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Current limited LED and Difference between two types of capacitor

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Vraj

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Hi,

What is difference in current limited led and voltage limited led?
As far I know that the resistance of led is constant.
e.g. a led rated with 900mA and 12v.
I observed that the current at 12v is <900mA.
So why they only advise to use current limiter?
Voltage > rated voltage( in this case >12) can also cause damage.
Is current getting increased with increase in temperature for constant voltage?

I have to use smoothing capacitor rated with 1µF.

Aluminum Electrolytic Capacitors
Multilayer Ceramic Capacitors

both are same priced.

Which capacitor will be good?

Thanks
vraj
 

Hi,

As far I know that the resistance of led is constant.
Your "knowledge" is completely wrong.

r of a LED is very high ohmic with low voltages and very low ohmic at the rated operation area.

Therefore a minimal change in voltag causes a huge change in current.
Even a change in LED temperature nay cause the current to go above rated range.
--> you can´t handle it with pure voltage regulation.

Either use a lossy series resistor to relax the situation (but it makes no sense to use a lossy resistor combined with highly efficient LEDs)
Or use current regulation.

There are many, many discussions about LED control. Do a search within the forum or the internet.

***
capacitors:
Again: There are a lot of discussions and descriptions.
I´d prefer a ceramics capacitor - but I doubt they are same priced with same voltage and capacitance specifications compared to Al electrolytic capacitors.


Klaus
 
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    Vraj

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Nobody makes a 12V LED. the color of an LED sets its operating voltage. A red LED is about 2V and a white, blue or modern bright green LED is about 3.2V. Maybe you are talking about an LED that has a current-limiting resistor inside to be used with 12V or maybe it is actually a few 3.2V LEDs in series? Maybe it is an "LED Strip" that has a resistor in series with each LED?

If the type of LED or your circuit does not limit the current then when you feed it a voltage it will smoke and burn.
 
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    Vraj

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Hi,
Yes, it has 3 LED in series. It is COB LED
Thanks
 

As far I know that the resistance of led is constant.

Only if you knew the full form of LED you would have known better.

LEds are diodes.

Diodes conduct current only in one direction.

All diodes have a threshold voltage- below the voltage the resistance is high and above that (voltage) the resistance is low. The resistance in the reverse direction is very high.

The useful (working range) voltage of a diode is forward biased above the threshold voltage- this is the low resistance range of the diode.

You should also study the characteristic of the pn junction because that is essential to know why the diode is a current device rather than a voltage device.
 
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    Vraj

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Does it also have a ROB (resistor on board) that is in series with the LED chips?

Hi,
No internal led on board.
Thanks

- - - Updated - - -

Hi,

My point of view was different as there is 3 leds in series connted with very tiny may be gold wire in one chip.
So they are conductor and may be have ohmic resistance.
I think that tiny little wires are burning out and cause damage.
I was so deep in that and forgot that led is diode ;)

So, what you think in this case?

Thanks
 

What color light does your 12V/900mA COB LED (with 3 LEDs in series) produce? The approximate voltage of a red LED is about 2V and is about 3.2V for white blue and modern bright green LED. Then the value for the current-limiting resistor can be calculated.
If you do not limit the current then the tiny wires in the LEDs will burn out.
Please post the datasheet for the COB LED that you burnt out.
 
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    Vraj

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Hi,

I haven't Burnes out LED. I am planning to make led driver. My project is to make DJ light.
So there would be MOSFET in driving circuit.
I will amplify audio signal with opamp then will use comparator or uC to find peak and then will feed to the MOSFET.
MOSFET is rated with high current a snapshot voltage. I can use 12 v but worried about peak current which can cause damage to the led.
If I use current limiting resistor, than may be I loose brightness for very less turn on time.
This is home made project. Haven't choose led yet. But high power, easily available is having gold wires.
I will use white colour.
Without oscilloscope it is hard to work with.
Should I buy Chinese cheep one for start? DSO138 Oscilloscope (Full assembled)
**broken link removed**
(from AliExpress Android) because something is better than nothing ;)

Thanks
 

You have three freq bands: low, med and high. You also have three levels of intensity. One will be used to select the color and the other used to select the intensity. If you are using white LEDs then it does not matter: you select the intensity only.

peak current for a short time (consider the power) will not damage the LED.
 
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You have three freq bands: low, med and high. You also have three levels of intensity. One will be used to select the color and the other used to select the intensity. If you are using white LEDs then it does not matter: you select the intensity only.

peak current for a short time (consider the power) will not damage the LED.

