. Thanks for input.
I have many concerns, one is oscillation between them, another is if they heat up trying to output 2.1A which will not be the case 99.9 % of the time and of course ripple - output might be ugly on a scope.
Would it be possible in some clever way to utilize the constant current part to get more stable voltage on expense of efficiency - was also a thought? At this moment I have left the plan about being easy and fast.
 

Jon Chandler

Joined Jun 12, 2008
985
An unclear point being missed here – are these CONSTANT CURRENT drivers intended to drive LEDs? Can you take a picture of any rating label on them?

If they are CONSTANT CURRENT drivers, they will do their best to maintain 2.1 amps output current. When no load is being applied, the output voltage rises to the maximum in an attempt to make 2.1 amps flow. Place a load like an incandescent headlight bulb on them, and the output voltage will drop to a few volts to limit current flow to 2.1 amps.

If you're only drawing up to a few hundred mA, they can probably be treated as constant voltage 30 volt supplies. So the first question to answer is if the outputs are isolated from powerline inputs and ground. If they are, then you should be able to create a bipolar power supply. Connect the positive output of one supply to the negative of the other. Do you measure 30v across each supply and 60 volts across the combined supply?

If yes, the next step is to add variable regulators. I suspect this is where you made your mistake. An LM317 positive regulator will supply plenty of current for using opamps. But you need an LM337 negative regulator for the negative side. The common point between the power supplies is "ground".

SmartSelect_20231024_101916_Edge.jpg
 

Thread Starter

mortenlund

Joined Mar 20, 2020
17
An unclear point being missed here – are these CONSTANT CURRENT drivers intended to drive LEDs? Can you take a picture of any rating label on them?


Thanks for mentioning the negative side LM337.
This is puzzling me. Would it not be possible, lets say LM337 was in backorder, to create it with 2 LM317. They after all adjust their output relative to the ground. One is moving the upper limit (the positive) and the other will get its ground (negativ) pushed further down from the real ground - center point? Is it because it would need individual adjustment for each separately, making it hard to get them exactely equal?
1698170875643.png
 

BobTPH

Joined Jun 5, 2013
8,661
And who knows what the voltage is with a 10mA load. 36 is the max voltage it can output at 2.1A, the no load voltage is bound to be higher than that.

I would never recommend using a device outside its specifications.
 

Thread Starter

mortenlund

Joined Mar 20, 2020
17
And who knows what the voltage is with a 10mA load. 36 is the max voltage it can output at 2.1A, the no load voltage is bound to be higher than that.

I would never recommend using a device outside its specifications.
I tested both. They deliver around 38 V with a 300 ohm load, few mV less with 100 ohm. It is peak to peak 1,3 V with 40 MHz and very spiky. They do not get hot! They even have a shotdown function for short circuit - tested accidentially.
Positive test I think! Of course this is meant to be only used by me in lab setup under observation.
 
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