Dimming led light

[Gregory]

I have a 200 led light 1w per led 36.5v 6 AMP
To power the light I am using a 37v DC 30 Amp battery pack .Li-ion Polymer
I have looked for circuit but every one indicate to me that the light will pulsate.This is using a pot to vary the voltage.
This is a printout from the Voltage regulating circuit.

The LM317T is rated to output (subject to correct heat sinking) up to 1.5 Amps. If your requirement is for a high current voltage regulator then this article will show you how the addition of a PNP darlington transistor to an LM317T based voltage regulator circuit will enable much higher currents to be regulated safely.
Used in this way the transistor acts as a pass transistor since it carries the majority of the current while leaving sufficient current flowing through the LM317T to ensure reliable voltage regulati
Can you help me out with a circuit that will meat my requirements.
Thank you Greg

 

[Diver300]

You can dim LEDs very effectively by just reducing the current. It does not have to pulsate.

The lamp will have several strings of LEDs. I guess that it will have strings of 10 LEDs, totalling about 32 V, and each string has a LM317T to limit the current. There will be 20 strings like that, each taking about 0.3 A.

If you reduce the current to the entire lamp, it is likely that some strings will dim before others, because the LED voltages will be different. Even if all the LEDs are rated at 3.2 V, some might be 3.1 V and some 3.3 V, so the total voltage of a string could easily be 31.5 V or 32.5 V. If you reduce the current, the voltage will reduce, and it will reduce for the higher voltage strings first.

That is why many circuits turn the power to such a lamp on an off very quickly. That gets over the problem of some turning on before others, but introduces the problem that flicker may be visible, depending on lots of factors, including who is looking at it. Some people are much more sensitive to flicker than others.

If you want to reduce the current in each string of LEDs, you would need to post the existing circuit diagram.

 

[BioniC187]

Can you get a larger battery, say 50V? As it stands, this isn't gonna work. What is the light used for exactly? possibly go for PWM to try to attempt to make the battery last longer aswell. How long does the loght stay on when it is working?

 

[Gregory]

The led light that I am going to use and 36 V 6.5 Amp Hour DC battery pack will be used for underwater photography for a period of one hour. The dimming of the led's is to prevent light reflecting back when water is murky.
The dimming is of the leds is also for different exposures when filiming.
This is the reason to eliminate the flickering.
Hope this will help you to help me.
Thank you
Greg

 

[ronsimpson]

Can you turn off 1/2 of the LEDs.
Can you turn off 3/4 of the LEDs.
etc....

 

[Gregory]

No The led light is all one.
If I connect the led to my AC power supply and vary the vo[tage the led will not flicker will just dim as I would like it.
there is more leds out than If I reduce the current but there is only 2 out when at this current level.

If I reduce the current down to 5mA the voltage is 24V and it will not flicker this is as low as I will have to go.
By reducing the current will this shorten the life of the led.
Thank you
Greg

 

[ronsimpson]

By reducing the current will this shorten the life of the led.

No. Increasing the current will reduce the life.

 

[Gregory]

Will it be better for the led to decrease the current from max to min.
Or will it be better to reduce the voltsge.
I know when reducing eather current or voltage one will reduce when changing eather one
Could you point me in the direction of a circuit to reduce the current to suit the above current and voltage

 

[MrAl]

Hi,

For this kind of application you are better off using a buck type converter circuit. A buck circuit is a true POWER converter and so you see an increase in efficiency which equates to an increase in battery life.

A pulsing circuit (PWM) will produce a pulsing light yes which may be a problem for some photography applications, but it will also use more power even when dimmed than a true converter circuit like a buck. A buck will also provide a smooth output so there will be no pulsing along with higher efficiency. That means a longer run time per charge as well as a longer lasting battery.

 

[Gregory]

Could you advise me of the type of Buck circuit would suit my application \Could you supply a circuit digram
thank so much for your help

 

[MrAl]

Hi again,


Try this first:
https://www.linear.com/products/step-down_(buck)_regulators

 

[WTP Pepper]

This is common way to increase the current output of a 3 pin reg. Replace the 78XX with the LM317 config.


View attachment 65205

100mA flowing through the resistor will start to turn on the power tran and bypass the regulator while maintaining regulation. Fiddling with the resistors on the LM317 will alter the output voltage and thus the brightness.

Use an MJE2955 transistor on a heat sink.

 

[Gregory]

With the Lm317 You would have to have a Pot to vary the voltage.
I would like to vary the current up and down. This will change the voltage.
Will this be ok
Could you have a look at the High current circuit on this sight and Tell me what you think
But how do you vairy the current
http://www.reuk.co.uk/High-Current-Voltage-Regulation.htm

 

[WTP Pepper]

You wanted to vary the brightness. Varying the voltage will vary the current (not in a linear way) and therefore will vary the brightness.
What's the problem?