Hi,

Hmm what about three level of intensity? Is it includes negative value?
Thanks

- - - Updated - - -

Hi,

Should I care about negative peak? How negative music sounds like? Do sound of drum has negative to positive or vice versa? Or neutral to positive or neutral to negative?
If it has 0(neutral) to negative then I should care about negative value.

How this sharpy light beam works?
The visible light beam! Do it having special frequency ? Do colour temperature effect? Or they are visible due to high intensity and low conducting cross section area?

Thanks
 

Hmm what about three level of intensity? Is it includes negative value?

Intensity is proportional to the square of the amplitude in a cycle; intensity therefore cannot be negative.

If you consider the equation E(t)=E_0 sin(omega.t), we normally consider E_0 as positive but the instantaneous value of E(t) can be either positive or negative.

Negative intensity is not possible.
 
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    Vraj

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The infrared LED in a remote control is blasted by very high current pulses but they have short durations so that the average power does not burn out the LED. But our vision takes time to see a pulse of light. A duration less than 30ms appears to have been dimmed.

I do not think our hearing or our vision cares about the polarity of pulses since if a speaker produces the pulse from a drum it is a pressure wave with a less than normal pressure wave behind it, or a less than normal pressure wave followed by a positive pressure wave. Then it is OK to half-wave rectify the signal because the rectified pulse occurs at both polarities.
 
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    Vraj

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Hi,

Do you know any audio buffer IC ? Or I should make it with op amps? I need this because I am using already two speakers from single input by direct parallel connection. Sometimes I observe noise signals / insufficient power for my speakers as input signal is driving two speakers.
I will use that Audio signal for driving led. So it is necessary to use buffer IC.

Thanks
 

But our vision takes time to see a pulse of light...

If you mean the response time of the brain, perhaps this is true. What is the response time of the eye (retina pigments) is what is relevant here. Most common camera flashes have a duration of 1ms or less. We still see them clearly. We can also see laser pulses that are us in durations. Human eye is pretty sensitive, we can see a single photon (dark adapted; at the wavelength corresponding to the max sensitivity) without problem (me excluded). What is important is the power and in the case of the eye we must consider the relaxation time (about 10-20 ms for most humans) and the camera flash will appear to be about 20ms duration; in fact all flashes shorter than 20ms will be stretches to this value.

The perception of intensity is more complex. When high intensity light falls on your eye, the pigments get bleached (headlight from the car coming in the opposite direction) and it takes longer to recover (of the order of 1s; less for young ones). Otherwise, the perception of the intensity is pretty good (log intensity) over a period of about 10-20ms.

The brain integrates mechanically.
 

Vrag mentioned overloading his audio amplifier by directly paralleling speakers and now he wants to overload the amplifier more by adding LEDs to its output. I guess he does not know that the noise (overload distortion?) and reduced power are from overloading the amplifier which might destroy it. An amplifier has a maximum allowed output current.

There were many power amplifier ICs available but now most are obsolete. The LM1875 is still produced and has an output power of 20W at low distortion into 4 or 8 ohms when powered by a 50VDC supply. It limits its output current to 4A and shuts down if it becomes too hot.
 

Hi,

Sir kindly check word "input"
noise signals / insufficient power for my speakers as input signal is driving two speakers

Means I am using now two different amplifiers and 1 common input.

Thanks
 

1) You did not describe the noise. Is it distortion, hiss or hum?
2) Your newest reply says that your input signal is driving two amplifiers but before it was driving two speakers in parallel.

Now I guess that you are overloading your input signal with two amplifiers that have input resistance too low for it to drive.
Why? Most input signals (MP3 player or something) have a fairly low output impedance from an opamp and most audio amplifiers have a fairly high input impedance. Your input signal should be able to drive a third amplifier that drives the LEDs.
 

Hi,

1) Yes I feel some distortion, power is felt low when I connect another amplifier.
2) Yes I should use clear words. speaker is having two meaning. The speaker manufacturer who creating speakers was also confused. When I asked Price list, he confused between multimedia speaker or transducer.

Yes you are write but I have experiance for decrease in volume . I have both analog and digital amplifier. May be this happening due to different characteristics of both inputs.

Thanks
 

We need to know what the signal comes from. An MP3 player, computer or radio tuner? Do you know its output impedance or can you post its schematic?
We also need to know the input impedance of your amplifiers.

The output impedance of most signal sources is 100 ohms or less and the input impedance of most amplifiers is 20k ohms or more. Then 200 amplifiers connected to a signal source produce a small drop in level with no increase of distortion.
 

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