What happens when you run less voltage to led?

[PicklesRus]

Hello.

If I have an LED board rated for 46V but I run it at 44v is it bad for the LED or driver? Will the led try to pull 46v and stress the driver? Will it stress te LEDs?

Thanks!

 

[CobKits]

what does "rated for" 46V mean?

keds can only pull current and voltage along their curve. if you restrict either it will reduce the other according to the curve

running LEDs soft does not stress them in any way

 

[Abiqua]

three things can theoretically happen...

it will light
it wont light
it blinks

typically i get blinking or non lighting.....the blinking is a feature too for emergency lights being able to sustain that blink for long periods on low voltage /low amperage fyi ....

 

[CobKits]

the blinking is a feature too for emergency lights being able to sustain that blink for long periods on low voltage /low amperage fyi .

how does that work? is there a capacitor in the driver circuit or cob itself?

 

[PicklesRus]

what does "rated for" 46V mean?

keds can only pull current and voltage along their curve. if you restrict either it will reduce the other according to the curve

running LEDs soft does not stress them in any way

I meant to say, the typical vf of the led board is 46vf.

So heres my next question. Using my example 46vf led- If I connect it to a constant voltage driver that puts out 56v, what will that do? What about connecting the 46vf led to a 30v constant voltage driver? I am trying to understand constant voltage drivers and I find matching LEDs to them totally confusing.

 

[CobKits]

Using my example 46vf led- If I connect it to a constant voltage driver that puts out 56v, what will that do?

depends on the current

 

[PicklesRus]

depends on the current

If the current is at or below the maximum for that part of the curve it will work?

 

[CobKits]

it can only run on the curve. if you limit voltage, and have ample current capacity, it will still only draw that max voltage. if you limit current, and have ample voltage, it will still only draw that max current

too much voltage with extra current not limited = boom

 

[PicklesRus]

Thank you

 

[CannaBruh]

double check max ratings for Vf, if it wants 46 and you give it 56 it might be really bright or it might make smoke, the 30V might or might not be enough to forward bias the thing on

 

[VegasWinner]

how does that work? is there a capacitor in the driver circuit or cob itself?

Low voltage cutout. Below rated volts will not work but blink or not light at all.

 

[PicklesRus]

it can only run on the curve. if you limit voltage, and have ample current capacity, it will still only draw that max voltage. if you limit current, and have ample voltage, it will still only draw that max current

too much voltage with extra current not limited = boom

What I'm confused about is the statement that I've heard here more than once it with the constant voltage driver if one of your chips blows then all the extra Amps get sent to the remaining chips .

So if your driver say for example is a constant voltage 40v driver with 4A and you have 10 40v leds connected in parallel what happens if some chips are removed? The extra current goes unused or does it get pushed to the leds?

 

[nfhiggs]

What I'm confused about is the statement that I've heard here more than once it with the constant voltage driver if one of your chips blows then all the extra Amps get sent to the remaining chips .

So if your driver say for example is a constant voltage 40v driver with 4A and you have 10 40v leds connected in parallel what happens if some chips are removed? The extra current goes unused or does it get pushed to the leds?

That statement is utter nonsense. The current through any LED is ENTIRELY dependent on the voltage applied and the LED junction temperature. If the voltage is constant, the current though the LED device is constant as well, barring temp shifts. Anything in parallel with it is irrelevant, unless the voltage supply is in current limiting mode - which means you've overloaded it and are just asking for trouble.

The only time that scenario can occur is if you are using constant current drivers and have devices in parallel on it. If one blows out, the driver raises the voltage to maintain the current through the rest of the devices.

 

[xX_BHMC_Xx]

That statement is utter nonsense. The current through any LED is ENTIRELY dependent on the voltage applied and the LED junction temperature. If the voltage is constant, the current though the LED device is constant as well, barring temp shifts. Anything in parallel with it is irrelevant, unless the voltage supply is in current limiting mode - which means you've overloaded it and are just asking for trouble.

The only time that scenario can occur is if you are using constant current drivers and have devices in parallel on it. If one blows out, the driver raises the voltage to maintain the current through the rest of the devices.

That's not true at all. If you run 5 36v cobs in parallel on a CV driver that puts out 36v and 2.1a, you get 420ma per cob. If one of those cobs fails, that 2.1a is now running through 4 cobs, still at 36v, meaning your 4 cobs are now running at 525ma. This is basic math man.

 

[nfhiggs]

That's not true at all. If you run 5 36v cobs in parallel on a CV driver that puts out 36v and 2.1a, you get 420ma per cob. If one of those cobs fails, that 2.1a is now running through 4 cobs, still at 36v, meaning your 4 cobs are now running at 525ma. This is basic math man.

It may be basic math, but it ISNT basic semiconductor physics - or even ohms law. The current through a junction is determined by the voltage applied. Nothing else (temperature excepted). The action you describe ONLY occurs with a Constant Current power supply, because the CC supply adjusts its voltage UPWARD to maintain current flow..

I've been working with electronics professionally for thirty plus years. I know how this shit works.

 

[CobKits]

That's not true at all. If you run 5 36v cobs in parallel on a CV driver that puts out 36v and 2.1a, you get 420ma per cob. If one of those cobs fails, that 2.1a is now running through 4 cobs, still at 36v, meaning your 4 cobs are now running at 525ma. This is basic math man.

it is impossible for cobs to run at both 420 mA and 525 mA and still be 36V. it can only operate on the curve (thermal droop excluded)

 

[xX_BHMC_Xx]

it is impossible for cobs to run at both 420 mA and 525 mA and still be 36V. it can only operate on the curve (thermal droop excluded)

For sure, I just threw out those numbers for an example.

 

[Abiqua]

For sure, I just threw out those numbers for an example.

so you threw out two wrong numbers deliberately?

 

[xX_BHMC_Xx]

It may be basic math, but it ISNT basic semiconductor physics - or even ohms law. The current through a junction is determined by the voltage applied. Nothing else (temperature excepted). The action you describe ONLY occurs with a Constant Current power supply, because the CC supply adjusts its voltage UPWARD to maintain current flow..

I've been working with electronics professionally for thirty plus years. I know how this shit works.

Thinking about it more, you're totally right. Apologies man, I was a few beers deep last night.

 

[nevergoodenuf]

Most of the CV drivers we use are also CC until it hits their max voltage (36v, 42v, etc). So as long as your COB draw less voltage, your driver is running on CC mode. A true CV driver wouldn't work that well for the way we build.